RU2623409C1 - Procedure for development of deposit of oil in carbonate collectors - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: according to the method, the accumulation is drilled with wells by one of the known grids. Displacement agent is injected to injectors with pressure control and recovery of products through producers are carried out. Hydrodynamic studies are carried out in the watering producers. The graphs of the indicator curves are plotted, on these graphs the drop point of the watercut is determined as the watercut curve inflection point. The point of intersection of the pressure line of oil saturation with a gas with a watercut curve is determined. The optimum operation mode of producers at the natural depletion mode is taken in the extraction zone below the healing breakdown pressure point and above the bubble point. In the fracture system, accumulations are maintained at a lower pressure than over the rest area of the accumulation.

EFFECT: increase of oil recovery and efficiency of oil-pool development in carbonate reservoirs with low water flooding.

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Description

The proposed method relates to the oil industry, in particular to the field of development of oil deposits in carbonate reservoirs.

A known method for the development of fractured reservoirs (RF patent No. 2526082, ЕВВ 43/20, publ. 08/20/2014, bull. No. 23), including the determination of fracture or decompression lines of the reservoir, the construction of production and injection wells taking into account the fracture of the reservoir, injection of the displacing agent in injection wells and oil extraction through production wells. Then, a section of the reservoir is selected for development with oil-saturated thicknesses of more than 10 m, preventing rapid watering of the produced oil, and the location of decompression nodes — intersections of decompression lines — is determined. Production vertical or lateral, lateral horizontal wells are drilled along an uneven grid with penetration into decompression units, and injection wells are located in compacted carbonate reservoirs with minimal and medium fracturing, between several decompression units at approximately equal distance from them.

The disadvantage of this method is that in the process of producing wells do not determine the closing pressure of the cracks in the reservoir and do not maintain the pressure at the bottom above the level of the closing pressure of the cracks, which leads to a decrease in the flow rate of oil wells and lower oil recovery in the whole reservoir. The pressure of injection of the displacing agent in the wells is not set below the pressure of the beginning of the opening of cracks in the reservoir, which leads to a sharp increase in water cut in the well and a decrease in oil production.

The closest in technical essence is the method of development of oil reservoirs, which are non-uniform in reservoir properties (RF patent No. 2046181, ЕВВ 43/20, publ. 10/20/95, bull. No. 29), including drilling a reservoir according to the design grid of wells, conducting geophysical, hydrodynamic and laboratory studies, the selection of hydrocarbons in the mode of depletion of reservoir energy and the subsequent injection of a displacing agent into zones of low permeability. The injection of the displacing agent is carried out after reducing the reservoir pressure to the initial shear pressure of the oil between the selection zones and the aquifer. Wells are being mastered for injection of the displacing agent, which have the highest rate of reservoir pressure drop and the lowest hydraulic conductivity in the deposits. As the reservoir pressure is restored through the reservoir, additional wells with the lowest rate of reservoir pressure recovery and the lowest hydraulic conductivity are being developed for injection of the displacing agent.

The disadvantage of this method is that in the process of producing wells do not determine the closing pressure of the cracks in the reservoir and do not maintain the pressure at the bottom above the level of the closing pressure of the cracks, which leads to a drop in oil production and lower oil recovery. The injection pressure in the deposits is not regulated, it is not set below the pressure at the beginning of crack opening, which leads to a decrease in oil production as a result of sharp watering of the wells.

The technical task of the proposed method is to increase oil recovery and the efficiency of the development of oil deposits in carbonate reservoirs at low pressure flooding by regulating the discharge pressure of the displacing agent in the reservoir and the pressure on the bottom of production wells.

The technical result is achieved by a method of developing an oil deposit in carbonate reservoirs, including drilling a deposit in wells according to one of the known grids, pumping a displacing agent into injection wells with pressure control, and selecting products from production wells.

What is new is that hydrodynamic studies are carried out in irrigated production wells, graphs of indicator curves are constructed on which the water cut reduction point is determined as the inflection point of the water cut curve, the intersection point of the oil saturation pressure line with gas and the water cut curve is determined, and the optimal operating mode of production wells on natural depletion in the selection zone below the critical point of crack closure and above the pressure point of oil saturation with gas, while in the system deposit Shin support a lower pressure than the rest of the deposit area.

