RU2425967C1 - Reservoir recovery improvement method - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: in reservoir recovery improvement method involving pumping to formations of the compound containing clay and metal salt solution the thin clay solution with additive of magnesium sulphate is used as the above compound.

EFFECT: higher control efficiency of permeability of oil deposit, which allows to increase oil recovery factor.

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Description

The invention relates to the oil industry and may find application in the development of oil deposits at a late stage, providing increased oil recovery.

There is a known method of developing an oil reservoir, in which oil is extracted through production wells, the working agent is injected through injection wells and periodically injected water dispersion through the injection well. In an aqueous dispersion, a mixture of clay powder and a water-soluble polymer powder is used as the dispersion phase [1].

The disadvantage of this method is the low efficiency, especially at a late stage of development, because in a porous medium, aqueous solutions of the components practically do not mix and the injected water rims of the polymer and clay work without the formation of associates, which does not create effective resistance to the flow of water during subsequent flooding. As a result, oil recovery remains low.

During the development of heterogeneous permeability oil reservoirs to increase oil recovery, a working agent and a polymer suspension are pumped through injection wells. Oil is taken through production wells. After a time period of the planned decrease in oil production, rarefaction is performed in the area of the injection well and pumping of a suspension with a particle size of from 0.001 to 1.0 μm of a polymer containing from 1 to 80% of the gel fraction. In this case, the injection changes stepwise by 10-70% [2]. The disadvantage of this method is the high cost of materials and work, low oil recovery.

Another method relates, in particular, to methods for developing an oil reservoir represented by heterogeneous formations with conducting insulating work to even out the injectivity profile of injection wells and to limit water inflow to production wells. This method of developing an oil deposit involves injecting into the formation an aqueous solution of sodium silicate and a structure-forming reagent, a zeolite-containing rock pretreated with sulfuric or hydrochloric acids, and additionally carry out exposure. Moreover, the indicated solution of sodium silicate and zeolite-containing rock is pumped simultaneously or sequentially. The technical result is to increase the efficiency of the development of oil deposits and its oil recovery [3].

A known method of regulating the permeability of a heterogeneous formation by sequentially injecting into the formation through an oil well rims of oil, a gel-forming solution containing aluminosilicates, hydrochloric acid and water; after the gel-forming solution, the rim of the solvent is pumped [4]. EFFECT: increased production of stocks of water-flooded oil reservoirs with zonal heterogeneity of permeability due to more complete coverage by oil displacement from stagnant weakly drained reservoir zones by pumping highly effective chemical compositions with selective effects into production wells. The invention relates to the oil and gas industry, in particular to methods of displacing residual oil from heterogeneous permeability formations by plugging a flooded reservoir with a highly effective composition of chemicals.

Due to the depletion of many oil fields and the need for their rehabilitation, there is a sharp increase in interest in nanotechnology, which makes it possible to manage the balanced development of oil deposits and sharply increase the oil recovery coefficient [5, 6].

The closest analogue to the proposed invention is a method of increasing oil recovery, including the injection into the formation of a composition containing clay and a solution of metal salts [7].

The disadvantage of this method, which we selected as a prototype for the majority of coinciding features, is the underestimation of the effect on the oil recovery of changes in the porosity of the formation under the action of salts of certain chemical elements, for example magnesium.

Oil and gas are found in a variety of natural reservoirs, including limestones and dolomites. Such rocks contain 40% of the world's oil reserves. Dolomitization leads to an increase in pore volume in dense limestones due to changes in the size and topology of the void space. In Western Siberia, in many Paleozoic reservoirs, oil deposits were found precisely in dolomitic limestones.

The objective of the invention is to significantly increase the efficiency of regulation of the permeability of oil deposits, which allows to increase the oil recovery ratio.

To solve this problem, it is proposed to initiate an accelerated technogenic process of metasomatic dolomitization and create highly productive foci in oil fields by injecting magnesium-containing fluid into the formation.

The technical essence of the invention lies in the fact that in the known method of increasing oil recovery, including the injection into the formation of a composition containing clay and a solution of a metal salt, a small-clay solution with the addition of magnesium sulfate is used as the specified composition.

The introduction of a composition containing an aqueous solution of magnesium sulfate, including magnesium nanoparticles, provides the induction of metasomatic dolomitization of pores with the replacement of calcium ions in the rock by magnesium ions.

The essence of metasomatic dolomitization is as follows:

the radius of the calcium ion (cation) (Ca ²⁺ ) is 0.99 Å or 99 nm, and the magnesium ion (cation) (Mg ²⁺ ) is 0.66 Å or 66 nm. In the process of replacing calcium with magnesium, a significant void space is formed. Thus, nanosized metasomatic processes in carbonate rocks contribute to the formation of good high-yield reservoirs.

Metasomatism is a reaction of adaptation of a rock to a change in the physical and chemical conditions of its condition. As a rule, metasomatic processes occur in the mode of reactions between the solid (rock) and liquid or gaseous (fluid) phases while the rock remains in a solid state. They lead to a change in the chemical composition of the rock by replacing some minerals with others under the influence of a mobile, chemically active heat and mass carrier in a gradient thermodynamic field. These processes are essentially nonequilibrium.

