FIELD OF THE INVENTION
[oooi] The present invention generally relates to fracture completion strategies and,
more specifically, to optimizing the placement of fracture intervals based upon a
mineralogical analysis of the formation.
BACKGROUND
100021 Conventionally, a very simplistic approach is used to determine fracture
initiation points along a wellbore. The first fracture point is selected at random or based
upon gas shows encountered while drilling (with weight given to low gamma sections), and
the subsequent fracture points are evenly spaced apart from one another. This approach is
based on the assumption that there is very little geological and mineralogical variation
along the length of the wellbore. Although this is a simple and easy method for distributing
the fracture treatments equally along the wellbore, it does nothing to target potentially
productive intervals. Instead, operators almost blindly choose fracture points with no
consideration for sound engineering. As a result, roughly 40% of completion clusters never
produce hydrocarbons.
10003] Accordingly, in view of the foregoing shortcomings, there is a need in the
art for a fracture completion strategy which utilizes sound engineering to enable operators
to select optimal fracture intervals, thereby increasing the efficiency of fracture placement
and improving well production.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 illustrates a block diagram representing a fracture optimization
system according to an exemplary embodiment of the present invention;
[0005] FIG. 2 illustrates a flow chart representing a method for fracture
optimization according to an exemplary methodology of the present invention;
[0006] FIG. 3 illustrates a fracture optimization log according to an exemplary
embodiment of the present invention; and
[0007] FIG. 4 illustrates a fracture optimization log according to an alternative
exemplary embodiment of the present invention.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
10008] Illustrative embodiments and related methodologies of the present invention
are described below as they might be employed in a system for optimizing fracture
completion strategies. In the interest of clarity, not all features of an actual implementation
or methodology are described in this specification. It will of course be appreciated that in
the development of any such actual embodiment, numerous implementation-specific
decisions must be made to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary from one implementation
to another. Moreover, it will be appreciated that such a development effort might be
complex and time-consuming, but would nevertheless be a routine undertaking for those of
ordinary skill in the art having the benefit of this disclosure. Further aspects and
advantages of the various embodiments and related methodologies of the invention will
become apparent from consideration of the following description and drawings.
|0009| FIG. 1 shows a block diagram of fracture optimization system 100 according
to an exemplary embodiment of the present invention. In one embodiment, fracture
optimization system 100 includes at least one processor 102, a non-transitory, computerreadable
storage 104, transceiver/network communication module 105, optional I/O
devices 106, and an optional display 108, all interconnected via a system bus 109.
Software instructions executable by the processor 102 for implementing software
instructions stored within fracture optimization module 110 in accordance with the
exemplary embodiments described herein, may be stored in storage 104 or some other
computer-readable medium.
[ooio] Although not explicitly shown in Fig. 1, it will be recognized that fracture
optimization system 100 may be connected to one or more public and/or private networks
via appropriate network connections. It will also be recognized that the software
instructions comprising the fracture optimization module 110 may also be loaded into
storage 104 from a CD-ROM or other appropriate storage media via wired or wireless
means.
[ooii] Referring to the exemplary methodology of FIG. 2, it will now be described
how fracture optimization system 100 utilizes mineralogy to develop a log that facilitates
optimal placement of fracture intervals. In general, mineralogy may be defined as the study
of the chemistry, structure, and physical properties of minerals. At step 202, processor 102,
utilizing formation optimization module 110, calibrates the mineralogical analysis. In
order to accomplish the calibration, the formation is cored along the wellbore. Samples are
then taken as desired throughout the core and analyzed, typically, using a Induce Couple
Plasma Spectroscopy/Mass Spectroscopy ("ICP"). Another set of core samples are then
analyzed using, for example, a Spectros X-Ray florescence ("XRF") instrument or a Laser
Induced Breakdown Spectroscopy ("LIB") instrument, dependent upon the type of data
desired. In this exemplary embodiment, core samples are taken every 1.5 feet. Utilizing
chemostratigraphy, processor 102 then correlates the ICP data to the XRF or LIB data
across the cored interval, thereby determining the elements and the concentrations of the
major and minor elements/compounds of the core samples, as would be understood by one
ordinarily skilled in the art having the benefit of this disclosure. As described below, this
information plus ratios of elements are used to determine and model clay content, relative
brittleness index ("RBI"), redox metals, and elevated factor redox metals ("EFRM").
