Field of the Invention
[0001] The present invention generally relates to the field of hydrocarbon exploration,
and more particularly to a method of evaluating physico-chemical conditions and
events during diagenesis of sedimentary rocks in a geological area, whereby, the
5 hydrocarbon potential of the sedimentary rock can be assessed.
Background of the Invention
[0002] Typically, diagenesis is defined as any chemical, physical, or biological change
undergone by a sediment after its initial deposition, and during and after its
lithification, exclusive of surface alteration and metamorphism. The fundamental
10 driving mechanisms for diagenetic reactions are changes in one or more of ambient
pore-fluid chemistry, temperature, and pressure. It has been observed that the
sedimentary mineral assemblage reacts through water–rock interaction via pore fluids
towards equilibrium with the ambient geochemical environment, therefore without the
presence of aqueous pore fluids diagenesis effectively ceases. Further, as the burial
15 history of a sedimentary basin develops, and pore fluids evolve through time, the
diagenetic fabric and mineralogy changes in response. Thus, diagenesis is considered
as a dynamic suite of processes, and the study of diagenetic events associated with the
sedimentary rocks is considered one of the key studies in hydrocarbon exploration of
sedimentary rocks in any geological area. Therefore, it is essential to accurately
20 evaluate physico-chemical conditions and events during diagenesis of sedimentary
rocks for accurate assessment of hydrocarbon potential of the sedimentary rocks.
[0003] Existing methods for evaluating diagenetic events associated with a selected
sedimentary rock, such as sandstone are based on mineralogical studies of core
samples extracted from selected sedimentary rock, where the mineralogical studies are
25 further conducted using state of the art petrographic techniques, such as Scanning
Electron Microscopy(SEM) and X-Ray Diffraction(XRD). However, the existing
methods do not consider variation in elemental concentration of the selected
sedimentary rock for evaluating diagenetic events, thereby causing inaccuracies in the
reconstruction of the physico-chemical conditions that have prevailed during the
3
respective diagenetic events. Further, the non-consideration of elemental
concentration prevents precise prediction and quantification of the diagenetic events,
and correlation of predicted diagenetic events with porosity and permeability of
selected sedimentary rock which is essential for hydrocarbon exploration. In particular,
5 the existing methods can identify diagenetic events that have occurred in the past for
any selected sedimentary rock. However, the existing methods do not provide an
estimate about the percentage of occurrence of any identified event. For example, if
diagenetic events, such as cementation or dissolution have been identified to have
occurred, the existing methods does not provide an estimate that a certain percentage,
10 such as 45% of cementation had occurred and 65 % of dissolution had occurred. The
quantification of diagenetic events is directly proportional to determination of
porosity, which in turn is relevant for assessing hydrocarbon potential of sedimentary
rock. Furthermore, the existing methods are inefficient in quantifying the selected
sedimentary rock as the existing methods rely on analysis of core samples collected
15 from two to three point depths of the selected sedimentary rock, which is not enough
to quantify the entire sedimentary rock. Yet further, the existing methods do not
consider the geochemistry associated with the diagenetic events which aids in inferring
the nature of original fluid that are responsible for the diagenetic events and
reconstructing the physico-chemical conditions that have prevailed during the
20 respective diagenesis processes.
[0004] In light of the aforementioned drawbacks, there is a need for a method which
can enable evaluation of precise physico-chemical conditions and events during
diagenesis of sedimentary rocks, whereby the sedimentary rocks can be characterised
and hydrocarbon potential of said sedimentary rocks can be assessed. There is a need
25 for a method which considers elemental concentration of sedimentary rocks for
evaluation of physico-chemical conditions and events associated with diagenesis of
said sedimentary rocks. Further, there is a need for a method which is geochemical in
nature and can be readily used for any sedimentary rock in any geological area.
Furthermore, there is a need for a method which has wider applicability and is easy to
30 implement. Yet further, there is a need for a method which is economical.
4
Summary of the invention
[0005] In accordance with various embodiments of the present invention, a method of
evaluating physico-chemical conditions and events during diagenesis at a depth (also
referred to as a zone) of a sedimentary formation is provided. The method comprises
5 obtaining water-based leachate, strong acid-based leachate and acetic acid based
leachate by leaching a core sample from the depth of the sedimentary formation in
water, strong acid composition and acetic acid, respectively. The method further
comprises determining environmental conditions, anionic concentration, and elements
and concentration of the elements at the depth based on an analysis of the obtained
10 water-based leachate. Further, the method comprises individually determining
elements and concentration of the elements at the depth based on an analysis of the
obtained strong acid-based leachate and the acetic acid based leachate. Finally, the
method comprises evaluating events prevailing during diagenesis at the depth of the
sedimentary formation along with the percentage of occurrence of said events based
15 on the environmental conditions, the anionic concentration, and the elements and the
concentration of the elements corresponding to said depth determined individually
based on the analysis of the water-based leachates, the strong acid-based leachates and
the acetic acid based leachates.
Brief Description of the Drawings
20 [0006] The present invention is described by way of embodiments illustrated in the
accompanying drawings wherein:
[0007] Figure 1 is a flowchart illustrating a method of evaluating physico-chemical
conditions and events during diagenesis of sedimentary rock formations in accordance
with various embodiments of the present invention;
25 [0008] Figure 2 is a graph representing pH values determined for respective waterbased leachates obtained from core samples extracted from respective depths
throughout a selected depth range of sedimentary formation in accordance with various
embodiments of the present invention;
5
[0009] Figure 3 is a graph representing evaluation of calcite cementation as an event
prevailing during diagenesis at one or more depths of the sedimentary formation; and
[0010] Figure 4 is a graph representing chlorite cementation as an event prevailing
during diagenesis at one or more depths of the sedimentary formation.
