RU1633875C - Method for developing oil bed of inhomogeneous permeability - Google Patents

Abstract

FIELD: oil-producing industry. SUBSTANCE: aqueous solution of aluminium salt is injected cyclically by portions into the bed (wt.-% in terms of aluminium oxide). First portion with a concentration 1.25 -24.7 is injected until pressure becomes 1.2 - 1.5 times higher than the initial pressure, the second portion, with a concentration of 0.005-1.24. The beds with a carbonate content below 2% are additionally injected with the salt of carbonic acid at a mass relation of aluminium salt and salt of carbonic acid of 0.17-0.90. The mass relation of said salts is selected so as to ensure that the injection time would be shorter than the time of induction period of gel formation. The injection time τ is calculated by the formula t=24V/Q where V - volume of highly-permeable flooded bed zone, m³; Q - efficiency of pressure plate, m³/ d. Method increases the coefficient before oil washing from 4.8 to 9.9% as compared with the known method. EFFECT: higher efficiency of method achieved by increased flooding of bed. 4 tbl

Description

 The invention relates to the oil industry, in particular to methods for developing fields with heterogeneous formations at a late stage.

 The purpose of the method is to increase its effectiveness by increasing the coverage of the formation by displacement.

 The method is as follows.

 A complex of geological, physical and hydrodynamic studies is carried out on a waterlogged oil reservoir represented by heterogeneous permeability reservoirs, the results of which determine the presence, position and approximate size of highly permeable reservoir zones, as well as the carbonate of the reservoir rock.

, где τ - время закачки, ч;
V - объем высокопроницаемой обводненной зоны, м³;
Q - приемистость нагнетательной скважины, м³/сут.An aqueous solution of an aluminum salt of variable concentration (wt.% In terms of alumina) is cyclically pumped into the formation in portions: the first portion with a concentration of 1.25-24.7 is pumped into the formation to a pressure of 1.2-1.5 times higher than with the initial, second portion with a concentration of 0.005-1.24; moreover, in the formations with a carbonate content of less than 2%, an additional salt of carbonic acid is injected at a mass ratio of aluminum salt (in terms of aluminum oxide) and a salt of carbonic acid from 0.17 to 0.90, while the mass ratio of aluminum salt and carbonic salt is chosen so that the injection time of the reagents is less than the time of the induction period of gelation corresponding to this ratio of salts. Download time is calculated by the formula
τ =

where τ is the injection time, h;
V is the volume of highly permeable waterlogged zone, m ³ ;
Q - injectivity of the injection well, m ³ / day.

 If there is a water-soluble carbonic acid salt, the reagent solutions (carbonic acid salts and aluminum salts) are prepared separately, in two containers, then they are pumped simultaneously and separately into the injection well with the help of a pump unit: one solution through tubing, the other through annulus. When using water-insoluble salts of carbonic acid, the reagents (salts and water) are introduced into one container and mixed until a homogeneous suspension is formed. The suspension is pumped by a pumping unit into an injection well.

 Throughout the entire injection process, the injection pressure is monitored.

 The choice of the ratio of aluminum salt to carbonic salt within the range specified in the claims depends on the injection time of the reagents, which is determined by the volume of the highly permeable zone (C) and the injectivity of the injection well (Q).

, затем по таблице 2 выбирают такое количественное соотношение соли алюминия и соли угольной кислоты, которому соответствует индукционный период τ_инд, не меньший времени закачки ( τ_зак), т.е. чтобы выполнялось условие
τ_зак≅ τ_инд, или

≅ τ_инд
Эффективность данного способа в сравнении с известным проверяют в лабораторных условиях.Based on the maximum filling of the highly permeable zone with gel, the volumes of injected reagents (a highly concentrated solution of aluminum salt and carbonic acid salt) are taken equal to the volume of the highly permeable zone. Knowing the injectivity of the injection well, the time required to pump the set volume of reagents (τ _zak ) is calculated using the formula τ _zak =

, then, according to Table 2, such a quantitative ratio of aluminum salt and carbonic acid salt is selected, which corresponds to the induction period τ _ind , not less than the injection time (τ _zak ), i.e. to satisfy the condition
τ _zak ≅ τ _ind , or

≅ τ _ind
The effectiveness of this method in comparison with the known is checked in laboratory conditions.