[0012] During testing of the present invention, analyzed core results identified eight
beds where the clay content was greater than 15% and four beds where the clay content was
greater than 30%. Based upon this, it was discovered there is a direct correlation between
the EFRM (e.g., elevated factor vanadium, uranium, nickel, cobalt, copper, chromium, etc.)
values and the clay content in wellbores. As a result, it was shown that EFRM equals the
number of times that a redox metal is enriched over the average redox metal content in a
Post Archean Australian Shale ("PAAS"), which is standardized to aluminum using the
following equation:
Equation 1.1: EFRM (RMV/Al(Sample))/(RM/Al(PAAS))
oo j Furthermore, test data showed that EFRM is a relative indicator of total
organic carbon, which implies the presence of hydrocarbons. Also, RBI values get lower as
clay content increases, which indicates a more ductile environment.
[0014] After calibration is complete at step 202, formation samples are collected
during drilling of the wellbore at step 204. In this exemplary embodiment, measured while
drilling ("MWD") and mudlogging methods may be utilized to retrieve and analyze the
cutting samples from which elemental information will be derived. Also, the samples may
be taken at a desired capture rate in the vertical or horizontal sections of the wellbore. For
example, a sample capture rate of every 20 to 30 feet is typical in the horizontal section of
the wellbore. After collection, the cutting samples are sieved, rinsed with solvents to
remove as much drilling mud as possible, and a magnet is used to clean out any metal that
may have found its way into the sample during the drilling process. In this exemplary
embodiment, the analysis is performed on-site to assist with directional drilling. However,
as would be understood by one ordinarily skilled in the art having the benefit of this
disclosure, the analysis may be performed off-site as well. Thereafter, the samples are
then dried, weighed, crushed, and pelletized.
10015] At step 206, processor 102 analyzes the samples utilizing the necessary
instrumentation, such as XRF, in order to determine the elements which make up the
pelletized samples. At step 208, processor 102 utilizes the elemental data to generate the
log data. The resulting elemental data, such as nickel, copper, vanadium or other redox
metals, indicates carbon rich zones. For example, if vanadium was found in high
concentrations in the formation, an elevated factor vanadium ("EFV") would be calculated.
If you have more than one redox metal present in high concentrations, one or both may be
selected. Thus, at step 208(a), processor 102 utilizes one of the redox metals, vanadium, to
determine the EFV (used in place of EFRM), using Equation 1.1, where V equals the
vanadium content of the sample determined using the XRF instrumentation. If the EFV is
greater than 1, this indicates an environment where hydrocarbons are being produced. If
EFV is over 10, this indicates a strong producing zone. Accordingly, a tiered ranking
system could be employed which identifies poor, moderate, and strong producing intervals,
as would be understood by one ordinarily skilled in the art having the benefit of this
disclosure.
[0016] At step 208(b), processor 102 generates a gamma log based on the uranium
content of the pelletized sample. Here, the gamma data received during drilling is
correlated against wireline data to determine if shifts in depth are necessary. Next,
processor 102 generates the spectra gamma (potassium, thorium, and uranium), which
indicates the presence of volcanic ash. If volcanic ash is present, this indicates an
undesirable fracturing point. At step 208(c), processor 102 models the clay content and
breaks it down into total clay and illite clay. During testing of the present invention, it was
discovered that high total clay content zones do not produce well. Next, processor 102
determines the mineralogy (208(d)), RBI (208(e)), gas values (208(f)) and ROP (208(g)).
Those ordinarily skilled in the art having the benefit of this disclosure realize there are a
variety of means by which the log data determined in step 208 may be modeled and/or
generated.
[0017] At step 210, processor 102 utilizes the correlated data to generate and
output a fracture optimization log of the wellbore, which will be used to determine the
optimal fracture initiation intervals. In an alternative embodiment, processor 102 may also
correlate the generated log data to wireline data, particularly in new basins, if confirm data
integrity.
