RU2609031C1 - Composition of ion-modified water for increasing reservoir recovery - Google Patents

Abstract

FIELD: oil industry.

SUBSTANCE: invention relates to oil industry, in particular to compositions for increasing reservoir recovery, laid with carbonate reservoirs with hydrophobic or with mixed wetting ability. Composition provides higher oil recovery factor due to increase in efficiency of oil displacement and larger coverage of reservoir at flooding of carbonate deposits with hydrophobic or mixed wetting ability. Present invention comprises preparation of ion-modified water with a specific detailed ion composition, ensuring maximum change in rock wettability towards hydrophilization, that eventually leads to extraction of additional oil due to increase in displacement and coverage factors. Composition of ion-modified water for increasing reservoir recovery includes hydrocarbonate, sulphate, chlorine, calcium, magnesium, sodium, potassium ions. Disclosed composition of ion-modified water has following advantages: simple and easy to manufacture (slightly differs from reservoir-pressure maintenance with water of arbitrary composition), considerably cheaper surfactant, provides considerable increase in K_vyt and change in wettability.

EFFECT: use of present composition enables to mobilise and displace additional oil volume and increase oil recovery factor.

1 cl, 4 tbl, 3 dwg

Description

The invention relates to the oil industry, in particular to compositions for increasing oil recovery, folded by carbonate reservoirs, hydrophobic or with mixed wettability.

It is known to use slightly saline water in carbonate reservoirs. The modification of the chemical composition of the injected water provided an improvement in the wettability of the surface of carbonate rocks. The results of experiments on spontaneous impregnation on samples taken from oil-bearing zones and exposures of various carbonate formations are presented. In experiments on spontaneous absorption, enhanced oil recovery ranged from 4 to 20% of the initial reserves, which indicates a variety of reactions and the complexity of the mechanisms of exposure. According to studies, the injection of weakly mineralized water into carbonate formations seems promising for increasing oil recovery. [Low Salinity EOR in Carbonates / J. Romanuka [et al.] // 18 SPE IOR Symp. (Apr 14-18, 2012; Tulsa, Oklahoma). - 2012. - SPE 153869.]

The disadvantage of this work is the lack of a fundamental physical or chemical description of the processes and the detailed composition and properties of the water used and, as a consequence, the need for additional studies to better understand the mechanisms.

Compositions with controlled salt composition are also known that are used in water flooding to increase oil recovery from terrigenous and carbonate formations, the reaction mechanisms of which are not the same due to differences in the mineral composition of the rocks and formation characteristics. It is assumed that ions in the altered water change the surface electric potential of carbonates, making it negative, and thus enhance the repulsion of oil (negatively charged). As a result, the wettability of the rock changes, which becomes more hydrophilic. The authors of the article conducted a study of the surface potential of oil and limestone particles at a temperature of 50 ° C. Change in ionic strength is possible by using formation water (salt content 230,000 ppm), sea water (54,000 ppm), water from shallow aquifers (5000 ppm) and fresh water. At pH 8, two-phase (oil in water, limestone particles in water) and three-phase (oil and limestone particles in water) systems were studied. It was found that the largest change in the surface potential of oil droplets was observed upon exposure to 10% diluted seawater, seawater not containing doubly charged ions (Ca ²⁺ and Mg ²⁺ ), and deionized water as a result of adsorption of OH ^-1 ions at the interface oil-water. Sodium sulfate solutions (7120 ppm) also increased the absolute value of the potential of oil droplets. The effect of ionic strength on the potential is more significant for hydrophobic particles of limestone than for samples with intermediate wettability. [Alotaibi, M.V. Electrokinetics of Limestone Particles and Crude-Oil Droplets in Saline Solutions / MB Alotaibi, HA Nasr-El-Din // SPE Reservoir Evaluation & Engineering. - 2011, Oct. - Vol. 14, N5. - P. 604-611.]

The disadvantage of this work is the use of only sea water or its modifications and the incomplete knowledge of the interaction between injected water, reservoir oil and limestone particles, as well as the lack of an accurate ionic composition of low-saline water.