5 Detailed Description of the Invention
[0011] The disclosure is provided in order to enable a person having ordinary skill in
the art to practice the invention. Exemplary embodiments herein are provided only for
illustrative purposes and various modifications will be readily apparent to persons
skilled in the art. The general principles defined herein may be applied to other
10 embodiments and applications without departing from the spirit and scope of the
invention. The terminology and phraseology used herein is for the purpose of
describing exemplary embodiments and should not be considered limiting. Thus, the
present invention is to be accorded the widest scope encompassing numerous
alternatives, modifications and equivalents consistent with the principles and features
15 disclosed herein. For purposes of clarity, details relating to technical material that is
known in the technical fields related to the invention have been briefly described or
omitted so as not to unnecessarily obscure the present invention. It is to be noted that,
as used in the specification by the term “substantially” it is meant that the recited
characteristic, parameter, or value need not be achieved exactly, but that deviations or
20 variations, including for example, tolerances, measurement error, measurement
accuracy limitations and other factors known to those skilled in the art, may occur in
amounts that do not preclude the effect the characteristic was intended to provide. The
term “and/or” as used in the specification refers to all possible combinations and subcombinations of the listed elements, including any one of the listed elements alone,
25 any sub-combination, or all of the elements, and without necessarily excluding
additional elements. The term “sedimentary rock formation” refers to the formation
around the borehole drilled/bored in a sedimentary rock. The terms “sedimentary rock
formation” and “sedimentary formation” have been used interchangeably. The term
“selected sedimentary rock” as used in the specification refers to a sedimentary rock
30 selected for evaluation (in accordance with the present invention) out of various
6
sedimentary rocks in a geological area or an oil well. The term “selected depth range”
as used in the specification refers to the depth of basement reservoir selected for
hydrocarbon exploration. The term “depth” or “point depth” as used in the
specification refers to a zone within the formation indicated by depth. The term
5 “elemental concentration” as used in the specification refers to the concentration of
various elements in studied core samples and/or the sedimentary formation
corresponding to the core samples. The term “mineral composition” as used in the
specification refers to different proportions of elements or a group of elements forming
the mineral. The term “physico-chemical conditions” as used in the specification refers
10 to physical and chemical changes and/or reactions. The phrase “concentration of
elements” and “elemental concentration” have been used interchangeably in the
specification.
[0012] The present invention provides a method of evaluating physico-chemical
conditions and events during diagenesis of sedimentary rocks. In particular, the present
15 invention provides a method for geochemically evaluating physico-chemical
conditions and events during diagenesis of sedimentary rocks, such as sandstones,
whereby the sedimentary rocks can be characterised and hydrocarbon potential of said
rocks can be assessed. In operation, the method of the present invention comprises
extracting core samples from one or more depths(zones) throughout a selected depth
20 range of a well drilled/bored in sedimentary rock. Further, the method comprises
leaching the extracted core samples in three different solvents, selected from water;
strong acid composition comprising Suprapure acid(HNO3), HClO4 and HF; and
acetic acid to obtain water based leachates, strong acid based leachates and acetic acid
based leachates, respectively. Yet further, the method comprises determining
25 environmental conditions, anionic concentration and elemental concentration at one or
more depths throughout the selected depth range of sedimentary formation based on
analysis of the water-based leachates corresponding to the one or more depths. Yet
further, the method comprises individually determining elements and their
concentration at one or more depths throughout the selected depth range of
30 sedimentary formation based on analysis of the strong acid-based leachates and acetic
acid based leachates corresponding to one or more depths. Yet further, the method
7
comprises evaluating events prevailing during diagenesis at one or more depths
throughout the selected depth range of sedimentary formation along with the
percentage of occurrence of said events based on environmental conditions, anionic
concentration, and elemental concentration corresponding to said one or more depths.
5 Yet further, the characteristics of formation at respective point depths throughout the
selected depth range of sedimentary formation are assessed based on the identified
diagenetic events in view of the environmental conditions, elemental concentration,
and anionic concentration.
[0013] The present invention would now be discussed in context of embodiments as
10 illustrated in the accompanying drawings.
[0014] Referring to Figure 1, a flowchart illustrating a method of evaluating physicochemical conditions and events during diagenesis of sedimentary rock formations is
shown in accordance with various embodiments of the present invention.
[0015] At step 102, core samples are extracted from selected depth range of a
15 sedimentary formation. In an embodiment of the present invention, multiple core
samples are extracted from selected depth range of a well bored/drilled within a
selected sedimentary rock. In an example, a well having a depth ranging from 1000-
4000m may be drilled or bored in a sedimentary rock. Further, a depth ranging from
3000-4000m of the drilled/bored well may be assumed to be the depth of sedimentary
20 formation selected for evaluating physico-chemical conditions and events during
diagenesis. In the example, the depth ranging from 3000-4000 is a selected depth range
of the selected sedimentary formation. In the example, one or more core samples are
extracted from one or more depths separated by a preselected sampling range
throughout the selected depth range of 3000-4000m. In an example, assuming that the
25 preselected sampling range is 5m, the core or cutting samples are extracted from one
or more depths, such as 3000- 3005, 3005-3010, 3010-3015 up to 3995-4000m within
the selected depth range of 3000-4000m. It is to be understood, that the depth range of
3000-4000m is for exemplary purposes only, and the depth may differ based on the
well and/or user selection. Further, the depth/zones may be scattered throughout the
30 selected depth range of sedimentary formation and/or may be selected randomly.
8
[0016] At step 104, water-based leachates, strong acid-based leachates and acetic acid
based leachates are obtained by leaching the extracted core samples in solvents
selected from water, strong acids and acetic acid, respectively. In an embodiment of
the present invention, obtaining water-based leachates, strong acid-based leachates and
5 acetic acid based leachates comprises drying and grinding each of the core samples
extracted from selected depths of sedimentary formation. Subsequently, each core
sample is divided into three parts A, B and C. In an embodiment of the present
invention, the three parts A, B and C of each core sample are similar in properties and
substantially equal in quantity. One of the three parts(i.e. part A) of each of the
10 extracted core samples are leached in water to obtain solutions formed from each of
the extracted core samples and water. In an embodiment of the present invention, the
ratio of weight of core samples to volume of water is 1:5. In operation, 1gram of each
of the extracted core samples is added to 5ml of water. Further, each solution formed
from each of the extracted core samples and water is allowed to settle for 24 hours.
15 Each solution (of each the extracted core samples and water) is filtered to obtain waterbased leachates of core samples extracted from selected depths of sedimentary
formation. In a preferred embodiment of the present invention, distilled water having
pH in the range of 6.0-7.5 is used for water leaching.
[0017] In an embodiment of the present invention, another one of the three parts (i.e.,
20 part B) of each of the extracted core samples are leached in a strong acid composition
to obtain strong acid-based leachates. In an embodiment of the present invention, the
strong acid composition comprises Suprapure acid viz., Nitric acid (HNO3), Perchloric
acid (HClO4) and Hydrogen Fluoride (HF). In a preferred embodiment of the present
invention, the strong acid composition comprises HNO3, HClO4 and HF in the ratio of
25 3:3:4, i.e., 3ml of HNO3, 3ml of HClO4 and 4ml of HF. In operation, 0.15g of each of
the extracted core samples is added to respective 10ml strong acid composition and
allowed to dry on a hot plate heated at 170 0
C to obtain respective dry end-products.