00 ] FIG. 3, illustrates a fracture optimization log 300 produced by fracture
optimization system 100 (step 210) according to an exemplary embodiment of the present
invention. Column 302 plots the wellbore track, which is used to show the inclination of
the borehole. Column 304 plots an end-user's naming convention for the various rock
layers and formations (i.e., lithologic markers), which provides a correlation between two
different units (e.g., to show correlation between proprietary lithologic units and the
standard chemostratigraphic units). Column 306 plots the chemostratigraphic units, which
are the units used to define layers of chemically similar rock. Column 308 plots the gamma
and chemo-gamma overlay on a scale of 0-150 API in order to determine sample lag
accuracy, depth tie-in to other logs and fracture placement, sample quality and borehole
conditions.
[0019] In further reference to FIG. 3, column 310 plots the uranium, potassium, and
thorium (spectra gamma) data on a scale of 0-100 API, which is used to define the
continental source rock (typically volcanic ash) which can reflect a high clay content and,
thus, a potential drilling hazard. Column 312 plots the redox metals, which indicate total
organic carbon content, as discovered during testing of the present invention; thus, the
presence of redox metals indicate highly organic rich zones. In this exemplary
embodiment, nickel and uranium are used as the redox metals because the exemplary
wellbore comprised these metals. However, those ordinarily skilled in the art having the
benefit of this disclosure realize that different formations would comprise different redox
metals that would indicate the presence of carbons. Nickel is plotted on a scale of 0-20,
while uranium is plotted on a scale of 0-4.
10020] Column 314 plots the illite clay content on a scale of 0-40%, which is used
to determine the illite-smectite fraction of the sediment. When the illite clay content is
compared to the XRD data, it indicates the swelling potential of the clay in the formation.
In this exemplary embodiment, the actual illite clay content percentage is listed along the
plotted line, thus making it easier to determine the respective percentage at any given
depth. Column 316 plots the total clay and EFV, which are used to determine the total clay
content percentage of the rocks and vanadium content (also indicative of a depositional
environment). Total clay is measured plotted on a scale of 0-40%, while EFV is plotted on
a scale of 1-25. In this exemplary embodiment, the total clay percentage value is listed
along the plotted line, thus making it easier to determine the respective percentage at any
given depth. Column 318 plots the RBI on a scale of 70-100, a calculated curve that
indicates the fracability along the rock formation. In general, as discovered during testing
of the present invention, a higher RBI indicates increased fracturing potential.
10021] Column 320 plots the mineralogy of the formation cuttings along a scale of
0-100. Box 321 includes a listing of all the minerals plotted along column 320, along with
their color-coded indicators. However, other indicators may be utilized to distinguish one
mineral plot line from another, as would be understood by persons ordinarily skilled in the
art having the benefit of this disclosure. Column 322 plots the C1-C5 gas values receives
from the mudloggers, each plotted on a scale of 0.1-100. Column 324 plots the MWD rate
of penetration ("ROP") along with the mudloggers total hydrocarbon gas. ROP is plotted
on a scale of 0-300 ft/hr, while the total gas units are plotted on a scale of 0-2500.
[0022] FIG. 4 illustrates fracture optimization log 400 produced by fracture
optimization system 100 according to an alternative exemplary embodiment of the present
invention. Essentially, fracture optimization log 400 is a simplified version of fracture
optimization log 300 that only plots the drilling gamma ray data 402, total clay content 404,
redox metal 406, illite clay 408, and RBI 410. In this embodiment, redox metal 406 is
reflected as EFV. The gamma ray data 402 is plotted on a scale of 0-150 API, total clay
404 and illite clay 408 on a scale of 0-100%, EFV on a scale of 0-25, and the RBI on a
scale of 70-100. However, as previously mentioned, other formations may contain other
redox metals which may be utilized instead. Moreover, one of ordinary skill in the art
having the benefit of this disclosure realizes that the scales and ranges utilized in fracture
optimization logs 300,400 may be altered as necessary.
[0023] As previously stated, the optimal fracture interval locations are determined
through utilization of the mineralogical information contained in formation optimization
logs 300 & 400. In exemplary embodiments, the primary parameters that are utilized in
this determination are the RBI, the EFV, and the total clay. In other embodiments,
however, other redox metals may be utilized such as, for example, uranium, nickel, copper,
cobalt, chromium, etc. Also, fracture optimization log 300 includes additional information
to aid geologists in gaining a deeper understanding of the wellbore characteristics.
