FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
THE PATENTS RULES, 2003
Provisional/ Complete specification
[See section 10 and rule 13]
1. Title of invention:
"Improving Solvent Efficiency By Doping Polymer 'Dispersant' To Mitigate Asphaltene Precipitation".
2. Applicant(s):
Name Nationality Address
Oil and Natural Gas India IOGPT, Phase -II, Panvel -
Corporation Ltd. 410221, Navi Mumbai,
Maharashtra, India.
3. Preamble to the description:
The following specification particularly describes the invention and the manner in which it is to be performed.

IMPROVING SOLVENT EFFICIENCY BY DOPING POLYMER 'D1SPERSANT TO MITIGATE ASPHALTENE PRECIPITATION
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a solvent composition which is particularly used to dissolve and remove down hole Asphaltene precipitates and clean up the organic debris. Doping the aromatic solvent with a dispersant, Alkyl phenol ploy ethanoxy ether, effectively solubilize the asphaltene compounds and improve significantly down hole cleaning efficiency. The invented formulation enhances over all efficiency of the solvent and reduces pressure drop across the well bore.
2. Description Of The Prior Art:
Asphaltenes are high molecular weight nitrogen, sulphur and oxygen containing compounds. The current popular belief is that they represent an intermediate product between kerogen and oil - a soluble low molecular weight kerogen. There is no implied genetic relationship between resins and asphaltenes- resins may polymerise to form asphaltenes and asphaltenes may break down in to resins. Asphaltenes may be dispersed in the crude oils by the action of resins. The polar resin molecules may form micelles with Asphaltene molecules creating nucleus. In a resin poor environment micelles may form multiple Aphaltene molecules, as a result of these physico-chemical shifts, the chemistry of Asphaltenes is extremely difficult to establish. Petroleum may be considered to be an equilibrium mixture of different chemical

compounds. Modification of the chemical composition of the petroleum either under natural conditions or in the laboratory leads to a shift, back towards the equilibrium composition. Thus cracking of petroleum in the reservoir due to thermal stress causes a shift towards light saturated hydrocarbons and Asphaltene precipitation occurs. The same effect in the laboratory is created by the addition of light hydrocarbon (N-Heptane). The Asphaltene fraction of a crude oil is hence defined by the solvent normally pentane, hexane or heptane chosen to 'displace' the Asphaltenes from the oil. This equilibrium may be disturbed during production of oil leading lo precipitation of Asphaltenes in the pore spaces of a reservoir rock.
Precipitation in reservoirs, wells and surface facilities has a severe detrimental effect on the economics of oil production because of a reduction in well productivity and / or clogging of the production facilities.
As stated earlier, the nature and behavior of Asphaltenes in crude oil is complex. It is generally accepted that resins and maltenes (structures that are comparable with asphaltenes but with a much lower molecular weight) are responsible for keeping the Asphaltene particles in dispersion. The Asphaltenes are surrounded by the polar head groups of the resins and maltenes while the non-polar alkyl tails interact with the oil phase. Therefore, crudes with a high ratio of resins to asphaltenes are less subject to Asphaltene deposition than crudes with large amounts of non polar saturates compared with aromatics, which are more prone to exhibit Asphaltene precipitation problems. At "normal" reservoir conditions, the Asphaltenes, Resins, Maltenes,-and oil phase are in thermodynamic equilibrium. This equilibrium can be disturbed by a number of factors: decline of the reservoir pressure toward the bubble point, change in temperature, or addition of a

miscible solvent to the oil as applied in various jobs. Several solutions to this problem are known. One is physical removal of deposits through bailing, drilling, hydro blasting, or scraping. Ultrasonic-treatment techniques are also proposed, that breakup the asphaltene aggregates and thereby reduces its viscosity. Soaks with aromatic solvents and treatments with polymeric dispersant that inhibit the asphaltene flocculation are the two most widely used methods. This last method is believed to have characteristics in common with petroleum resins and interact with Asphaltenes and oil in a similar manner. The invented solvent along with asphalting dispersant is the subject of this Patent.
The reasons for the Asphaltene deposition can be many factors including variations of temperature, pressure, composition, flow regime, and wall and electro kinetic effect. When various heavy organic compounds are present in a petroleum fluid their interactive effects must be also considered in order to understand the mechanisms of their collective deposition. This is especially important when one of the interacting heavy organic compounds is Asphaltene. For example a regular waxy crude containing minute amounts of Asphaltene will behave differently at low temperatures (below the wax cloud point) compared to a clean waxy crude with no other heavy organics present in it. Considering that the major barrier in a profitable deposition-free oil production scheme is the presence of asphaltene in the crude in what follows the in situ role.
Asphaltenes are lyophilic with respect to aromatics, in which they form highly scattered colloidal solutions. Specifically, Asphaltenes of. low molecular weight are lyophobic with respect to paraffins like pentanes and petroleum crudes.

