RU2065934C1 - Method of developing an oil pool characterized by nonuniformity in respect to permeability and oil saturation - Google Patents

Abstract

FIELD: oil and gas production. SUBSTANCE: method consists in pumping in a reagent composition into the stratum through injection wells and withdrawal of oil from productive wells. Composition makeup is selected on condition of developing in drained part of stratum a lower dielectric constant than that in nondrained part, whereas volume of composition prevents its aggressive constituents from reaching the hole bottom. In conditions of West Siberia, employment of high- concentration hydrogen chloride is effective. EFFECT: increased oil production of bed and reduced association water withdrawal. 2 cl

Description

 The invention relates to the development of heterogeneous (in the context of) permeability and oil saturation of the reservoir and can be used in the oil and gas industry.

 The reservoir can be heterogeneous in terms of permeability and oil saturation due to both objective (the process of its formation is not completed) and subjective (distribution of oil saturation in the reservoir after or during its development using the waterflooding method).

A known method of developing oil fields by pumping water into injection wells and the selection of oil and water from producing wells [1]
The disadvantage of this method when it is used in reservoirs that are heterogeneous in permeability and oil saturation is low efficiency due to ballast slippage of water along relatively highly permeable and weakly saturated with oil layers, which leads to an extremely low oil recovery coefficient and the selection of a large amount of associated water from produced ton oil.

Closest to the invention is a development method in which, in order to increase the efficiency of oil displacement, rims of various physicochemical substances are pumped from injection wells: acids, alkalis, polymers, surfactants, carbon dioxide, various kinds of solvents, etc. [2]
The volumes of the rims, as a rule, do not exceed several tens of tons (m ³ , which allows them to cover only the bottom-hole zone of the formation. The fringes or their compositions are intended, as a rule, to increase the coefficient of productivity of the well, to isolate the flooded interlayers, to connect inoperative layers (interlayers) ), alignment of inflow and return profiles.

 The disadvantage of the method adopted for the prototype, when it is used in a reservoir that is heterogeneous in permeability and oil saturation, is low efficiency, either due to the more effective displacement of only the bottom-hole zone of the formation (the bulk of the reserves are not affected), or because of the predominant effect on the drained formation volumes (non-drained parts of the impact do not experience).

 Natural geological and physical factors accompanying the processes of formation and development of hydrocarbon deposits lead to polarization of the skeleton of the reservoir. The latter has its own in-situ electrostatic field and it is in it that the formation fluid is filtered. The cause of the forces acting on the medium in an electrostatic field is its polarization, i.e. the formation of elementary molecular dipoles under the influence of an electrostatic field. In this case, a medium with a higher dielectric constant under the action of electrostatic forces is drawn into the pore space, displacing a medium with a lower dielectric constant.

 The objective of the invention is to increase the efficiency of oil recovery from the bowels by involving in the filtration, with the development system used, non-drained reserves by creating a difference in the permittivity of the filtered and stationary fluids.

 The proposed technical solution involves the development of reservoirs heterogeneous in permeability and oil saturation by injecting a composition of physicochemical substances into the formation through an injection well and taking oil from the production well. The proposed solution differs from the known one in that the composition is selected from the condition of creating a lower dielectric constant in the drained part of the formation compared to the non-drained part and in a volume that excludes the entry of aggressive components of the composition to the bottom of the producing well.

 Replacing the filtered fresh water in the drained part of the formation with a liquid with a low dielectric constant, it is possible to obtain a lower dielectric constant in this volume than in the non-draining part of the formation. Thus, the fixed oil reserves from the latter will flow into the drained volumes of the reservoir, which will lead to an increase in oil recovery and a decrease in the water cut in the production of production wells.

 Under real reservoir conditions, acids with the lowest dielectric constant are most often acid, as applied to the conditions of Western Siberia, in particular, concentrated hydrochloric acid.

Laboratory studies have been carried out to clarify the effect of acids and additives to it of various chemicals on the amount of oil displacement from fixed volumes of the reservoir. The studies were conducted on core samples of the BS ₁₀ formation of the Mamontovskoye field in Western Siberia. Before the experiment, core samples (3x2 cm cylinders) were carefully extracted until the oil was completely washed out of them. Then, residual water was created in the samples by centrifugation with a salinity of 20 g / L, then the samples were saturated under vacuum with an oil model (oil solution in kerosene). Prepared samples were placed in special boxes filled with the studied solutions. The amount of oil displaced was determined daily for 12 days. According to the research results, it was found: with an initial oil content of 75, its final content with capillary displacement with fresh water was 50 with capillary displacement with 24th hydrochloric acid 37
The volume of liquid with a low dielectric constant V _s in the injected composition is determined from the condition
V _pz <V _s << V _before
where V _{pz the} volume of reagents during normal operations with a bottomhole formation zone (up to several tens of m ³ (m));
V _before injection volume limit above which the aggressive agent, in particular hydrochloric acid, can reach the bottom of the production well and to have negative consequences in terms of corrosion columns, downhole and surface equipment. The value of V _pre depends on the heterogeneity of the formation in terms of permeability (the higher it is, the lower the V _pre ), the expenditure of the reagent for the reaction with the skeleton of the formation and reservoir fluids (the higher it is, the greater the V _pre ). For typical conditions, V _pre can be taken at the level of 0.1 0.15 pore oil-saturated volume of the reservoir. Given the economic, technical and technological factors usually take V _pre = 200-400 m ³ .

 Implement the proposed method as follows.

 Based on the results of laboratory tests, the optimal composition is determined. The rim volume can be selected on the basis of technical and economic calculations using the results of actual well operation during the pilot injection of reagents (according to data on additional oil produced per ton of injected reagents).

 The rim is pumped into the injection well by both stationary (pumps of a cluster pumping station) and mobile (CA-320) technical equipment available in the oil industry. Wells for injection are selected according to the results of the analysis of the development of the reservoir.

As an example of the implementation of the proposed technical solution, the experimental injection of acid compositions into the BS ₁₁ layer of the Karamovsky field in Western Siberia is considered. Well 156 was chosen for injection. Production wells 143, 145, 154, 155, 436, 437 surround it. The main geological and physical parameters of the formation in the experimental section: effective oil saturated thickness of 8.4 m; permeability coefficient 0.065 μm ² , porosity 18 of the initial oil saturation 59 water cut of production wells at the beginning of the experiment 85 Injection into well 156 was carried out in October 1990. Under a pressure of 5 12 MPa, CA-320 aggregate was injected with 20 m ^{3 of} mud acid of a concentration of 32,250 m ^{3 of} hydrochloric acid of a concentration of 24 together with a surfactant СНО-3Б of a concentration of 2 and 6 t of a surfactant СНО-3Б of a concentration of 7
09/01/1991, an effect in the amount of 18 thousand tons of additional oil was obtained, of which, due to increased oil recovery, 12 thousand tons Associated water withdrawal reduced by 7.4 thousand m ³ .

Claims (2)

 1. A method of developing a reservoir non-uniform in permeability and oil saturation by injecting a working agent into a formation through an injection well and extracting oil from a production well, characterized in that they create a difference in the dielectric constant of fluids located in the undrained and drained parts of the formation by injection as a working agent of the composition of physicochemical substances selected from the condition of creating a lower dielectric constant in the drained part of the formation compared to the non-drained hour water and in a volume excluding the entry of aggressive components of the composition to the bottom of the producing well.  2. The method according to claim 1, characterized in that as a component of the composition to reduce the dielectric constant use hydrochloric acid.