Thereafter, the entire individual dry end-product obtained from each of the extracted
core samples and respective strong acid composition is further dissolved in respective
30 2% HNO3 (i.e., 2 ml of HNO3 diluted with 100ml water). Further, the respective
aliquot of solution formed from each dry end-product dissolved in 2% HNO3 is filtered
9
to obtain respective strong acid-based leachates. In an embodiment of the present
invention, the aliquot is filtered using Whatman 42 filter paper.
[0018] In an embodiment of the present invention, yet another one of the three parts
(i.e. part C) of each of the extracted core samples are leached in acetic acid to obtain
5 acetic acid based leachates. In an embodiment of the present invention, 3ml of 0.3%
acetic acid solution is used for leaching 0.1gm of core sample. In operation, 100mg of
each of the extracted core samples is added to respective 3ml of 0.3% acetic acid
solution, and allowed to settle for 24 hours. It is to be understood that 0.3% of acetic
acid solution is 0.3ml of acetic acid in 100 ml of water. Thereafter, respective aliquot
10 of solution formed from each of the extracted core samples dissolved in acetic acid is
filtered, dried and dissolved in 2(N)HCl to obtain acetic acid based leachates. In an
embodiment of the present invention, the aliquot is filtered using Whatman 42 filter
paper. In an embodiment of the present invention, the acetic acid is freshly prepared
glacial acetic acid.
15 [0019] For example- each of the core samples extracted from the selected depth range
of 3000- 3005, 3005-3010, 3010-3015 up to 3995-4000m are divided into three parts
and individually leached in distilled water samples, strong acid composition and acetic
acid to obtain water-based leachates, strong acid-based leachates and acetic acid based
leachates, respectively.
20 [0020] At step 106, environmental conditions, anionic concentration, and elemental
concentration throughout the selected depth range of sedimentary formation are
determined based on analysis of the obtained water-based leachates. In particular,
environmental conditions, anionic concentration, elements and their respective
concentration at one or more depths throughout the selected depth range of
25 sedimentary formation are determined based on analysis of the obtained water-based
leachates. In an embodiment of the present invention, determining the environmental
conditions throughout the selected depth range of sedimentary formation comprises
estimating pH of each of the water-based leachates obtained from respective core
samples extracted from selected depths of sedimentary formation. In an embodiment
30 of the present invention, the pH of each of the water-based leachates is estimated using
10
pH meter. In accordance with various embodiments of the present invention, the
determined pH of respective water-based leachates is indicative of oxidizing or
reducing environment conditions around the depth of sedimentary formation
corresponding to the core samples used for obtaining the water-based leachates. For
5 e.g.: assuming pH of a water-based leachate obtained from core sample extracted from
a depth of 3605m is 6.48. The pH value of 6.48 of the water-based leachate indicates
the environment around the depth 3605m of the sedimentary formation. In particular,
the pH of 6.48 is indicative of acidic conditions which implies that the environment
around the depth 3605m of the sedimentary formation is oxic or oxidizing. In another
10 example, assuming that the pH of water-based leachate obtained from core sample
extracted from a depth of 3680 m is 9.0, then said pH is indicative of alkaline
conditions, which further implies that the environment around the depth 3680m of the
sedimentary formation is anoxic or reducing. A graph representing pH values
determined for respective water-based leachates obtained from core samples extracted
15 from respective depths throughout a selected depth range of sedimentary formation is
shown in figure 2. As shown in figure 2, the change in pH value and/or the
environmental conditions throughout the selected depth range is indicative of chemical
shift.
[0021] In an embodiment of the present invention, each of the said water-based
20 leachates are subjected to Ion Chromatography and analysed for determining anionic
concentration at each of the one or more depths within the selected depth range of
sedimentary formation. Yet further, each of the said water-based leachates are
subjected to Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES)
and analysed for determining elements and concentration of the elements at each of
25 the one or more depths throughout the selected depth range of sedimentary formation.
In an embodiment of the present invention, the water-based leachates may include one
or more of the following eight anions Fluoride, Chloride, Carbonates, Bicarbonates,
Phosphates, Sulphates, Iodide, and Bromide. In an embodiment of the present
invention, the water-based leachates may include one or more of the following 18
30 elements (Fe, Mg, Al, Na, K, Ca, Zn, Mn, V, Ti, Sr, Rb, U, Cu, Ni, Co, Cr and P). In
accordance with various embodiments of the present invention, the determined anionic
11
concentration, elements and elemental concentration of respective water-based
leachates is indicative of anionic concentration, elements and elemental concentration
at respective depths of sedimentary formation wherefrom corresponding core samples
were extracted for obtaining the water-based leachates.
5 [0022] For example: the analysis of water-based leachates for anionic concentration
may indicate the presence of one or more of the eight anions Fluoride, Chloride,
Carbonates, Bicarbonates, Phosphates Sulphates Iodide and Bromide. The presence of
one or more aforementioned anions and their concentration in a water-based leachate
is indicative of presence of one or more anions and their concentration in selected
10 depth of sedimentary formation wherefrom the core sample was extracted to obtain
said water-based leachate. Further, the presence of anions and their concentration at a
selected depth of sedimentary formation is indicative of chemical process that said
sedimentary formation has undergone. For instance, a high carbonate concentration
associated with one or more selected depths of the sedimentary formation implies
15 calcite cementation process at said depths. Similarly, a high sulphate concentration at
one or more depths is indicative of bacterial activity at said depths.
[0023] In another example, elements, such as Calcium and Magnesium may be
identified in certain concentration in water soluble form such as, hydroxides, sulphates,
Phosphates etc. based on the analysis of water-based leachates(obtained from core
20 samples extracted from depth 3710m of the sedimentary formation). The elements Ca
and Mg and their concentration in the water-based leachates is indicative of elemental
concentration at depth 3710m of sedimentary formation wherefrom corresponding
core sample was extracted for obtaining the water-based leachate.