Closest to the proposed invention in technical essence is a composition for increasing oil production and final oil recovery from carbonate formations with controlled salinity of the injected water and its ion content. Analyzing the research results, the authors note the possibility of a significant increase in oil production from carbonates during the injection of a saline solution with optimized ionic composition. It was also established that the main mechanism for increasing oil recovery is the change in wettability. The article presents the results of new laboratory studies on cores taken from different carbonate formations to study the effect of ionic composition on oil recovery in the process of injecting modified water. The results of the first field experiment in a carbonate reservoir, which showed the potential for the injection of “smart water”, are presented. Prepare "smart water" (Smart Water) by diluting seawater with fresh water, proportionally changing its ionic composition. A significant increase in oil recovery was observed when diluting sea water in 2 times and 10 times. [Improved / Enhanced Oil Recovery from Carbonate Reservoirs by Tuning Injection Water Salinity and Ionic Content / A .. Yousef, S. Al-Saleh, M. Al-Jawfi // 18 SPE IOR Symp. (Apr 14-18, 2012; Tulsa, Oklahoma). - 2012. - SPE 154076. - 18 p.]

The disadvantage of this work is the use of exclusively sea water and its modifications, a proportional change in the ionic composition (and not individual for each component), and the lack of an indication of the exact ionic composition of the injected solution.

The objective of the invention is to increase the oil recovery coefficient by increasing the efficiency of oil displacement and increasing the coverage of the formation by exposure during flooding of carbonate deposits with hydrophobic or mixed wettability. The invention also solves the problem of creating ion-modified water with a specific detailed ionic composition, which provides the maximum change in the wettability of the rock towards hydrophilization, which ultimately leads to the extraction of additional oil due to an increase in the displacement and coverage coefficients.

The tasks are solved due to the fact that the composition of ion-modified water to increase oil recovery according to the invention includes ions of bicarbonate, sulfate, chlorine, calcium, magnesium, sodium, potassium in the following ratio of components:

The essential features of the proposed composition are:

1. Ionic modification of the composition.

2. The list of components.

3. The quantitative ratio of the components.

Sign 1 is common with the prototype, signs 2-3 are significant distinguishing features.

SUMMARY OF THE INVENTION

The desired ionic component composition is obtained by dissolving in fresh water a predetermined amount of the following salts:

Water is preliminarily purified from mechanical impurities, biologically active objects, and chemically active substances. Salts are pre-crushed with a special grinder to the size of the main phase of not more than 1 mm. After that, using a metering device, the calculated amount of salts is dissolved in water by stirring with a mechanical stirrer. Table 1 shows examples of the proposed ion-modified water in the claimed intervals of the composition.

The invention is also illustrated by the following figures and table:

Table 2 - The results of cyclic filtration of formation and ion-modified waters;

FIG. 1 - Coefficients of oil displacement by various agents (produced water, ion-modified water, surfactants) during spontaneous capillary impregnation;

FIG. 2 - Phase permeability during forced displacement by formation water and ion-modified water (cyclically);

FIG. 3 - Change in pressure drop for different types of water and their mixtures (determination of compatibility).

The implementation of the invention.

The selection of the composition for the conditions of a particular field is carried out by conducting a series of laboratory studies carried out in a certain order:

- At the first stage, the mineralogical and elemental composition of the rock, the component ionic composition of formation water, the component composition of oil and the content of active substances (acids) in it are determined.

- Determine the wettability of the rock, its type and source (in the case of hydrophobicity).

- Determine the reaction activity of the rock surface during the injection of water of various ionic composition with a control determination using distilled water.

- After this, the initial capillary forces are determined (before exposure).

- Select the composition of ion-modified water, providing maximum reactivity with the surface of the rock.

- Determine the change in capillary forces (after exposure) and wettability.

- For research use core material, oil and produced water of a particular field. The core is subjected to extraction with agents that do not change its wettability in order to maintain the initial state. Then the core samples are saturated with oil and kept in oil in order to guarantee the restoration of reservoir properties in terms of wettability.

- After that, the compatibility of ion-modified and formation water is determined.

The optimal composition of ion-modified water is checked in an experiment on spontaneous capillary impregnation and in an experiment on forced displacement of oil by formation and ion-modified water.

Determine the coefficients of oil pre-displacement by ion-modified water during impregnation and displacement, reaction time, phase permeability during displacement, change in permeability for various waters (formation and ion-modified) and their mixtures.

In this case, core samples are taken from various parts of the reservoir in order to evaluate the effect for rocks with different wettability.

Example

2 core samples are taken: mainly hydrophobic and with mixed wettability. Samples are placed on capillary impregnation in formation water. The limiting coefficients of oil displacement ( _Kout ) are determined for produced water after stabilization of the value of _Kout . Then, the water impregnating the samples is replaced with ion-modified. After a certain exposure time required for the reaction, an additional volume of oil is displaced. Determined limit for the ion-modified water To _stretch (after stabilization values) that make up 0.305 and 0.505, respectively (the gain K with respect to _draw produced water 0.19 and 0.215, respectively).

