RU2527053C1 - Development method of fractured-porous types of reservoirs - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method comprises drilling producers and injectors, injecting water via injectors and withdrawing product via producers. According to the invention water is injected at the initial stage of development. When one of producers is flooded by the injected water up to 95%, the injector is identified where water is broken. To the water injected to this injector ash is added; ash is represented by remains of burn solid fuel with particle size of 70 mcm and concentration of 50 mg/l at the most. When water cut in the producer decreases per 25% or more water without ash is injected. These cycles are made for all watered wells and repeated till water cut after injection of water with ash decreases less than 95%.

EFFECT: increasing oil recovery factor of the productive stratum and reducing water cut rate of the product in producers.

1 tbl, 1 ex, 1 dwg

Description

The invention relates to the oil industry and may find application in the development of an oil reservoir of a predominantly hydrophobic fracture-pore reservoir.

A known method of developing oil fields, including processing the bottom-hole zone of a producing and / or injection well, injecting a hydrophobic material — hydrophobic chemically modified silica, a hydrocarbon liquid and an aqueous solution of hydrochloric acid into a formation, displacing oil from the reservoir and then delivering it from the bottom-hole zone according to the invention the injection of these reagents is carried out in one stage in the form of an invert acid microemulsion containing the specified silica with a discrete size particles of 0.005-0.1 microns in a concentration of 0.5-1.5 wt.% and additionally the microemulsion stability regulator is a surfactant. Additionally, the dispersion: dispersion phase of the microemulsion is from 1/1 to 3/1. The viscosity of the specified microemulsion in the range from 300 to 2500 MPa · s. The amount of the specified microemulsion in the range from 0.5 to 11 m ³ per 1 m opened by perforation of the effective thickness of the reservoir. When treating reservoirs with significant differences in the permeability of the interlayers, temporary isolation of highly permeable flooded areas is preliminarily carried out by injecting the indicated microemulsion with a viscosity of 2500-3500 mPa · s into the bottomhole zone of the formation (RF patent No. 2232262, class E21B 43/22, publ. July 10, 2004) .

The disadvantage of this method is the low oil recovery and high watering rate of products during the development of oil deposits, as well as significant costs for the event.

The closest in technical essence to the proposed method is a method for developing oil deposits in hydrophilic rocks-reservoirs, including drilling exploration wells and core sampling, according to the invention, core samples are taken from exploration wells from the reservoir, the rock wettability of the reservoir is measured, and its hydrophilicity is confirmed the development of the reservoir by the water flooding method is considered appropriate, then the capillary pressure of the beginning of oil displacement is determined by the core, a map of this pair is made meters and, based on the injection wells are placed in areas of relatively low capillary pressure values, enabling the displacement of oil from the pore spaces of the producing formation while flooding it (RF patent №2301883, Cl E21B 43/20, published 27.06.2007 -.. prototype).

The disadvantage of this method is the low oil recovery and high watering rate of products during the development of oil deposits containing hydrophobic zones.

The proposed invention solves the problem of increasing the oil recovery coefficient of the reservoir and reducing the watering rate of production wells.

The problem is solved in that in the method for developing a fracture-pore reservoir, including drilling production and injection wells, pumping water through injection wells and selecting products through production wells, according to the invention, water is initially pumped, after watering one of the production wells with water injected up to 95%, determine the injection well from which a water breakthrough occurred; ash is added to the water injected by this injection well, which is the remains of burning solid fuel, with a particle size of not more than 70 microns and with a concentration of not more than 50 mg / l, with a decrease in the water cut of the producing well by 25% or more, they switch to water injection without ash, the cycles are carried out with all flooded wells and repeated until until the water cut after pumping water with ash decreases below 95%.

SUMMARY OF THE INVENTION

When developing an oil deposit in a fracture-pore reservoir, mainly hydrophobic, water breaks through the cracks to the producing wells, while the capillary impregnation of the matrix and, accordingly, the displacement of oil from it is insignificant, which reduces the final oil recovery. There is a need for measures to change the wettability of the collector, to hydrophilize it. Existing technical solutions do not fully allow the efficient development of oil reserves from a matrix of a predominantly hydrophobic fractured-pore reservoir and change the reservoir wettability. One of the measures to change the wettability of the collector is to add ash to the pumped water, which is the residue from burning solid fuel. The proposed invention solves the problem of increasing the oil recovery coefficient of the reservoir and reducing the rate of watering of well products.

The problem is solved as follows.

Figure 1 presents a schematic representation of a section of a deposit in plan with the placement of wells. Designations: 1-4 - producing wells, 5 - injection well, Z - section of oil reservoir with a five-point element of wells 1-5, A - watering front by the time before the first ash injection cycle, B - watering front by the time before the second cycle ashes injection.