During the test, aluminum oxychloride Al (OH) ₂ Cl (OXA) is used as aluminum salts - a powdery substance, highly soluble in water, a waste product with a basic substance content of 25% (in terms of Al ₂ O ₃ ), aluminum chloride - AlCl ₃ ˙6H ₂ O - highly hygroscopic small crystals of white color, highly soluble in water, technical alumina sulfate - Al ₂ (SO ₄ ) ₃ ˙18H ₂ O - white crystals, highly soluble in water, calcium carbonate CaCO as salts of carbonic acid ₃ - fine white powder, insoluble in water, sodium carbonate Na ₂ CO ₃ - white powder, soluble in water, mineralized water with a salt content of up to 100 g / l and technical.

 At the first stage of laboratory research, the conditions of gel formation in the free volume are studied. To do this, carbonic acid salts are added to glasses with solutions of aluminum salts of various concentrations, the mixture is stirred, and they are left alone at room temperature for 24 hours, fixing the onset of sediment formation and its type (flocculent or gel-like).

 As a result of the studies, it was found that in solutions of aluminum salts with a concentration of 0.005-1.24 wt.% Alumina mixed with carbonic salts in any ratio range, small flakes are formed, which eventually settle to the bottom, however, the precipitate remains discrete . In solutions of aluminum salts in the concentration range 1.25-24.7 wt.% On aluminum oxide when carbonic acid salts are added to them, in some cases the formation of flakes and water, in some cases, a thick gel in the entire volume of the mixture, in some, a mixture remains unchanged. To clarify the area of gelation, experiments were carried out with solutions of aluminum salts in the concentration range 1.25-24.7%. Sodium carbonate is used as the carbonic acid salt. The results are presented in table 1.

 All aluminum salts are capable of gelation in the presence of carbonic acid salts in a certain range of mass ratios of aluminum salts and carbonic salts: for aluminum sulfate in the range of 0.31-0.38; for aluminum chloride 0.17-0.38; for oxychloride 0.22-0.90. Below the specified limits, an amorphous precipitate forms; above, the system remains unchanged. Therefore, 0.17 was taken as the lower limit of the mass ratio of aluminum salt and carbonic acid salt, and 0.90 as the upper one. The resulting gels are a thick gel-like mass with increasing viscosity over time. The viscosity of the gel depends not only on time, but also on the initial concentration and ratio of the amounts of aluminum salt and carbonic acid salt: with an increase in these amounts, the viscosity increases, reaching 1000 MPa s. Gels are stable in both fresh and mineralized water.

 Aluminum sulfate does not form a gel with calcium carbonate, as water-insoluble calcium sulfate formed in the initial stage blocks particles of calcium carbonate, thereby interrupting the hydrolysis reaction.

 As a result of laboratory studies, it was found that the induction period of gelation increases with an increase in the mass ratio of aluminum salt and carbonic acid salt (Table 2).

 When replacing water-insoluble salts of carbonic acid with water-soluble, the induction period is reduced to several hours.

 The method of introducing a carbonic acid salt into an aluminum salt solution — in the form of a dry powder or in the aqueous phase — does not matter.

Полученные данные приведены в табл.3.In order to more closely approximate laboratory conditions to field conditions, the gelation process is studied on samples of natural cores with a diameter d, length l, and a cross-sectional area F. For this, 3-4 pore volumes of water are first passed through the core, then 1 pore volume of a solution of aluminum salt and coal salt acids, leave the core for 1 day, alone, and then continue to filter water through it, fixing at each stage the pressure drop (ΔP) at a given flow rate. Then, based on these data, core conductivity (K _prov ) is calculated by the formula
K _prov =

The data obtained are given in table.3.

 The effectiveness of the method in comparison with the known is studied on artificial reservoir models, which are a system of two elements, which are glass tubes 30 cm long, 2 cm in diameter, filled with quartz sand, while one element (A) has a permeability 10 times higher than the other (B), which is achieved by selecting the appropriate fractions of sand. The experiments are carried out in the following sequence.

 The porous medium of each element is individually saturated with oil, then the elements in the model are connected so that it has one common input and separate outputs from each element. Oil is displaced from each model by water to a water cut of 98-99% at the outlet of the element with high permeability. At the input of model No. 1, a rim of a 0.05% solution of aluminum sulfate is fed in an amount of 0.01 pore volume of the model (known method). The rim of the solution containing 10% aluminum sulfate and 4% sodium carbonate, i.e. their ratio is 0.79, and they leave it alone for 3 days, and then the rim of a 0.05% solution of aluminum sulfate (0.1 pore volume) of 10%.