In FIG. 1 presents a diagram of the implementation of the proposed method for the development of oil deposits (top view) on the site deposits. In FIG. 2 shows the dependence of fluid production on reservoir pressure in the production well selection zone. In FIG. Figure 3 shows the dependence of the injection volume of the displacing agent on the bottomhole pressure of injection wells.

The inventive method is carried out in the following sequence.

Deposit 1 (Fig. 1) of oil is drilled by wells 2-13 according to a known grid. The geological structure of the oil reservoir 1 is specified, the porosity, permeability of the reservoirs, rock pressure in the reservoir 1 are determined, hydrodynamic studies are carried out in wells to determine the reservoir, bottomhole pressure and the saturation pressure Рн (Fig. 2) of oil by gas. Produce products from producing wells 2-13. Wells at the initial stage of development work on a natural mode of depletion.

The development of carbonate fractured reservoirs in the natural mode of depletion leads to a gradual decrease in reservoir pressure, pressure at the bottom of production wells, in the zone of formation fluid extraction. During the operation of producing wells 3, 8, 10 (Fig. 1), the water cut of the product begins to increase, and then, as the reservoir pressure decreases, it decreases to the original and lower, which indicates the existence of a hydrodynamic connection in the oil reservoir 1. Formation pressure of the beginning of water cut reduction corresponds to the pressure of the beginning of closure of cracks along which formation fluid flows. A further decrease in pressure in the selection zone leads to a decrease in oil production rates and water cut.

To determine the optimal mode of maintaining pressure in the selection zone, hydrodynamic studies are carried out in flooded producing wells 3, 8, 10, then graphs of indicator curves 14 are constructed from the results obtained (Fig. 2). On the curves, point A of the beginning of the reduction in water cut is determined. This point is located at the inflection point 16 of the water cut curve and is the beginning of the critical pressure zone l of the fracture closure. The point P of the intersection of the saturation pressure line PH of oil with gas with the water cut curve 14 is determined.

According to the graph of indicator curves for the optimal operation of producing wells 2-13 (Fig. 1) in the natural mode of depletion, it is necessary to maintain the pressure in the extraction zone in the interval l (Fig. 2) from 4.6 to 2.4 MPa, i.e. below point A of the critical crack closure pressure and above point P the saturation pressure P of oil by gas. With a decrease in reservoir pressure below the saturation pressure RN of oil with gas, gas is released from the oil into the reservoir and the viscosity of the oil increases, which leads to a sharp decrease in oil production.

With a decrease in reservoir pressure in the selection zone of production wells 3, 8, 10 (Fig. 1) to the extent of the closure of the cracks, poorly developed wells 3, 8, 10 are developed in turn under injection of the displacing agent.

The most rational conditions for the development of carbonate fractured reservoirs are to maintain a lower pressure in the fracture system than in the rest of the oil reservoir 1. The reservoir pressure in the selection zone, exceeding the critical, i.e. the pressure at the beginning of crack opening significantly complicates the development of reservoir 1, since the risk of formation water flowing through the cracks to the intervals of well perforation and rapid flooding of the produced products increases.

The bottomhole pressure in injection wells 3, 8, 10 should not exceed the crack opening pressure in the reservoir in order to avoid uneven oil displacement by water and a decrease in oil flow rate in the total fluid withdrawal from production wells 2, 4-7, 9, 11-13.

To determine the optimal values of the bottomhole injection pressures, hydrodynamic studies are carried out in wells 3, 8, 10. Using the results obtained, graphs of indicator curves 17 (Fig. 3) are constructed that have characteristic inflection points 18. On the curves, the point B at the beginning of a sharp increase in water cut is determined, which corresponds to the inflection point 18 of the water cut curve and is the boundary of the critical crack opening pressure zone d . The injection pressure at the bottom of wells 3, 8, 10 (Fig. 1), corresponding to the value of point B on the indicator curve, is the maximum allowable for oil reservoir 1 (Fig. 1), since with a further increase in the injection pressure of the displacing agent, the existing or the formation of new cracks.

Thus, according to the graph of the indicator curves 17 (Fig. 3), the optimum allowable bottomhole discharge pressure must be maintained in the interval c , i.e. above the reservoir pressure of the reservoir and below point B of the critical crack opening pressure.

Point B on the indicator curve is critical and indicates that with a further increase in the injection pressure in wells 3, 8, 10 (Fig. 1), there will be a sharp increase in the flooding of produced products in producing wells 2, 4-7, 9, 11-13 as a result of the displacement agent entering the open cracks to the perforation intervals.