[0024] At step 108, elements and their concentration throughout the selected depth
25 range of sedimentary formation is individually determined based on analysis of the
obtained strong acid-based leachates and acetic acid based leachates. In an
embodiment of the present invention, elements, and their concentrations at multiple
point depths within the selected depth range of sedimentary formation is determined
based on the analysis of the obtained strong acid-based leachates. In operation, each
30 of the strong acid-based leachates obtained by dissolving respective core samples
12
(obtained from respective point depths of the sedimentary formation) in the strong
acids are subjected to Inductively Coupled Plasma - Optical Emission Spectrometry
(ICP-OES) and analysed for determining elements and their concentration at each of
the one or more depths of sedimentary formation. In an embodiment of the present
5 invention, respective strong-acid based leachates are analysed for 18 elements
including iron(Fe), Magnesium(Mg), Aluminium(Al), sodium(Na), potassium(K),
calcium(Ca), Zinc(Zn), Manganese(Mn), Vanadium(V), Titanium(Ti), Strontium(Sr),
Rubidium(Rb), Uranium(U), Copper(Cu), Nickel(Ni), Cobalt(Co), Chromium(Cr),
Phosphorus(P), and 17 rare earth elements Cerium(Ce), Dysprosium(Dy), Erbium(Er),
10 Europium(Eu), Gallium(Ga), Holmium(Ho), Lanthanum(La), Lutetium(Lu),
Neodymium(Nd), Praseodymium(Pr), scandium (Sc), samarium(Sm), Terbium(Tb),
Thorium(Th), Thulium(Tm), Yttrium(Y), and Ytterbium(Yb). Accordingly, the
respective strong acid-based leachates may include one or more of the following 18
elements (Fe, Mg, Al, Na, K, Ca, Zn, Mn, V, Ti, Sr, Rb, U, Cu, Ni, Co, Cr and P)
15 and/or one or more of the following 17 rare earth elements (Ce, Dy, Er, Eu, Ga, Ho,
La, Lu, Nd, Pr, Sc, Sm Tb, Th, Tm, Y, Yb). In accordance with various embodiments
of the present invention, the determined elements and elemental concentration of
respective strong acid-based leachates is indicative of elements and elemental
concentration at respective depths of sedimentary formation wherefrom corresponding
20 core samples were extracted for obtaining the strong acid-based leachates.
[0025] For example: the analysis of strong acid-based leachates for elements and their
concentration may indicate the presence of one or more of the 35 elements at one or
more depths within the selected depth range of sedimentary formation. The presence
of one or more of the 35 elements and their concentration in strong acid-based
25 leachates is indicative of the presence of one or more of the 35 elements and their
concentration at respective depths of sedimentary formation wherefrom the core
samples were extracted to obtain said strong acid-based leachates. Assuming, that the
strong acid-based leachates (obtained from a core sample extracted from the depth of
3610m) indicated the presence of iron (Fe) at a concentration of 10%, then said
30 determined elemental concentration of iron, is the concentration at a depth of 3610m
of the sedimentary formation wherefrom the core sample was extracted.
13
[0026] In an embodiment of the present invention, elements and their concentrations
at each of the one or more point depths within the selected depth range of sedimentary
formation is determined based on the analysis of the obtained acetic acid based
leachates. In operation, each of the acetic acid based leachates obtained by dissolving
5 respective core samples (obtained from respective point depths of the sedimentary
formation) in acetic acid are subjected to Inductively Coupled Plasma - Optical
Emission Spectrometry (ICP-OES) and analysed for determining elements and their
concentration at each of the one or more depths of sedimentary formation. In an
embodiment of the present invention, each of the acetic acid based leachates are
10 analysed for 6 elements including iron(Fe), Magnesium(Mg), Aluminium(Al),
sodium(Na), potassium(K), and calcium(Ca). Accordingly, the respective acetic acid
based leachates may include one or more of the following 6 elements (Fe, Ca, Mg, Na,
K and Al). In accordance with various embodiments of the present invention, the
determined elemental concentration of respective acetic acid-based leachates is
15 indicative of elemental concentration at respective depths of sedimentary formation
wherefrom corresponding core samples were extracted for obtaining the strong acidbased leachates. For example: the analysis of acetic acid based leachates for elements
and their concentration may indicate the presence of one or more of the 6 elements
(Fe, Ca, Mg, Na, K and Al) at one or more depths within the selected depth range of
20 sedimentary formation. The presence of one or more of the aforementioned elements
and their concentration in acetic acid based leachates is indicative of the presence of
one or more elements and their concentration at respective depth of sedimentary
formation wherefrom the core sample was extracted to obtain said acetic acid based
leachate. Assuming, that the acetic acid based leachate (obtained from a core sample
25 extracted from the depth of 3650m) indicated the presence of calcium (Ca) at a
concentration of 20%, then said determined elemental concentration of Calcium, is the
concentration at depth 3650m of the sedimentary formation wherefrom the core
sample was extracted.
[0027] At step 110, events prevailing during diagenesis throughout the selected depth
30 range of sedimentary formation along with the percentage of occurrence of said events
are evaluated based on either of the determined environmental conditions, anionic
14
concentration, elemental concentration throughout the selected depth range of
sedimentary formation or any combination thereof. The events prevailing during
diagenesis are hereinafter referred to as diagenetic events. In an embodiment of the
present invention, one or more diagenetic events and their respective percentage of
5 occurrence at respective point depths throughout the selected depth range are evaluated
based on the environmental conditions and anionic concentrations determined using
water-based leachates, and elements and their concentrations determined individually
based on the water-based leachates, strong acid-based leachates and acetic acid based
leachates. In an embodiment of the present invention, the diagenetic events and their
10 percentage is evaluated using one or more data analysis techniques, whereby
environmental conditions determined using water-based leachate, anionic
concentrations determined using water-based leachates, and elements and their
concentrations determined individually based on the water-based leachates, strong
acid-based leachates and acetic acid based leachates are correlated. In an embodiment
15 of the present invention, the data analysis may be performed manually. In another
embodiment of the present invention, the data analysis may be performed via one or
more computing devices, such as a desktop, laptop, supercomputer, micro-computer
or any other device capable of processing data using specific data analytics rules and/or
machine learning. The data analytics rules are predefined based on predetermined
20 correlations between various elements and anions in view of environmental conditions
(such as oxidizing or reducing conditions).
[0028] In yet another embodiment of the present invention, the diagenetic events and
their percentage is evaluated using data analysis in conjunction with a predefined
correlation database. The predefined correlation database is used for correlating the
25 environmental conditions and anionic concentrations determined using water-based
leachates, and elements and their concentrations determined individually based on the
water-based leachates, strong acid-based leachates and acetic acid based leachates. In
an exemplary embodiment of the present invention, the correlation database comprises
information regarding elements, their chemical relationship with respect to each other
30 in varying conditions, chemical reactions between elements and anions in presence of
other elements and anions, probable chemical processes and paleo-weathering patterns
15
in view of various elements and relative variation of said elements with respect to other
elements, well logs associated with a well bored/drilled in the sedimentary rock being
explored (i.e. well logs associated with the sedimentary formation) etc.