 Oil is displaced by water from both models and the volume of oil is measured at the outlet.

100; K₂=

100;
ΔK =

100; K_1Σ=

100;
K_2Σ=

100, где К₁ и К₂ - начальный и конечный коэффициенты вытеснения, %; причем К_1А и Е_2А - отдельно по элементу А; К_1Б и К_2Б - отдельно по элементу Б; K_1Σ и K_2Σ - по модели в целом; V_o - начальный объем нефти в пористой среде, мл; V₁ - объем нефти, вытесненной первично водой, мл; V₂ - объем нефти, вытесненной при доотмыве, мл; Δ К - абсолютный прирост коэффициента вытеснения, %.Processing the results of experiments is carried out according to the formulas:
K ₁ =

100; K ₂ =

100;
ΔK =

100; K _1Σ =

100;
K _2Σ =

100, where K ₁ and K ₂ are the initial and final displacement factors,%; moreover, K _1A and E _2A - separately for element A; K _1B and K _2B - separately for element B; K _1Σ and K _2Σ - according to the model as a whole; V _o - the initial volume of oil in a porous medium, ml; V ₁ - the volume of oil displaced primarily by water, ml; V ₂ - the volume of oil displaced during re-washing, ml; Δ K is the absolute increase in the displacement coefficient,%.

 An example implementation of the method.

The volume of the highly permeable zone, determined by the results of hydrodynamic and geological studies, is 700 m ³ . The injectivity of the injection well (Q) is 100 m ³ / s. It takes 7 days or 168 hours to pump a predetermined volume of reagents. According to Table 2, the ratio of aluminum salt to carbonic acid salt with a gelation time greater than or equal to the injection time of 192 hours is selected. A reagent ratio of 0.90 corresponds to this induction period. With this ratio, gelation will begin only after the completion of the injection.

 In order to complete gelation, after injection of a concentrated solution of aluminum salt and, if necessary, carbonic acid salt, the injection well is stopped for 3 days. After this period, water is pumped into the well and the injection pressure is compared with the initial one. If the water injection pressure after the reagent rim exceeds the initial one by at least 1.2 times (which guarantees the reliability of the data obtained), then the second rim of the aluminum salt is pumped in an amount of up to 10% pore volume. If the pressure of water injection after injection of reagents remained at the initial level, then water injection is stopped and an additional volume of highly concentrated aluminum salt and, if necessary, carbonic acid salt are pumped into the well. Also leave the well for 3 days. , and then the gelation efficiency is determined by the pressure of water injection into it.

 The upper limit of excess discharge pressure (1.5 from the initial) is due to the strength characteristics of oilfield equipment; exceeding this limit can lead to emergency situations.

 After the injection of the second rim of the aluminum salt, the well is connected to the water conduit and oil is displaced from the low-permeability zones by water.

 The results of the experiments on oil displacement are presented in table 4.

 As can be seen from the results, the use of this method allows to increase the coefficient of additional washing of oil from the flooded porous medium compared with the known method from 4.8 to 9.9%.

Claims (2)

1. A METHOD FOR DEVELOPING AN INHOMOGENEOUS PERMEABILITY OF A WATERFLATED LAYER, which includes injecting an aqueous solution of an aluminum salt and water into a formation through an injection well, and selecting oil through a producing well, characterized in that, in order to increase the efficiency of the method by increasing the coverage of the formation by displacement, injecting water the aluminum salt solution is carried out in portions, the first portion with a concentration in terms of aluminum oxide of 1.25 - 24.7 wt.% is pumped into the reservoir to increase the initial pressure by 1.2 - 1.5 times, the second portion is pumped with ontsentratsiey 0.005 - 1.24 wt. %, and the injection time of an aqueous solution of aluminum salt is set less than the induction period of gelation time and calculated by the formula
τ _zak =

where τ _Zack - the time of injection of the reagents, h;
V is the volume of highly permeable waterlogged zone, m ³ ;
Q - injectivity of the injection well, m ³ / day.  2. The method according to claim 1, characterized in that, in order to develop formations with a carbonate content of less than 2%, an additional carbonic salt is pumped into the formation at a mass ratio of aluminum salt and carbonic acid salt of 0.17-0.90.

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