RU2187628C1 - Method of development of water-encroached oil pool with nonuniform geological structure - Google Patents

Abstract

FIELD: oil and gas producing industry; methods of increase of oil recovery from formations and reduction of producing well water-encroachment. SUBSTANCE: method includes injection into formation through injection well of aqueous solution of alkali metal silicate and oil withdrawal through producing wells. Additionally injected together are aqueous solutions of ammonium sulfate and calcium chloride whose reaction results in precipitation of calcium sulfate and ammonium chloride in dissolved state. Then, injected into formation is aqueous solution of alkali metal silicate which forms, together with ammonium chloride, bulky sediment of silicon oxide. Injected additionally into formation is gel-forming solution based on aqueous solution of alkali metal silicate and ammonium sulfate. EFFECT: increased oil recovery from formation, reduced water cutting of produced oil due to additional isolation of nonuniform and high-permeability formations with reduced consumption of reagents. 2 cl, 1 tbl

Description

 The invention relates to the oil industry, in particular to methods for increasing oil recovery and reducing water cut in a producing well.

 There is a method of developing a flooded oil reservoir, the essence of which is the cyclic injection of aqueous solutions of calcium chloride and soda ash [1].

 The disadvantage of this method is its lack of effectiveness, since the interaction of the injected solutions results in a precipitate in the form of a fine suspension of calcium carbonate, easily washed out of the washed and fractured zones of the formation, and the effect can be obtained using highly concentrated solutions (19-21 wt.%).

 The closest solution taken as a prototype is a method of developing an irrigated oil reservoir that is heterogeneous in geological structure, which consists in sequentially injecting an aqueous solution of ammonium chloride and an aqueous solution of alkali metal silicate into the formation [2].

 The disadvantage of this method is the low efficiency in the isolation of heterogeneous permeability formations, highly permeable and fractured zones of the formation.

 The objective of the invention is to increase oil recovery and reduce water cut of produced oil due to the additional isolation of heterogeneous and highly permeable formations while reducing the consumption of reagents.

 The problem is solved in that in a method for developing an irrigated oil reservoir that is heterogeneous in geological structure, including injecting an aqueous solution of alkali metal silicate through injection wells and producing oil through production wells, according to the invention, aqueous solutions of ammonium sulfate are additionally simultaneously injected into the formation and calcium chloride, during the interaction of which a precipitate of calcium sulfate and dissolved ammonium chloride are formed in the formation, then they are pumped into the formation in projectile loader alkali metal silicate solution, forming ammonium chloride voluminous precipitate silica.

 In order to increase the efficiency of the screen created for the redistribution of formation fluids, a gel-forming solution based on aqueous solutions of alkali metal silicate and ammonium sulfate is additionally pumped into the formation.

 The essence of the invention lies in the fact that a solution of ammonium sulfate and a solution of calcium chloride are pumped into the well at the same time. In the process of injection, the solutions are mixed and react with each other, forming calcium sulfate and ammonium chloride. Calcium sulfate, precipitated in the form of a fine dispersion, is pumped further into the reservoir and blocks part of the volume of the pore channels. The rest of the pore channel is filled with a solution of ammonium chloride, which is in the reservoir in a dissolved form, which can be used to obtain a precipitate of silicon oxide during the subsequent injection of an aqueous solution of alkali metal silicate, for example sodium silicate. This creates an insulating screen that prevents the leaching of finely dispersed precipitate of calcium sulfate (gypsum), which allows you to more fully close cracks and permeable zones and increase filtration resistance.

 The chemical processes for producing precipitation in two stages are presented below.

2. Получение осадка окиси кремния

Для изоляции наиболее проницаемых зон и зон поглощения предусмотрена закачка гелеобразующего раствора на основе силиката щелочного металла и сульфата аммония, при этом их водные растворы имеют следующие концентрации:
3-20% Na₂SiO₃, 0,5-2,5% (NH₄)₂SO₄. Схематично реакцию получения геля можно представить следующим образом:
nNa₂SiO₃+m(NH₄)₂SO₄+H₂O-->-[SiO₂]_n-+NH₄OH+NaOH+Na₂SO₄.1. The stage of obtaining the precipitate in the form of gypsum

2. Obtaining a precipitate of silicon oxide

To isolate the most permeable zones and absorption zones, an injection of a gelling solution based on alkali metal silicate and ammonium sulfate is provided, while their aqueous solutions have the following concentrations:
3-20% Na ₂ SiO ₃ , 0.5-2.5% (NH ₄ ) ₂ SO ₄ . Schematically, the gel production reaction can be represented as follows:
nNa ₂ SiO ₃ + m (NH ₄ ) ₂ SO ₄ + H ₂ O -> - [SiO ₂ ] _n - + NH ₄ OH + NaOH + Na ₂ SO ₄ .