Successful use of the proposed nanotechnology can have a significant impact on the duration of field development and ultimate oil recovery.

With dolomitization, not only porosity increases, but also permeability. For example, in Canada, permeability in limestone reservoirs is 6 · 10 ^-3 μm ² , and in dolomitic reservoirs it is 8 · 10 ^-3 μm ² .

Dolomites are primary-sedimentary and secondary-epigenetic. Secondary dolomitization is always accompanied by cracking, which can provide high rock permeability. The newer the cracks, the wider they are and the higher their permeability. Crystals in limestones have a pronounced tendency to orient their axes parallel to the bedding planes. In the Dolomites, the crystals are oriented quite randomly.

Differing from limestones in a significantly larger volume of intercrystalline pore space, dolomites have a correspondingly larger surface for the interaction of the mineral part with the fluids circulating in them.

As a rule, substitutional dolomites form fractured cavernous reservoirs, which are characterized by newly formed secondary porosity and cavernosity (Fig. 1 - core of dolomite substitution with caverns; Fig. 2 - thin section (in transmitted light).

In 2009, at the Maloichsky field in the Novosibirsk region (Fig. 3. The Maloichsky field. Novosibirsk region (taking into account the results of 3D seismic exploration):

1 - surface isohypses of carbonate Paleozoic rocks, m;

2 - subvertical zones of erosion-tectonic protrusions;

3 - alleged deep faults;

4 - tectonic disturbances;

5 - foci of secondary dolomitization;

6 - wells that gave an influx of oil;

lithofacies 7 - organogenic reefs; 8 - advanced loop; 9 - zarifovogo lagoon.

well No. 117 was drilled, in which a fountain oil flow with a flow rate of 280 tons / day was obtained from Devonian dolomitic limestones. Focal dolomitization is clearly indicated at the Maloichsky field, which ultimately determines the productivity of the wells. The foci in the western and southwestern parts of the field (SLE: 4, 9, 117, 6, 2) are characterized by active secondary dolomitization along the Middle Devonian reef. Areas with highly productive wells are clearly confined to the facies-tectonic zone (Fig. 2).

Interestingly, a change in the reservoir properties of carbonate rocks is reflected in a change in the carbon isotopic composition of the carbonate rocks themselves, and especially CO ₂ , which allows them to be used as additional criteria for the predictive assessment of reservoirs. Based on detailed isotope studies, it was found that in Western Siberia, the main source of CO ₂ are Paleozoic carbonate rocks, although some researchers consider it to be deep.

A study of the material composition and reservoir properties of the Paleozoic carbonate rocks of the Maloichsky area made it possible to distinguish within its limits separate zones, each of which has a specific isotopic composition of carbon CO ₂ and carbonates. The distinguished zones differ in δ ¹³ С values of carbonate rocks, which in one zone are 0.5–0.8%, and in the other 1.3–3.7%. These differences in the carbon isotopic composition of carbonate rocks in different zones of the considered area reflect the degree of their post-sedimentation transformation.

These processes can occur as a result of migration of CO ₂ in the composition of hydrothermal solutions. As can be seen, secondary dolomitization is of greatest importance in the processes under consideration. Essentially, it is a metasomatism that occurs by replacing a calcium ion with a magnesium ion.

There are a number of conditions conducive to active metasomatic processes. Particularly important is the recharge of CO ₂ . This natural phenomenon is widespread enough.

It is known that in sedimentary and magmatic complexes, a wide development of metasomatic processes is observed, which to some extent transform primary rocks and have a significant impact on their mineral specialization.

The question arises - is it possible to initiate an accelerated technogenic process of metasomatic dolomitization and create or maintain highly productive foci in the field. In fact, this will allow to manage the process of field development and increase the oil recovery coefficient. For this, it is necessary to establish the carbonate content of the prospective horizons, determine the composition of the carbonate material and formation water, and then implement the technology of injecting magnesium-containing fluid into the formation, i.e. magnesium in the size of nanoparticles. In particular, metasomatic dolomitization can be effectively stimulated by pumping an aqueous solution of magnesium sulfate MgSO ₄ into the formation. As a result, there is an increase in the specific surface of the void space, various thermodynamic gradients and the formation system change (at least within a certain focus), and they are stimulated to activate many processes (formation of fracturing, flow of fluid mass from the block matrix into cracks and even the formation of hydrocarbon masses). To a large extent, percolation processes are activated, production rates, well productivity and oil recovery increase. In some cases, the process of forced and accelerated dolomitization (metasomatism) can be accompanied by wave and thermal effects. Of course, these technological operations are classified as sparing, in fact, we accelerate or regulate natural processes.