[0029] In operation, evaluating the diagenetic events and their percentage of
5 occurrence comprises evaluating the minerology throughout the selected depth range
of the sedimentary formation. In an embodiment of the present invention, one or more
minerals at multiple depths throughout the selected depth range of sedimentary
formation are evaluated by correlating the elements and their associated concentration
determined via water-based leachates, strong acid-based leachates and acetic acid
10 based leachates in view of determined environmental conditions and anionic
concentration using data analysis and/or correlation database. In operation, one or
more probable mineral compositions (also referred to as mineralogy) at each of the
multiple depths throughout the selected depth range of sedimentary formation is
evaluated by correlating the elements determined via water-based leachates, strong
15 acid-based leachates and acetic acid based leachates at same depth in view of
determined environmental conditions and/or anionic concentration at the same depth
using data analysis and/or correlation database. It is to be understood that at some
depths no element may be determined/identified from the analysis of water-based
leachate and/or acetic acid based leachate obtained from said depths, however one or
20 more elements might be determined/identified based on the analysis of strong-acid
based leachate for the same depths. Similarly, at some depths no element may be
determined/identified from the analysis of water-based leachate obtained from said
depths, however one or more elements might be determined/identified based on the
analysis of strong-acid based leachate and/or acetic acid based leachate for the same
25 depths. Further, it is to be understood that at some depths same element with variation
in concentration may be determined based on individual analysis of water-based
leachates, strong-acid based leachate and acetic acid based leachates(obtained from
said depths). Yet further it is to be understood that at some depths different elements
may be determined based on individual analysis of water-based leachates, strong-acid
30 based leachate and acetic acid based leachates(obtained from said depths).
Accordingly, the elements determined via water-based leachates, strong acid-based
16
leachates and acetic acid based leachates at same depth are correlated in view of
determined environmental conditions and anionic concentration at the same depth.
Further, the evaluated one or more probable mineral compositions are correlated with
concentration of elements and anions forming said probable mineral compositions to
5 evaluate the one or more minerals at the respective depths. In an example, assuming,
Calcium and Magnesium are identified (in water soluble form such as, hydroxides,
sulphates, Phosphates etc.) at a depth of 3680m based on the analysis of water-based
leachates. Further assuming the presence of calcium (Ca), Magnesium, and Si is
determined at a depth of 3680m of the sedimentary formation based on an analysis of
10 strong-acid based leachate and acetic acid based leachate. Yet further, assuming that
carbonate is also determined at the same depth based on the analysis of water-based
leachates. Also, the presence of elements calcium (Ca) and Magnesium based on
water-based leachates and acetic acid based leachates confirms the presence of
carbonates of Ca and Mg at depth 3680m. Yet further, assuming that the pH at the
15 depth 3680 is alkaline indicating reducing environment. Based on the determined
elements, anions, and environmental conditions one or more probable mineral
compositions which may exist after physico-chemical reactions between calcium,
magnesium, Si, and carbonate are evaluated using data analysis. Yet further, the one
or more minerals and the concentration of minerals at depth 3680m is ascertained by
20 correlating the evaluated one or more probable mineral compositions with determined
concentration of the respective elements and anions (i.e., concentration of calcium,
magnesium, Si and Carbonate) at the depth of 3680m.
[0030] Yet further, the diagenetic events that have prevailed at respective depths
throughout the selected depth range of sedimentary formation are determined based on
25 the evaluated one or more minerals or determined concentration of elements or a
combination thereof at corresponding depths in view of the environmental conditions
(determined based on the pH) using data analysis. In an embodiment of the present
invention, the evaluated diagenetic events are associated with one or more of the
following categories: physical processes, chemical processes, and biochemical and
30 organic processes. Examples of physical processes may include sediment influx and
weathering. Examples of chemical processes may include, but are not limited to
17
cementation, dissolution, dolomitization, recrystallization etc. Examples of
biochemical and organic events may include, but are not limited to, generation and
depletion of sulphates, nitrites etc. due to bacterial activity caused by aerobic and/or
anaerobic bacteria. For example: the first step in diagenesis is formation of soil, which
5 is a step considered under the process of weathering. In order to understand the source
of soil, the provenance is understood based on elemental concentration at various
depths which is determined based on an analysis of strong acid-based
leachates(obtained from core samples of said depths). Yet further, the formation of
carbonates cements, Dolomitization is analysed based on acetic acid based leachates.
10 Formation of mineral quartz may be understood from analysis of strong-acid based
leachates and environmental conditions (determined based on the pH). In conclusion,
environmental conditions (determined based on the pH) are indicative of the
favourable conditions for different types of diagenetic events, and minerals and/or
elemental concentration are used for quantifying the diagenetic event, i.e. the
15 percentage of occurrence of a diagenetic event.
[0031] Yet further, the diagenetic events across the two or more continuous points
depths throughout the selected depth range are evaluated based on diagenetic events
at respective depths using extrapolation. For instance, assuming a depth ranging from
3000-4000 is a selected depth range of the selected sedimentary formation. In the
20 example, multiple core samples are extracted from the selected depth range of 3000-
4000m with a preselected sampling rate. Assuming that the preselected sampling rate
is 5m, the core or cutting samples are extracted from the multiple depths, such as 3000-
3005, 3005-3010, 3010-3015 up to 3995-4000m within the selected depth range of
3000-4000m. Assuming, that the diagenetic events at point depths 3000, 3005, 3010
25 up to 4000 have been evaluated, the diagenetic events for 5m range between each of
the point depth, such as 3000-3005 are evaluated using extrapolation. Assuming, that
the diagenetic events at 3000m and 3005 m are the same, then using extrapolation the
diagenetic events between 3000-3005m can be evaluated. In another example, the
diagenetic events between 3000-3005m can also be evaluated assuming that the
30 elements, elemental concentration, environmental conditions, anionic concentration
etc. are the same at the point depths 3000m and 3005m.