 The gelling solution has a low viscosity (5-10 MPa • s), is easily pumped into the reservoir. In the formation at an elevated temperature, a cross-linked viscoelastic gel is formed, which includes in its volume and fixes the previously obtained sediments. The result is a screen that reliably isolates the washed zones and flows.

As can be seen from the reaction equations, after the interaction of the reagents, the fluid remains in the formation with a highly alkaline medium, since it contains ammonium hydroxide NH ₄ OH and sodium hydroxide NaOH. Further, during the injection of the displacing agent, a process similar to alkaline water flooding occurs. An alkaline solution improves the wettability of oil-saturated interlayers, promotes the washing of oil and, ultimately, an increase in oil recovery.

 To determine in laboratory conditions the amount of precipitate obtained by the interaction of ammonium sulfate, calcium chloride and alkali metal silicate, the following studies were carried out. Solutions with various concentrations of the above substances were prepared. To exclude the influence of the sedimentation factor at different densities of the dispersion medium, the solutions were centrifuged in graduated tubes, then the volume of the precipitate formed and the pH of the filtrate were determined. The filtrates were selected to study their laundering ability. The washing ability was also determined by centrifugation. 5 g of oil-saturated core were taken into graduated centrifuge tubes, poured with filtrates and placed in a centrifuge. The determination was carried out according to standard methods.

 The results of laboratory studies for the implementation of the proposed method are presented in the table, which shows that the sequence of sediment and its amount will provide more efficient isolation of highly permeable zones compared to the prototype.

 The table shows that the washing of oil by filtrate by the proposed method is higher than by the prototype.

The gel-forming solution based on alkali metal silicate and ammonium sulfate for hardening the insulating screen has the following technological parameters: gelation time at a temperature of 20 ^o C 5-72 hours, at a temperature of 70 ^o C 0.5-10 hours, the viscosity of the working solution 5-12 MPa • s, strength on SNA 450-850 Pa, thermal stability> 10 months.

 The technology for the injection of sediment-forming compounds: a solution of ammonium sulfate and a solution of calcium chloride at the same time, is pumped into the well through a hydroactivator, then a solution of sodium silicate is pumped into the formation.

 The optimal calculation of the injection of these solutions is determined by generally accepted methods, taking into account the physicochemical and geological features of the formation, and can range from several tens to several hundred cubic meters.

 Solutions can be injected in one or several cycles, each of which includes the injection of all three solutions and, if necessary, fixing the rim of the gelling solution.

 Gelling solution injection technology: working solutions of sodium silicate and ammonium sulfate are pumped in two parallel streams through a standard tee or hydraulic activator and kept in the formation for gelation.

The inventive method provides reliable isolation of formations having a heterogeneous reservoir, washed zones with high permeability and fracture. The method can be implemented in a wide temperature range from 20 to 100 ^o C.

Sources of information
1. RF Patent 2039224, IPC E 21 B 43/22, 33/138, 1995.

 2. RF Patent 2096602, IPC E 21 B 43/22, 1997 - PROTOTYPE.

Claims (2)

 1. A method of developing an irrigated oil reservoir that is heterogeneous in geological structure, including injecting an aqueous solution of an alkali metal silicate through injection wells and producing oil through production wells, characterized in that the aqueous solutions of ammonium sulfate and calcium chloride are additionally injected into the formation, during the interaction of which a precipitate of calcium sulfate is formed in the formation and ammonium chloride is dissolved, then an aqueous solution of alkali metal silicate is pumped into the formation, Braz with ammonium chloride voluminous precipitate silica.  2. The method according to claim 1, characterized in that a gelling solution based on aqueous solutions of alkali metal silicate and ammonium sulfate is further pumped into the formation.

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