The development of this technology within the field at the Maloichskoye oil field, where industrial oil content in dolomitized limestones of the Middle Devonian due to the substrate of carbonate reef massifs is established, opens the way to intensive development of the Paleozoic in Western Siberia and ancient carbonate massifs of Eastern Siberia. At the same time, it can be used for terrigenous rocks with a high content of carbonate cement in the rocks. Increased carbonate content and high CO ₂ content are often observed in the Jurassic and Cretaceous rocks of Western Siberia. Dolomitization is often carried out by microgranular and pelitomorphic calcite cement, foraminifer shells, algal residues, and various organogenic detritus. In metasomatic dolomites, pores 0.2-0.8 mm in size and caverns larger than 1 mm are often formed. Low-clay solutions can be used in various compositions with clay contents from 1 to 12 wt.%, The amount of dissolved magnesium sulfate is also assigned depending on the material composition and reservoir properties of the carbonate rocks of the treated formations.

Example 1

Table 1 shows the actual data on the treatment of the bottom-hole formation zone by small-clay solutions with magnesium sulfate additives at OJSC “Surgutneftegas”.

Table 1 Enterprise: NGDU "BISTRINSKNEFT"
Deposit: 206 Bystrinskoye Well number 5 1 Additional oil production, t The increase in oil flow rate, t / s Oil production rate (throttle response), t / s To GTM After 3141 BS18-20 19 0.1 1,6 3,1 4016 BS16-17 6203 20.3 183.6 322,4 6179 AC7 94 0.4 1.3 2.2 1406 US2 2400 6.8 2.5 3.4 254 BS2 2898 8.7 309.7 233.8 337 BS2 1863 5.1 201.9 294.2 741 BS18-20 eighteen 0.1 5.7 6.7 1224 AC8 322 2.7 57.8 123.5 2021 US2 19 0.1 3,5 4.8 2220 US2 70 0.6 0.6 0.9 2229 US2 1959 6.4 1,5 8.4 2230 US2 5 0 2.9 2.7 2238 US2 473 1.9 93.9 125.1 2262 US2 5075 42.3 19,4 35,4 2277 BS16-17 168 1.7 1,1 2,3 2308 US2 48 0.8 38.1 72 3007 BS18-20 465 6.9 167.5 203.9 3026 BS18-20 307 2 201.6 218.1 3049 BS18-20 four 0 447.1 338.4 3073 BS18-20 1592 10.5 31.9 36.1 3115 BS16-17 325 3.6 0.3 3.4 3129 BS 18-20 2978 eighteen 186.6 200.5

Recipe for a clay solution:

1. PBMA - bentonite clay powder - 10%

2. KMTS-600 - carboxymethyl cellulose - 10%

3. Hypane-hydrolyzed polyacrylonitrile - 5%

4. USR - carbon-alkaline reagent - 8%

5. Water - the rest (68%)

To this small clay solution was added a 10% aqueous solution of magnesium sulfate. Depending on the degree of dolomitization of the reservoir, the following results are obtained by the proposed method:

1) the dolomitization coefficient is 16.7%, the volume of the magnesium sulfate solution is 58%, the porosity is up to 18%, after it is 33%, the permeability is 0.16 and 0.31 μm ^2, respectively;

2) dolomitization coefficient of 15.4%, the volume of magnesium sulfate solution is 50%, porosity is up to 12%, after 24%, permeability is 0.14 and 0.22 μm ^2, respectively.

The successful use of the proposed method for regulating the permeability of the oil reservoir and the corresponding nanotechnology significantly increases the duration of field development and final oil recovery.

Information sources

1. Muslimov R.Kh., Takhautdinov Sh.F., Khisamov R.S. et al. A method for developing an oil reservoir. RF patent No. 2136872, 09/10/1999.

2. Muslimov R.Kh., Khisamov RS, Yakovlev S.A. et al. A method for developing an oil reservoir. RF patent No. 2148155, 10.26.1999.

3. Takhautdinov Sh.F., Gatiyatullin N.S., Bareev N.A. et al. A method for developing an oil reservoir. RF patent No. 2157451, 08/12/1998.

4. Yakimenko G.Kh., Lukyanov Yu.V., Gafurov O.G. and others. A method for controlling the permeability of a heterogeneous formation. RF patent No. 2182654, 02.11.2000.

5. Zapivalov NP, Smirnov G.I., Kharitonov V.I. Fractals and nanostructures in oil and gas geology and geophysics. Novosibirsk: Academic Publishing House "Geo", 2009. - 131 S.

6. Zapivalov N.P., Smirnov G.I. On the fractal structure of oil and gas fields. Reports of the Russian Academy of Sciences, 1995, T.341, N1, C.110-112.

7. Lukyanov Yu.V., Abyzbaev II, Ramazanova A.A. et al. - A method for regulating the development of a heterogeneous oil reservoir. RF patent No. 2249099, 03/27/2005 (prototype).

Claims (1)

A method of increasing oil recovery, including the injection into the reservoir of a composition containing clay and a solution of a metal salt, characterized in that the composition used is a low clay solution with the addition of magnesium sulfate.

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