The development of oil deposits in carbonate reservoirs is carried out at low-pressure flooding, which stabilizes reservoir energy by regulating the pressure of injection of the displacing agent into injection wells 3, 8, 10 of oil reservoir 1 and pressure in the extraction zone of production wells 2, 4-7, 9, 11- 13.

An example of a specific implementation.

The implementation of this method, consider the example of a massive reservoir of 1 oil in Tournaisian carbonate reservoirs.

The oil deposit was drilled with wells on a 300 × 300 m grid. Based on the results of studies of wells 2-13 drilled in reservoir 1, the following data were obtained: reservoir permeability - 0.064 μm ² , porosity - 12.0%, reservoir pressure - 9.8 MPa, mountain pressure - 24.4 MPa, oil saturation pressure of gas - 2.4 MPa, water cut of produced products does not exceed 5.7%.

Production wells 2-13 were put into operation on a natural depletion mode. After six months of operation in well selection zone 3, the pressure decreased to 7.1 MPa, which amounted to 0.29 units. from mining, and the water cut of products increased to 35.0%. Over the next five months, pressure in well selection zone 3 continued to decrease gradually. The water cut, reaching a maximum value of 44.3% at a reservoir pressure of 6.5 MPa (0.26 units from the mountain), also began to decrease.

In well 3 conducted hydrodynamic studies. According to the obtained results, graphs of indicator curves 14 were constructed (Fig. 2). On curve 15, point A of the beginning of the reduction in water cut was determined, which corresponds to the inflection point 16 of the curve of water cut 15 and is the beginning of the critical contact zone l of the fracture closure. On the saturation pressure line Рн of oil with gas, the point Р of intersection with the water cut curve 14 was determined.

According to the graph of indicator curves 14 (Fig. 2) for optimal operation of producing wells 2-13 (Fig. 1) in a natural depletion mode, it is necessary to maintain pressure in the selection zone of wells 2-13 in the range from 4.6 to 2.4 MPa, t .e. below the closing pressure of the cracks and above the saturation pressure Rn (Fig. 2) of oil by gas.

After nine months of operation of production well 3 (Fig. 1), the oil production rate decreased from 5.2 to 1.1 t / day, as a result of which well 3, as unprofitable, was transferred to displacing the displacing agent.

The optimal value of the bottomhole injection pressure in well 3 was determined by the results of hydrodynamic studies, for which a plot of indicator curve 17 (Fig. 3) was constructed, which has a characteristic inflection point 18. This point corresponds to point B of the beginning of a sharp increase in water cut and is the beginning of critical pressure zone d crack opening. The discharge pressure at point B is 14.6 MPa or 0.6 units. from rock pressure, which corresponds to the beginning of a spasmodic increase in water cut and is the maximum allowable for reservoir 1 (Fig. 1) of oil.

Thus, according to the graph of the indicator curves, the optimum allowable bottomhole injection pressure in the well 3 must be maintained in the interval with (Fig. 3), i.e. above the reservoir pressure of 9.8 MPa or 0.48 of rock pressure and below point B of the critical crack opening pressure of 14.6 MPa or 0.6 units from rock pressure. Similarly, wells 8 and 10 (Fig. 1) were transferred from production to injection.

As a result of the application of the method for developing oil deposits in carbonate reservoirs, the anhydrous period of operation of production wells increased to six months,

oil recovery increased 1.1 times compared with conventional waterflooding, compensation for the selection of reservoir fluid by injection of a displacing agent was more than 90%.

The proposed method increases the coverage of oil deposits in carbonate reservoirs by water flooding, increases oil recovery and reservoir development efficiency at low-pressure flooding, which allows to regulate the pressure of the displacing agent discharge into the deposits and the pressure on the bottom of production wells.

Claims (1)

A method of developing an oil deposit in carbonate reservoirs, including drilling a deposit in wells according to one of the known grids, pumping a displacing agent into injection wells with pressure control and selecting products from production wells, characterized in that hydrodynamic studies are carried out in irrigated production wells, and graphs of indicator curves are constructed on which the water cut reduction point is determined as the inflection point of the water cut curve, the intersection point of the oil saturation pressure line ha At the same time, they take the water cut curve and take the optimal mode of operation of the production wells in the natural mode of depletion in the selection zone below the critical point of fracture closure and above the point of oil saturation pressure with gas, while the reservoir pressure system maintains a lower pressure than the rest of the reservoir area.

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