18
[0032] EXAMPLES OF EVALUATING SPECIFIC DIAGENETIC EVENTS IN
ACCORDANCE WITH THE METHOD OF PRESENT INVENTION
[0033] Example 1: Diagenetic Event- Calcite cementation
[0034] It has been observed based on studies performed on corroded quartz boundaries
5 using Scanning Electron Microscope (SEM) that in alkaline environment calcite
(CaCO₃) precipitates and quartz (SiO2) gets dissolved. Additional phenomenon which
is associated with formation of mineral dolomite (CaMg(CO3)2) is the decrease in
concentration of magnesium in water. In view of above observations (which may be
maintained in a correlation database), the diagenetic events at one or more point depths
10 throughout the selected range of sedimentary formation are evaluated using data
analysis on the determined environmental conditions, anion concentration, elements
and their concentration at respective point depths. Assuming, Calcium, Magnesium,
and Si are the elements determined at depth of 3830m, and carbonate is the anion at
depth 3830m. The foregoing combination of elements and anions, indicate the
15 probability of Calcite, dolomite and quartz. However, based on the concentration of
each of the elements and environmental conditions, the exact mineral may be
evaluated. Assuming, the environmental conditions at depth 3830m are alkaline
(reducing) and the concentration of calcium is increasing in relation to the
concentration of magnesium. Accordingly, the diagenetic event is calcite cementation.
20 In another, scenario a significant decrease in concentration of calcium in relation to
silica at depth 3830m would indicate quartz overgrowth. Referring to figure 3, a graph
representing evaluation of calcite cementation as an event prevailing during diagenesis
at one or more depths of sedimentary formation is shown in accordance with various
embodiments of the present invention. As shown in figure 3, the average silicon
25 concentration at depth 3834.90m(indicated by symbol -) decreases and the pH is
alkaline (>7) indicating Calcite precipitation.
[0035] Example 2: Diagenetic Event- Iron oxide cementation
[0036] It has been observed that Iron oxides, Sulfides and some carbonates, such as,
but not limited to siderite (FeCO3), ankerite (Ca (Mg, Fe2+, Mn) (CO3)2) and pyrite
19
(FeS2) are strongly controlled by Oxidation/Reduction Potential (Eh) and pH
conditions. Further, it has been observed that under oxidizing conditions, formation of
iron oxides take place, whereas under reducing conditions, pyrite (FeS2) or siderite are
formed, depending on the relative sulfide and carbonate concentrations. Furthermore,
5 it has been observed that reducing environmental conditions are indicative of late
diagenetic phase. Yet further, it has been observed that the formation of pyrite is
always an outcome of bacterial activity, whereas siderite formation is always an
outcome of chemical activity, and in terms of order of occurrence bacterial activity
occurs before chemical activity. Accordingly, even in late diagenetic phase pyrite will
10 be formed earlier compared to the formation of siderite. In view of above observations
(which may be maintained in a correlation database), the diagenetic events at one or
more points depths throughout the selected range of sedimentary formation are
evaluated using data analysis on the determined environmental conditions, anionic
concentration, elements and elemental concentration at respective point depths.
15 Assuming, Fe, Magnesium, and Sulphur are the elements determined at the depth of
3650m based on the analysis of leachates(obtained from core sample of 3650m), and
carbonate is the anion at depth 3650m. The above combination of elements and anions,
indicate the probability of iron oxides, siderite (FeCO3) and pyrite (FeS2). However,
based on the concentration of each of the elements and environmental conditions, the
20 exact mineral may be evaluated. Assuming, the environmental conditions as evaluated
for depth 3650m based on pH are acidic (oxidizing) then iron oxides are formed. The
acidic pore fluids increase the solubility of any iron bearing minerals present in the
sediment indicating that the diagenetic event is iron oxide cementation. Assuming, the
environmental conditions at depth 3650m are alkaline (reducing) and the concentration
25 of carbonate are relatively more than sulfide, indicating the formation of siderite
(FeCO3), further indicating chemical activity. Similarly, if the concentration of
sulfides are relatively more than carbonates, this indicates the formation of pyrite
(FeS2), and further indicates bacterial activity.
[0037] Example 3: Diagenetic Event- Feldspar Dissolution
20
[0038] Feldspar is a group of naturally occurring alumino-silicate minerals containing
varying amounts of potassium(K), sodium(Na), calcium(Ca), and/or lithium(Li). It is
known that the dissolution mechanism of feldspar involves following three successive
steps: (1) Instantaneous exchange of alkali ions by hydrogen ions resulting in the
5 formation of hydrogen Feldspar; (2) Rapid build-up of sodium and depleted layer
enriched with Si and /or Al; and (3) Slow dissolution of the residual layer at the solidsolution interface accompanied by diffusion of ions from the fresh feldspar boundary.
Further, the rate of step (3) i.e. dissolution of the residual layer is controlled by
decomposition of activated surface complexes whose formations depends on pH
10 (alkaline or basic), the concentration of dissolved Al and sometimes on the Na
concentration especially in alkaline solution. In view of above observations (which
may be maintained in a correlation database), the diagenetic events at one or more
points depths throughout the selected range of sedimentary formation are evaluated
using data analysis on one or more of the following: determined environmental
15 conditions, anion concentration, elements and their concentration at respective point
depths. Assuming, potassium(K), sodium(Na), calcium(Ca) are the elements
determined at depth 3670m based on the analysis of leachates(obtained from core
sample of depth 3670m). The above combination of elements along with log K+ or log
H+ and Log Na (retrieved from correlation database) indicate the probability of
20 Feldspar. Assuming, the environmental conditions at depth 3670m are alkaline
(reducing) and the concentration of Na is relatively more than Si and/or Al, dissolution
of Feldspar is evaluated as the diagenetic event.
[0039] Example 4: Diagenetic Event- Clay mineral cementation
[0040] Clay minerals are the most common cementing materials in the
25 sandstones(sedimentary rocks). These minerals act as pore lining rim cement and porefilling matrix. Smectite, kaolinite and illite (with molecular composition as defined in
Table 1 below) are some of the major clay minerals that act as cementing agent in the
rocks. Said authigenic clay minerals are formed through recrystallization of fine matrix
and dissolution of K-feldspars. In addition, the aforementioned clay minerals may also
30 be formed due to modification or alteration of one kind of clay mineral to another, for
21
instance, both smectite and kaolinite can be transformed into illite. It has been
observed that Illite clay occurs as pore filling and at lining of clay minerals. Illitization
usually occurs after the precipitation of kaolinite and smectite, and requires influx of
potassium under a higher temperature. Authigenesis of illite clay depends on the
5 precipitation and alteration of smectite/kaolinite and other labile detrital minerals that
are easily altered and require alkaline (illite) and acidic (kaolinite) pore fluid. Further,
Kaolinite, smectite and illite cements can be differentiated based on respective
concentrations of calcium, sodium and potassium due to the variation in their
molecular formulas. The higher concentration of sodium and calcium shows the
10 presence of smectite, whereas enriched concentration of potassium results in illite
formations. Furthermore, during deposition of distributary channel sediments in the
deltaic front setting and in weak alkaline conditions concentration of iron and
magnesium decreases. This decrease in concentration of iron and magnesium aids in
smectite and kaolinite transformation into chlorite. Referring to figure 4 a graph
15 representing chlorite cementation as an event prevailing during diagenesis at one or
more depths of the sedimentary formation is shown.