To monitor the received values and to determine the maximum capacity of the wettability changing washed PAVom samples, determined as a result of limiting _drawing K. An example is shown in FIG. 1. According to this example, the maximum achievable _Kout are 0.65 and 0.83, respectively. Thus the use of ion-modified water can achieve _draw K 0.305 0.65 from potentially possible (~ 47% capacity) to a hydrophobic manifold and K 0.505 _drawing of potentially possible 0.83 (~ 61% capacity) for the collector with a mixed wettability.

Then, the phase permeabilities are determined on the samples during a cyclic change in the exposure agent (formation water / ion-modified water). An example is shown in FIG. 2. An example of the cycles used in the experiment is shown in Table 2. From FIG. 2 and Table 2 shows that the phase permeability for ion-modified water (points 4 and 6) is significantly less than for produced water (points 3, 5 and 7). This means that ion-modified water reacts with the rock (and the oil film) and when it moves along the surface, additional resistance arises (due to electrochemical interaction), and also mobilizes previously immovable oil (due to changes in the wettability and “sticking” of the oil from the surface of the rock). Formation water does not enter into a reaction, therefore, its phase permeability is higher than that of ion-modified water. The appearance of an additional volume of mobile oil when exposed to ion-modified water leads to a decrease in phase permeability to water and, accordingly, an increase in phase permeability to oil. The value of phase permeability for the first injection cycle of ion-modified water (point 4) is less than for the second cycle. This is due to the fact that the effect on the first cycle is greater (an effect is exerted on a larger surface area and a larger volume of oil is mobilized) than on the second and subsequent ones (ultimately the entire effect can be obtained already on the first cycle). Accordingly, the greater the difference between the volumes of mobilized oil at different stages, the greater the difference between the phase permeabilities in water. A similar situation is observed for phase permeabilities for formation water (points 3, 5 and 7). In general, the phase permeability in water will increase with each subsequent treatment due to the fact that the volume of oil recovered as a result of processing will be replaced by water (oil saturation decreases, water saturation increases). Thus, an increase in phase permeability in produced water during sequential treatments means the extraction of an additional volume of oil.

This example shows that:

- ion-modified water reacts on both treatment cycles (points 4 and 6),

- the effect of the first treatment with ion-modified water is higher than that of the second, which can be seen both in the difference in phase permeability between points 4 and 6, and in that the phase permeability in produced water before and after (points 5 and 7) of the second cycle treatments with ion-modified water (point 6) differ slightly (within the margin of error), which means that water saturation (oil saturation) has changed slightly. This, in turn, means that a significant amount of previously immovable oil was not mobilized, which means that almost the entire effect from the point of view of increasing _Kout was obtained in the first treatment cycle.

Then, on the composite core sample, the pressure drop (hydraulic resistance) is determined during the injection of various waters and their mixing. In the case of significant incompatibility of the formation and ion-modified waters (salt precipitation into a solid sediment), a significant decrease in permeability and an increase in pressure drop occur.

With minor or short-term significant changes in water can be considered fundamentally compatible. An example of such a definition is presented in FIG. 3. A composite extracted core sample (including all types of void space — pore, fractured, cavernous, mixed, found in the reservoir in the entire range of permeabilities for maximum representativeness) is saturated with formation water. Ion-modified water is pumped into the sample (100% water-saturated, without oil). In this case, the pressure drop is measured (the reciprocal of the permeability). As can be seen from FIG. 3. Short-term increases in pressure drop occurred (during injection of 0.1, 0.23, 0.7 pore volume) due to precipitation. However, this precipitate subsequently dissolved and had an insignificant short-term effect. Thus, they conclude that the water is in principle compatible.

Thus, the proposed composition of ion-modified water can be effectively used to displace oil during flooding of carbonate deposits with hydrophobic or mixed wettability and has the following advantages: it is simple and technologically advanced to manufacture (it differs slightly from PPD with water of arbitrary composition), it is significantly cheaper than surfactant, it allows to obtain a significant increase in _Kout and a change in wettability. Thus, the use of this composition allows you to mobilize and displace additional oil and increase oil recovery factor.

Claims (2)

The composition of ion-modified water to increase oil recovery, characterized in that it includes bicarbonate, sulfate, chlorine, calcium, magnesium, sodium, potassium ions in the following ratio, mg / l: Hydrocarbonates (HCO ₃ ^- ) 110-130 Sulphates (SO ₄ ^2- ) 9100-9300 Chlorine (Cl ^- ) 4300-4500 Calcium (Ca ²⁺ ) 450-550 Magnesium (Mg ²⁺ ) 1050-1100 Sodium (Na ⁺ ) 4500-5000 Potassium (K ⁺ ) 350-420

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