10024) Through testing of the present invention, it has been discovered that
intervals having a high RBI, high EFRM, and low clay are most desirable ("optimization
criteria"). Fracture intervals meeting these criteria are easy to initiate, plus their high RBI
results in their ability to generate moderate fracture complexity. High EFRM values are to
be targeted, as they infer the presence of hydrocarbons, while low clay content is also
preferred to minimize the possibility of losing the connectivity between the fracture and the
wellbore due to clay swelling and embedment (resulting in a choked fracture).
002 1 Accordingly, after fracture optimization logs 300 & 400 have been produced
by fracture optimization system 100 (step 210), an end-user (field personnel, etc.) may
review the log to determine the most optimal location for the fracture intervals. The
operator would then review logs 300,400 to identify those intervals, and their respective
depths, which have high RBI and EFRM values, and low total clay content. For example,
referring to formation optimization log 400, target interval 412 meets these criteria.
Therefore, this interval should be primarily targeted for fracturing operations. Other
intervals meeting the optimized criteria may then be targeted in a tiered approach or as
otherwise desired.
[0026] In an alternate exemplary embodiment of the present invention, fracture
optimization system 100 may itself determine the most optimal location for fracture
intervals based on the data plotted in fracture optimization logs 300 & 400. Here,
processor 102, utilizing fracture optimization module 110, will analyze the data plotted in
fracture optimization logs 300 & 400 at step 210. Thereafter, processor 102 will determine
those intervals which meet the optimization criteria, and output the results. The result may
be output in a variety of forms, such as, for example, formation optimization logs 300 &
400 may include an extra column which indicates the optimal fracture locations and their
respective depths or this information may be outputted in a stand alone report. Moreover,
the identified intervals may be identified in a tiered format such as, for example, poor,
moderate, and strong producing intervals.
[0027] Although various embodiments and methodologies have been shown and
described, the invention is not limited to such embodiments and methodologies and will be
understood to include all modifications and variations as would be apparent to one skilled
in the art. Therefore, it should be understood that the invention is not intended to be
limited to the particular forms disclosed. Rather, the intention is to cover all modifications,
equivalents and alternatives falling within the spirit and scope of the invention as defined
by the appended claims.

CLAIMS
WHAT I CLAIM IS:
1. A computer-implemented method to determine placement of fracture initiation
points along a wellbore, the method comprising:
(a) analyzing formation samples of one or more intervals along the wellbore;
(b) determining a total clay content, elevated factor redox metal, and relative
brittleness index of the formation samples; and
(c) outputting a fracture optimization log which plots the total clay content,
elevated factor redox metal, and relative brittleness index of the one or more
intervals along the wellbore,
wherein the placement of the fracture initiation points is determined based upon the
fracture optimization log.
2. A computer-implemented method as defined in claim 1, wherein the redox metal is
at least one of vanadium, uranium, nickel, copper, cobalt, or chromium.
3. A computer-implemented method as defined in claim 1, wherein step (b) further
comprises determining at least one of a gamma ray, rate of penetration, or illite clay content
of the formation samples.
4. A computer-implemented method as defined in claim 3, wherein step (c) further
comprises outputting a fracture optimization log which also plots at least one of the gamma
ray, rate of penetration, or illite clay content of the one or more intervals along the
wellbore.
5. A computer-implemented method as defined in claim 1, further comprising:
determining the placement of the fracture initiation points along the wellbore based
upon the fracture optimization log; and
outputting the determined fracture initiation points.
6. A computer-implemented method as defined in claim 5, wherein the step of
determining the placement of the fracture initiation points further comprises determining
which intervals comprise a high relative brittleness index, high elevated factor redox metal,
and low total clay content.
7. A computer-implemented method as defined in claim 2, wherein the one or more
intervals comprising a high relative brittleness index, high elevated factor redox metal, and
low total clay content are determined to be the fracture initiation points.