Asphaltene particles can assume various forms when mixed with other molecules depending on the relative sizes and polarities of the particles present. Thus, asphaltene particles are believed to exist in oil partly dissolved and partly in colloidal and / or micellar form. Whether the asphaltene particles are dissolved in crude oil, in steric colloidal state or in micellar form, depends, to a large extent, on the presence of other particles (paraffins, aromatics, resins, etc.) in the crude.
It is generally accepted that crude oil is considered to be a colloidal system comprising fractions of Saturates, Asphaltenes, Resins, and Aromatics. Asphaltene fractions are defined as dispersed colloids in the oil phase and are stabilized, to some extent, by the resin molecules that act as protective bodies for asphaltene particles. Colloidal asphaltenes can be naturally or artificially precipitated if the resins' protective shield is removed from asphaltene-particle surfaces. Asphaltene precipitation can occur in different parts of the production system including in the well tubing, the surface flow lines, and even the near-well bore reservoir. Asphaltene precipitation and deposition in oil-production systems depend on the changes in flow conditions, such as pressure, temperature, and oil composition. The factor that plays a major role in asphaltene problems under flow conditions is well-flow pressure behavior. This pressure controls the well-flow regime within the production system. In tubing, as the well fluid moves vertically, flow-regime change takes place, complicating the multiphase flow, which may cause severe asphaltene flocculation and deposition. This phenomenon can decrease well and, potentially, reservoir productivity, as well as increase production costs by requiring frequent chemical treatments for the removal of asphaltenes.
It has been observed that asphaltene deposition problem in the well tubing and near well bore increased significantly. This may be due to

changes in reservoir pressure with time and the increased gas/oil ratio (GOR). The latter has been shown to be an important factor in Asphaltene - particle flocculation in production systems.
2.1. Colloidal instability in reservoirs:
Destabilization (i.e., flocculation) of colloidal asphaltenes in oil-production systems principally depends on breaking up the balance of attraction forces between the adsorbed resin molecules and asphaltene particles. The principal causes of flocculation (aggregation) are the van der Waals attraction forces between particles, which are long-range forces. To counteract these forces and promote stability, equal long-range repulsive forces are required, as in the case of a steric effect caused by the aliphatic tails of resin molecules adsorbed on asphaltene particles. One of two mechanisms will occur after the aggregation process-either flotation or precipitation. For solid particles to float on the surface of a liquid, the total upward pull of the liquid around it must balance the apparent weight of the particles. To state an example, asphaltene particles float on crude oil and then precipitate by the addition of alkane solvents when the particles' apparent weight exceeds the liquid's upward pull forces. The growth of the particles' apparent weight (i.e., particle size) will depend on the continuation of the flocculation process, which, in turn, depends on the solvency power and/or the concentrations of the solvent. Both processes can accelerate the adsorption/deposition mechanisms on available rock/ pipe surfaces. Main factor that effects the stabilizing forces between Asphaltenes and resins is the change in crude oil composition. The natural state of Asphaltenes in petroleum fluids is described as a colloidal system stabilized, to some extent, by resins that act as peptizing agents. Destabilization of colloidal Asphaltenes appears to happen as a result of changes in temperature, pressure, and composition during primary

depletion. Heera field is being operated near the bubble point pressure (Pb-1800 psi, Pwf-1500 psi), the conditions are favorable to the onset of Asphaltene precipitation and it may significantly affect the production efficiency of a reservoir during oil recovery.
Present invention relates to the detailed studies on the problem and identified the areas for improvement of the existing solvent formulation. Colloidal instability Index (Cll) calculated on the basis of SARA analysis, indicate maximum Asphaltene problem in phase-Ill of Heera followed by South Heera and Main Heera field. SIMDIS analysis shows that carbon atom distribution is maximum at C11 and C12 which further supports the possibility of Asphaltene precipitation.
Asphaltene solubility studies on the crude samples with various combination of solvents, with and without dispersant have been carried out. Substantial improvement in asphaltene solubility is observed in case of solvent with a suitable dose of Dispersant 'Alkyf phenol Poly Ethanoxy Ether'. Core flow studies using a mixture of Xylene, Toluene, Naphthalene and suitable dose of dispersant, show significant improvement in the rock permeability and reduced pressure drop in the fluid flow. Dispersant impregnated solvent wash of asphaltene damaged core facilitates easy removal of adsorbed asphaltenes from the rock surface.
3. DETAILED DESCRIPTION OF THE INVENTION:
In petroleum production initially it is necessary to take any number of steps to prevent the deposition problem. If the problem of heavy organics precipitation can be eliminated by modification of the production practices, rather than by chemical or mechanical means, the