Molecular formula of clay cements
Kaolinite Al2O3 2SiO2·2H2O
Illite (K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O)]
Smectite X.3·nH2O [(Al1.5Fe3+.2Mg.3) Si4O10(OH)2]−.3 (where X=exchangeable
cations such as Na+ and Ca2+; n=number of interlayer water molecules)
Table 1
[0041] In view of above observations (which may be maintained in a correlation
database), the diagenetic events at one or more points depths throughout the selected
20 range of sedimentary formation are evaluated using data analysis on the determined
environmental conditions, anion concentration, elements and their concentration at
respective point depths. As shown in figure 4, high concentration of iron and
magnesium at depths 3651m, 3834.90m and 3872.8m infers Kaolinite. Further, the
22
decrease in concentration of iron and magnesium at 3871m under weak alkali
conditions infer conversion of Kaolinite to chlorite.
[0042] Example 5: Diagenetic Event- Silica Cement
[0043] It is known that Quartz cement exists in rocks as a result of precipitation of
5 silica into the pore spaces between grains. Quartz cement occurs as both fine granular
quartz filling pore spaces and overgrowths in the rocks. This type of cement was
formed in the early diagenetic stage. The dissolution of feldspars and micas lead to the
release of silica, thus providing the silica source for the formation of quartz cement
and authigenic quartz. Further, it has been studied that quartz cement and authigenic
10 quartz precipitate in acidic environmental condition. In view of foregoing observations
(which may be maintained in a correlation database), the diagenetic events at one or
more points depths throughout the selected range of sedimentary formation are
evaluated using data analysis on the determined environmental conditions, anion
concentration, elements and their concentration at respective point depths.
15 [0044] At step 112, formation characteristics at respective point depths throughout the
selected depth range of sedimentary formation are assessed based on the identified
diagenetic events in view of the environmental conditions, elemental concentration,
and anionic concentration. In particular, the formation characteristics at respective
point depths throughout the selected depth range of sedimentary formation are
20 assessed based on the percentage of identified diagenetic events in view of the
environmental conditions, anionic concentration, and elements and their concentration
at respective point depths using data analysis. For example: Assuming that the pH of
water-based leachate obtained from core sample extracted from depth 3700m of the
sedimentary formation is 8, and Calcium cementation is the evaluated diagenetic event
25 at depth 3700m. pH of water-based leachate indicates that the nature of fluid at depth
3700m is alkaline, and as alkaline conditions favour Calcium cementation, this is
further indicative of decrease in porosity. Accordingly, the formation at depth 3700m
may be characterised as alkaline and non-porous. Further, the non-porous
characteristic of formation is indicative of low hydrocarbon potential at the point depth
30 of 3700m.
23
[0045] In another example: Assuming that the pH of water-based leachate obtained
from core sample extracted from depth 3600m of the sedimentary formation is 5, and
quartz overgrowth is the evaluated diagenetic event at depth 3600m. pH of water-based
leachate indicates that the nature of fluid at depth 3600m is acidic, and as acidic
5 conditions favour Quartz overgrowth provided silicon concentration is more than 95%,
this is further indicative of increase in porosity. Accordingly, the formation at depth
3600m is characterised as acidic and porous. Further, the porous characteristic of
formation is indicative of hydrocarbon potential and/or good quality of the formation
at the point depth of 3600m.
10 [0046] Advantageously, the method of the present invention facilitates evaluation of
physico-chemical conditions and events prevailing during diagenesis of sedimentary
rocks using an economical geochemical approach. The method of the present invention
further affords determination of nature of original fluid that prevailed during phases of
diagenesis, which along with physico-chemical conditions and events further enable
15 precise assessment of the hydrocarbon potential. Furthermore, the method of the
present invention offers wider applicability and is easy to implement.
[0047] While the exemplary embodiments of the present invention are described and
illustrated herein, it will be appreciated that they are merely illustrative. It will be
understood by those skilled in the art that various modifications in form and detail may
20 be made therein without departing from the scope of the invention except as it may be
described by the following claims.

We claim:
1. A method of evaluating physico-chemical conditions and events during
diagenesis at a depth of a sedimentary formation, the method comprising:
obtaining water-based leachate, strong acid-based leachate and acetic acid
5 based leachate by leaching a core sample from the depth of the sedimentary
formation in water, strong acid composition and acetic acid, respectively;
determining environmental conditions, anionic concentration, and
elements and concentration of the elements at the depth based on an analysis of
the obtained water-based leachate;
10 individually determining elements and concentration of the elements at the
depth based on an analysis of the obtained strong acid-based leachate and the
acetic acid based leachate; and
evaluating events prevailing during diagenesis at the depth along with the
percentage of occurrence of said events based on the environmental conditions,
15 the anionic concentration, and the elements and the concentration of the elements
corresponding to said depth determined individually based on the analysis of the
water-based leachates, the strong acid-based leachates and the acetic acid based
leachates.
2. The method as claimed in claim 1, wherein the core sample is extracted
20 from a depth within a selected depth range of the sedimentary formation.
3. The method as claimed in claim 1, wherein obtaining the water-based
leachate by leaching the core sample in the water comprises:
drying and grinding the core sample;
leaching 1gm of the dried and grinded core sample in 5 ml of the water to
25 obtain a solution of the core sample and the water;
allowing the solution formed from the core sample and the water to settle
for 24 hours; and
25
obtaining water-based leachate by filtering the solution.
4. The method as claimed in claim 3, wherein the water is distilled water
having pH in the range of 6.0-7.5.
5. The method as claimed in claim 1, wherein obtaining the strong-acid
5 based leachate by leaching the core sample in the strong acid composition
comprises:
drying and grinding the core sample;
adding 0.15g of the dried and grinded core sample in 10ml strong acid
composition and drying on a hot plate at 170 0
C to obtain a dry end-product;
10 dissolving the dry end-product in 2% HNO3; and
obtaining the strong acid-based leachate by filtering aliquot of solution
formed from the dry end-product dissolved in 2% HNO3.
6. The method as claimed in claim 1 or 5, wherein the strong acid
composition comprises Nitric acid (HNO3), Perchloric acid (HClO4) and Hydrogen
15 Fluoride (HF) in the ratio of 3:3:4.
7. The method as claimed in claim 5, wherein the aliquot is filtered using
Whatman 42 filter paper.