8. A system comprising processing circuitry to determine placement of fracture
initiation points along a wellbore, the processing circuitry performing the steps of:
(a) analyzing formation samples of one or more intervals along the wellbore;
(b) determining a total clay content, elevated factor redox metal, and relative
brittleness index of the formation samples; and
(c) outputting a fracture optimization log which plots the total clay content,
elevated factor redox metal, and relative brittleness index of the one or more
intervals along the wellbore,
wherein the placement of the fracture initiation points is determined based upon the
fracture optimization log.
9. A system as defined in claim 8, wherein the redox metal is at least one of vanadium,
uranium, nickel, copper, cobalt, or chromium.
10. A system as defined in claim 8, wherein step (b) further comprises the step of
determining at least one of a gamma ray, rate of penetration, or illite clay content of the
formation samples.
11. A system as defined in claim 10, wherein step (c) further comprises the step of
outputting a fracture optimization log which also plots at least one of a gamma ray, rate of
penetration, or illite clay content of the one or more intervals along the wellbore.
12. A system as defined in claim 8, further comprising the steps of:
determining the placement of the fracture initiation points along the wellbore based
upon the fracture optimization log; and
outputting the determined fracture initiation points.
13. A system as defined in claim 12, wherein the step of determining the placement of
the fracture initiation points further comprises the step of determining which intervals
comprise a high relative brittleness index, high elevated factor redox metal, and low total
clay content.
14. A system as defined in claim 9, wherein the one or more intervals comprising a
high relative brittleness index, high elevated factor redox metal, and low total clay content
are determined to be the fracture initiation points.
15. A computer program product comprising instructions which, when executed by at
least one processor, causes the processor to perform a method comprising the steps of:
(a) analyzing formation samples of one or more intervals along a wellbore;
(b) determining a total clay content, elevated factor redox metal, and relative
brittleness index of the formation samples; and
(c) outputting a fracture optimization log which plots the total clay content,
elevated factor redox metal, and relative brittleness index of the one or more
intervals along the wellbore,
wherein placement of fracture initiation points is determined based upon the
fracture optimization log.
16. A computer program product as defined in claim 15, wherein the redox metal is at
least one of a vanadium, uranium, nickel, copper, cobalt, or chromium.
17. A computer program product as defined in claim 15, wherein step (b) further
comprises the step of determining at least one of a gamma ray, rate of penetration, or illite
clay content of the formation samples.
18. A computer program product as defined in claim 17, wherein step (c) further
comprises the step of outputting a fracture optimization log which also plots at least one of
a gamma ray, rate of penetration, or illite clay content of the one or more intervals along the
wellbore.
19. A computer program product as defined in claim 15, further comprising the steps
of:
determining the placement of the fracture initiation points along the wellbore based
upon the fracture optimization log; and
outputting the determined fracture initiation points.
20. A computer program product as defined in claim 19, wherein the step of
determining the placement of the fracture initiation points further comprises the step of
determining which intervals comprise a high relative brittleness index, high elevated factor
redox metal, and low total clay content.
21. A computer program product as defined in claim 16, wherein the one or more
intervals comprising a high relative brittleness index, high elevated factor redox metal, and
low total clay content are determined to be the fracture initiation points.
22. A method to determine placement of fracture initiation points along a wellbore, the
method comprising:
(a) analyzing mineralogical characteristics of one or more intervals along the
wellbore; and
(b) determining the placement of the fracture initiation points based upon the
mineralogical characteristics of the one or more intervals along the wellbore.
23. A method as defined in claim 22, wherein step (b) further comprises determining
which of the one or more intervals comprise a high relative brittleness index, high elevated
factor redox metal, and low total clay content.
24. A method as defined in claim 22, wherein step (b) further comprises creating a log
which plots the mineralogical characteristics of the one or more intervals along the
wellbore, the placement of the fracture initiation points being determined based upon the
log.
25. A method as defined in claim 24, wherein the one or more intervals comprising a
high relative brittleness index, high elevated factor redox metal, and low total clay content
are determined to be the fracture initiation points.
26. A method as defined in claim 22, further comprising ranking the one or more
intervals based upon production capability as determined by the mineralogical
characteristics.
27. A method as defined in claim 22, wherein the mineralogical characteristics are a
elevated factor redox metal or a total clay content.
28. A method as defined in claim 25, wherein the high elevated factor redox metal is at
least one of a vanadium, nickel, chromium, cobalt, copper, or uranium.