cost of production can be reduced appreciably. This can be achieved by proper laboratory tests, development of deposition prediction models, and design of the oil production and transportation systems accordingly. The organic debris generated at the bottom hole and in the tubing requires to be cleaned by an efficient solvent formulation. This innovation is aimed at developing such a solvent with added dispersant to solubilize the Asphaltene debris.
3.1. Problem identification:
Since asphaltenes are amorphic "non-crystalline" in nature and do not uniformly melt in the presence of heat the heavy organic deposits resulting from asphaltene flocculation are quite hard to deal with in petroleum production practices. Asphaltenes are also a common nucleation site for paraffin crystallization and are, therefore, often found within the same deposit. Asphaltenes and resins are responsible for adding most of the color to crude oils. Most of the wells of offshore field are facing production decline due to down hole Aphaltene precipitation.
Colloidal Instability index (Cll) is a measure of asphaltene precipitation in depleted reservoirs operating near the bubble point pressure. Cll values over '1' generally indicate possibility of asphaltene precipitation whenever there is change in flow parameters - Pressure, Temperature and Composition.
Cll values of crude indicate:
■ Appreciable asphaltene content in crude
■ Cll >1 In all the areas.
■ Cll is maximum in phase-Ill of field.

■ SIMDIS analysis shows, carbon atom distribution is maximum at C11 and C12. Lighter crudes are prone to asphaltene precipitation than heavier ones.
■ Considering high BHT and low wax content the problem of wax deposition near well bore is negligible.
Asphaltene problem is existing in all the areas of field. Intensity of problem is more in A layer compared to B layer. Solubility of Asphaltene is limited to almost 58% in solvent without dispersant •
3.2 Mitigation methods:
Heavy organics deposition due to Asphaltene floccutation can be controlled through the better knowledge of the mechanisms that cause the deposition in the first place. Processes can be altered to minimize the deposition and chemicals can be used to possibly control the deposition when process alterations are not effective.
Chemical treatment techniques include: Addition of dispersants, and aromatic solvents which may be used to control asphaltene deposition. Dispersants work by surrounding the asphaltene molecules similar to the natural resin materials. Aromatic solvents for asphaltene deposits need to have a high aromaticity to be effective.
In order to investigate about asphaltene solubility or precipitation, the activity of inhibitors is not only dependent on the acidic head, but also of the aliphatic or aromatic tail of the inhibitor.
Solvent treatment of the oil is considered to be beneficial in some cases because it dilutes the crude oil and reduces the tendency of the heavy organics to precipitate. Xylene is generally the most common solvent selected to be used in well stimulations, work overs, and heavy

organics inhibition and cleaning. In some cases Xylene injection through the non-producing string actually may help to minimize the heavy organic deposition problem. In oil fields with frequent need for aromatic wash it may be necessary to design an aromatic solvent with stronger wash power and better economy for the particular deposit in mind. Laboratory tests may be necessary to blend the most appropriate aromatic solvent and / or dispersant for a given oil field from the points of view of effectiveness, economy, and environmental friendliness. Specific formulations may be blended to achieve the goal of preventing or cleaning the heavy organics deposits which can be used by the field engineers.
3.3. Laboratory studies:
Crude oil samples from different locations of field were collected and carried out following analysis:
1. Saturates, Aromatics, Resins, Asphaltens (SARA) analysis.
2. Simulated Distillation Analysis (SIMDIS)
3. Determination of Colloidal Instability Index (CM) values of crude oil.
4. Dispersant efficiency on crude residue solubility.
5. Dispersant efficiency by Core flow studies -rock matrix clean up.
3.3.1. Determination of SARA And Calculation Of Colloidal Instability Index (CI1):
CII is a measure of Asphaltene precipitation in depleted reservoirs operating near the bubble point pressure. CI! values over '1' generally indicate possibility of asphaltene precipitation whenever there is change in flow parameters - Pressure, Temperature and Composition:

Method adopted for Saturates, Aromatics, Resins, and Asphaltenes:
(a) 25 ml of n-Pentane / n-Heptane is added to 2 g of oil, stirred, and allowed to stand for 30 minutes at room temperature. The asphaltenes are then removed by vacuum filtration through a 0.45 urn membrane, and the pentane is recovered by rotary evaporation at 30°C, leaving the maltenes.
b) 0.4 g to 0.5 g of maltenes is placed in an open glass column (400 mm x 19 mm I.D. x 22 mm O.D., fitted with stopcock) packed with 30 g silica, topped with 1.5 cm anhydrous sodium sulphate, and saturated with hexane.
c) The sample is eluted with 100 ml hexaine and 100 ml of eluant is collected and labeled as 'saturates'.
d) The sample is eluted with 100 mL hexane/benzene (1:1) and 100 mL of eluant is collected and labeled as 'aromatics'.
e) The sample is eluted with 100 mL methanol and100 mL of eluant is collected and labeled as 'resins'.
f) The sample is eluted with 100 mL dichloromethane and the eluant is collected and labeled as 'resins'.
g) Rotary evaporation is used to recover the bulk of the solvents, followed by nitrogen blow down.
h) Each hydrocarbon group is weighed after solvent recovery is complete. The weights of the two resin fractions are combined.
Samples are run in duplicate and the mean is as reported in Figure 1.

Cll Calculation:
Cll Values as given in Fig.2 are calculated from the given equation: Cll = Saturates+ Asphaltenes / Aromatics+Resins
From the above table it is evident that the CIl values are very high for Phase - IN (HY-4) compared to other fields. Severe precipitation is expected in Phase-Ill, compared to other areas.
3.3.2 SIMDIS Analysis:
Simulated distillation (SIMDIS) analysis provides an insight to the carbon atom distribution of the crude oil. It helps to identify the nature of crude. SIMDIS analysis is carried out using programmed capillary/ wide bore capillary, gas chromatograph. Carbon atom distribution as a function of boiling point is determined and quantified as given in Fig.3. This analysis helps to identify the optimum length of the alkyl chain of the dispersant for effective Asphaltene clean up.
3.3.3 SELECTION OF SOLVENT AND DISPERSANT:
In oil fields with frequent need for solvent wash it may be necessary to design an aromatic solvent with stronger wash power at minimum cost for particular deposit in mind. Laboratory tests may be necessary to blend the most appropriate aromatic solvent and / or dispersant for a given oil field from the points of view of effectiveness, economy, and environmental friendliness. Then special formulations may be blended to achieve the goal of preventing or cleaning the heavy organic deposits.
Conventional aromatic solvent consists of combination of three components viz. Toluene, Xylene, Naphthalene in a specified ratio.

Doping this solvent mixture with an optimum dose of 'Dispersant' enhances over all clean up capacity of formulation. Tentative percentage of solvent is:
1. Diesel-25%
2. Xylene-40%
3. Toluene-30%
Alkylated Phenolic Ethanoxy Ether is chosen as Asphaltene Dispersant and blended with solvent (1.5-4% wA/) for the optimization studies.
3.3.4 DISPERSANT EVALUATION:
Filtration Method: The efficiency of dispersant is evaluated based on its ability to disperse and keep the Asphaltene in suspended form. Crude oil samples were distilled off, up to a temperature of 280 deg C and the residue is used for evaluating the efficiency.
2 grams of residue obtained from crude distillation is weighed and dissolved in solvent containing selective proportions of Xylene, Toluene, Naphthalene, in diesel. Specific dose of dispersant is added and filtered through micro fine filter paper (No: 41). The quantity of undissolved material retained on the filter paper is weighed • and percentage of dissolution is calculated and the results are set out in Fig Nos.4A and 4B.
Observation: There is no significant change in the solubility of asphaltene with increase in dispersant concentration from 1.5% to 4% (w/v). Dispersant dose of 1.5% is sufficient to achieve over 90% solubility.

3.3.5 DISPERSANT DOPED SOLVENT EFFICIENCY BY CORE FLOW STUDIES:
A representative core sample from the field is collected and plugged to desires dimension (11/2" X 3"). Placed in to a core holder and applied confining pressure 2500psi. Saturated the core with 2 % KCI solution; recorded base line pressure at an injection rate of 3 cc/min with n-Heptane. Injected crude oil- N-Heptane mixture (1:40 ratio), over 4-5 pore volumes to facilitate precipitation of Asphaltene in the pore throats ( it simulates the formation damage of the rock as observed in the field ). Pumping of mixture is stopped when the pressure shoots up to a value close to confining pressure due to sphaltene precipitation. Through this damaged core umped the Solvent (Diesel-Xylene-Toluene-Naphthalene) mixture, with and with out dispersant; recorded pressure profile. Finally reversed the core flow direction and established base line pressure with N-Heptane. There is significant drop in the injection pressure and improvement in the core permeability observed after solvent wash. Plot of injection pressure as a function of time over entire operations indicate that solvent wash with suitable dose of dispersant improves the fluid flow rate significantly. At ambient temperature the rate of dissolution of deposits is slow compared to the rate at 90 deg C. Soaking time, required for removal of organic deposits is less at elevated temperature compared to ambient. At 90 deg C, the dissolution of Asphaltene deposits is fast enough, so, the soaking time required is minimum.
Observation on Core flow studies:
Figure.5A depicts higher injection pressure for the flow of solvent through Asphaltene precipitated core without dispersant dosing. Figure.5B shows reduced pressure for the flow of solvent with added