8. The method as claimed in claim 1, wherein obtaining the acetic acid
based leachate by leaching the core sample in the acetic acid comprises:
20 drying and grinding the core sample;
adding 100mg of the dried and grinded core sample to 3ml of 0.3% acetic
acid solution, and allowing to settle for 24 hours;
filtering an aliquot of solution formed from the core sample dissolved in
acetic acid; and
26
drying the filtered aliquot and dissolving in 2(N)HCl to obtain acetic acid
based leachate.
9. The method as claimed in claim 8, wherein the aliquot is filtered using
Whatman 42 filter paper and the acetic acid is freshly prepared glacial acetic acid.
5 10. The method as claimed in claim 1, wherein determining the
environmental conditions at the depth based on the analysis of the obtained waterbased leachate comprises estimating pH of the water-based leachate using pH
meter, wherein the determined pH is indicative of oxidizing or reducing
environment conditions around the depth of the sedimentary formation wherefrom
10 the core sample is extracted for obtaining the water-based leachate.
11. The method as claimed in claim 1, wherein determining the anionic
concentration, the elements and the concentration of the elements at the depth
based on the analysis of the obtained water-based leachate comprises determining
anionic concentration, elements and concentration of the elements in the water15 based leachate, wherein the determined the anionic concentration, the elements
and the concentration of the elements in the water-based leachate is indicative of
the anionic concentration, the elements and the concentration of the elements at
the depth of the sedimentary formation wherefrom the core samples is extracted
for obtaining the water-based leachate.
20 12. The method as claimed in claim 1, wherein determining the elements
and the concentration of the elements at the depth based on the analysis of the
obtained strong acid-based leachate comprises:
subjecting the obtained strong acid-based leachate to Inductively Coupled
Plasma - Optical Emission Spectrometry (ICP-OES) and analysing for
25 determining elements and concentration of the elements in the strong acid-based
leachate, wherein the determined elements and the concentration of the elements
in said strong acid-based leachate is indicative of the elements and concentration
of the elements at the depth wherefrom the core sample was extracted.
27
13. The method as claimed in claim 12, wherein the strong-acid based
leachate is analysed for elements including iron(Fe), Magnesium(Mg),
Aluminium(Al), sodium(Na), potassium(K), calcium(Ca), Zinc(Zn),
Manganese(Mn), Vanadium(V), Titanium(Ti), Strontium(Sr), Rubidium(Rb),
5 Uranium(U), Copper(Cu), Nickel(Ni), Cobalt(Co), Chromium(Cr),
Phosphorus(P), Cerium(Ce), Dysprosium(Dy), Erbium(Er), Europium(Eu),
Gallium(Ga), Holmium(Ho), Lanthanum(La), Lutetium(Lu), Neodymium(Nd),
Praseodymium(Pr), scandium (Sc), samarium(Sm), Terbium(Tb), Thorium(Th),
Thulium(Tm), Yttrium(Y), and Ytterbium(Yb).
10 14. The method as claimed in claim 1, wherein determining the elements
and concentration of the elements at the depth based on the analysis of the
obtained acetic acid based leachate comprises:
subjecting the obtained acetic acid based leachate to Inductively Coupled
Plasma - Optical Emission Spectrometry (ICP-OES) and analysing for
15 determining elements and concentration of the elements in the acetic acid based
leachate, wherein the determined elements and the concentration of the elements
in said acetic acid based leachate is indicative of the elements and concentration
of the elements at the depth wherefrom the core sample was extracted.
15.The method as claimed in claim 14, wherein the acetic acid based
20 leachate is analysed for 6 elements including iron(Fe), Magnesium(Mg),
Aluminium(Al), sodium(Na), potassium(K), and calcium(Ca)
16.The method as claimed in claim 1, wherein the events prevailing during
diagenesis at the depth along with the percentage of occurrence of said events are
evaluated based on the environmental conditions, the anionic concentration, and
25 the elements and the concentration of the elements corresponding to said depth
determined individually based on the analysis of the water-based leachates, the
strong acid-based leachates and the acetic acid based leachates using data analysis
techniques, wherein the data analysis techniques are based on predetermined
correlations between various elements and anions in view of environmental
30 conditions.
28
17.The method as claimed in claim 1, wherein the events prevailing during
diagenesis at the depth along with the percentage of occurrence of said events are
evaluated based on the environmental conditions, the anionic concentration, and
the elements and the concentration of the elements corresponding to said depth
5 determined individually based on the analysis of the water-based leachates, the
strong acid-based leachates and the acetic acid based leachates using data analysis
techniques in conjunction with a predefined correlation database, wherein the
predefined correlation database comprises information regarding elements,
chemical relationship of said elements with respect to each other in varying
10 conditions, chemical reactions between one or more elements and anions in
presence of other elements and anions, probable chemical processes and paleoweathering patterns in view of various elements and relative variation of elements
with respect to other elements, and well logs associated with the sedimentary
formation.
15 18.The method as claimed in claim 1, wherein evaluating the events
prevailing during diagenesis at the depth along with the percentage of occurrence
of said events based on the environmental conditions, the anionic concentration,
and the elements and the concentration of the elements corresponding to said depth
determined individually based on the analysis of the water-based leachates, the
20 strong acid-based leachates and the acetic acid based leachates comprises:
evaluating one or more minerals at the depth by correlating the elements
and the concentration of the elements determined based on the water-based
leachates, the strong acid-based leachates and the acetic acid based leachates in
view of the environmental conditions and the anionic concentration using data
25 analysis or a correlation database or a combination of data analysis and the
correlation database; and
evaluating the events prevailing during diagenesis at the depth along with
the percentage of occurrence of said events based on the evaluated one or more
minerals or the concentration of elements or a combination thereof in view of the
30 environmental conditions at the depth using data analysis.
29
19.The method as claimed in claim 1, wherein the events prevailing during
diagenesis include physical processes, chemical processes, and biochemical and
organic processes.
20.The method as claimed in claim 18, wherein the step of evaluating the
5 one or more minerals at the depth comprises: evaluating one or more probable
mineral compositions at the depth by correlating the elements determined based on
the analysis of water-based leachate, strong acid-based leachate and acetic acid
based leachate in view of the environmental conditions and/or the anionic
concentration at the depth using data analysis and/or correlation database; and
10 correlating the evaluated one or more probable mineral compositions with
the concentration of the elements and anions forming said probable mineral
compositions to evaluate the one or more minerals at the depth.