dispersant dose (1.5% w/v). At higher temperature the resistance for the flow is reduced drastically indicating clean up of the precipitated Asphaltenes as shown in Figure 5C.
Over all observation on Innovation:
■ Asphaltene problem is exists in all the areas of offshore field.
■ Crude is rich in lighter hydrocarbons as is evident from SIMDIS analysis. C11, C12 is major constituent. Such crudes are prone to asphaltene precipitation.
■ Solubility of Asphaltene is limited at almost 58% in solvent without dispersant.
■ Dispersant in the formulation improves the solubility and helps to keep asphaltene in suspension.
■ Alky! phenol polyethanoxy ether is most suitable option as dispersant to achieve over 90% solubility.
■ Core flow studies show considerable improvement in damage removal with solvent containing 1.5% dispersant.
■ Minimum soaking time is required for solvent above at 90 deg C, for asphaltene clean up.
4.0 FIELD APPLICABILITY:
The innovated formulation is applied in the field for removal of down hole Asphaltene precipitates. Initially over five wells were identified and prepared detailed job design for execution. Field job is carried out in the following: sequence.
■ Measure injectivity of the well before attempting solvent job.
■ Preflush with diesel + 5% EGMBE
■ Squeeze the solvent in near wellbore area with the following formulation:

Solvent formulation: Diesel- 25% + Xylene- 40% + toluene- 30% + 10 % (wt/v) naphthalene + 1.5% dispersant ■After flush with diesel +5% EGMBE ■Flow back the well
The actual field test data reported for each well is as set out in Fig.6.
5. SUMMARY OF THE INVENTION:
Down hole Asphaltene clean up is a necessity for enhancing and sustaining oi! production. Conventionally solvent wash is recommended for Asphaltene removal; this innovation improves many folds the solvent power on incorporating a 'Asphaltene Dispersant'. Invented solvent formulation is effective up to 120 deg C with increased sustainability of oil production. Alkyl phenol polyethanoxy ether, at an optimum dose of 1.5% of is recommended as dispersant to achieve over 90% Asphaltene solubility. The formulation has following composition:
Diesel- 25% + Xylene - 40% + toluene- 30% + 10 % (wt/v) naphthalene + 1.5% dispersant (Alkylated phenolic polyethanoxy
ether)

BRIEF DESCRIPTION OF DRAWINGS
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
1) Fig-1 is a table showing the results of SARA analysis on four different samples of offshore field.
2) Fig -2 is a table showing results of CM calculations analysis on four different samples of offshore field.
3) Fig.3 is a table showing results of SllvlDIS analysis crude oil sample.
4} Fig,.4A. Is a table showing results of Dispersant doped, solvent efficiency on crude oil residue with different dispersant molecules.
5) Fig.4B is a table showing results of Dispersant doped solvent efficiency on crude oil residue with Alkylated phenolic ether.
6) Fig.5A is a diagram of pressure profile solvent flow through core as a function of time without dispersant at ambient temperature.
7) Fig 5B is a diagram of pressure profile of Solvent flow with dispersant at ambient temperature.
8) Fig 5C is a diagram of pressure profile of solvent with dispersant at 90 Deg Celsius.
9) Fig.6 is a table showing oil gain on field application of innovated solvent.

We claim:
1. Chemical formulation of the solvent consisting of 25% Diesel, 40% Xylene, 30% toluene, 10 % Naphthalene (wt/v) with 1.5% dispersant (Alkylated phenolic polyethanoxy ether) is effective in dissolving Asphaltene precipitates.
2. Asphaltene dissolution rate is faster at temperatures higher than 90 degree celsius with reduced soaking time.
3. A higher dose of the dispersant in the range of 2.0 % is required for Asphaltene dissolution at temperatures lower than 90 degree Celsius.