The method is implemented as follows.

According to the wettability index M, the rocks are classified as follows:

- hydrophobic rocks (M = 0-0.2);

- rocks are mainly hydrophobic (M = 0.21-0.4);

- rocks of intermediate wettability (M = 0.41-0.6);

- rocks are mainly hydrophilic (M = 0.61-0.8);

- hydrophilic rocks (M = 0.81-1).

If the fractured-pore reservoir of the oil reservoir is represented by a hydrophobic and / or predominantly hydrophobic reservoir, i.e. M less than 0.4, then its development is significantly complicated due to the breakthrough of water through cracks with a hydrophobic surface. Capillary impregnation of the matrix practically does not occur. According to laboratory studies of core samples of wells taken from such an oil reservoir, the wettability distribution of M. is determined. A collector with predominantly hydrophobic wettability is identified.

An oil reservoir is developed by producing and injection wells. In the process of development, a breakthrough of injected water from injection wells to production occurs. Section Z of the oil reservoir is represented by a five-point element with an injection well 5 in the center (Fig. 1). An analysis of the development of reserves of the Z section of the deposit developed by producing wells 1-4 showed that the water cut of the wells significantly outstrips the selection from the initial recoverable reserves (NCD). So for a well, for example, 1 water cut is more than 95%, while the selection from the NCD of this section Z is much lower. At this point, the distribution of the watering front A of wells 1-4 is shown in FIG.

Studies have shown that the high water cut of well 1 is not associated with annular flows. It is concluded that water broke through cracks from the injection wells to production 1. Next, by modeling the flow lines, it is determined that the cause of the watering of well 1 is injection well 5.

Conduct laboratory tests on cores taken from wells 1-5, for the displacement of oil by water with the addition of ash with different concentrations. It is established that the highest oil recovery factor for core samples, compared with water injection without ash, reaches at an ash concentration in water C, with C not more than 50 mg / l, because otherwise, according to research, a high concentration of particles clogs the pore channels of the reservoir. The particle size of the ash should also be no more than 70 microns, because according to studies, the average pore size of the formation in reservoirs of various types ranges from one to 70 microns (Tronov V.P. Water treatment of various types for use in the PPD system, 2001, pp. 4-9).

The chemical composition of the ash when burning various grades of solid fuels varies over a fairly wide range:

SiO ₂ = 10-68%,

Al ₂ O ₃ = 10-40%,

Fe ₂ O ₃ = 2-30%,

CuO = 2-70%,

MgO = 0-10%,

Na ₂ O + K ₂ O = 0-10%

(Pokrovsky V.N. Wastewater treatment of thermal power plants, 1980, p.20).

Ash pumped with concentration C is added to the water injected by injection well 5. A container with ash and a pump are installed at the mouth of injection well 5. The pump is connected to a water conduit that goes from the cluster pump station. From the tank, a metered supply of ash is carried out to the pump, where it is mixed with water.

According to studies, ash added to water allows hydrophilizing the surface of pores, channels, and reservoir cracks. Moreover, the particle size of the ash is quite small and is able to penetrate into the pore channels (at a concentration of C not more than 50 mg / l) and, especially, into cracks. There is a process of changing wettability at the molecular-ion level. As a result, water moving in cracks penetrates the reservoir matrix, displacing oil from it. If the matrix is also hydrophobic, like cracks, then the ash allows you to change the wettability of the pores themselves and, accordingly, better “leaches” the oil from the pores.

According to calculations, it is more optimal to start the process of pumping water with ash when the water cut of producing wells is not more than 95%, otherwise the final oil recovery coefficient is lower. The optimal period of water injection with ash is also, according to calculations, such a time at which the water cut of well production during the period of ash injection is reduced by 25% or more. With shorter times, the change in wettability does not occur in all the cracks along which water penetrates to the bottom of the producing wells from the injection.

Water is injected with ash until the water cut of well 1 decreases by more than 25% (after time T ₁ ). In the process of pumping ashes, water cut in wells 2-4 also decreases.

Next, they switch to pumping water without ash. After some time, for example, well 2 is watered. At this point, the distribution of the watering front B of the wells is shown in FIG. 1. By modeling the flow lines, it is again determined that the cause of the watering of well 2 is injection well 5. Ash with concentration C is again added to the water injected by injection well 5. After time T _{2, the} water content of well 2 is reduced by more than 25%. The water cut of wells 1, 3, 4 is also slightly reduced. Then they switch to water injection without ash.

These cycles are carried out with all flooded wells and repeated until the water cut after injection of water with ash decreases below 95%, because gradually the efficiency of each cycle decreases due to the fact that the front of the capillary impregnation of the matrix displaces mobile oil from it, and the water gradually passes to the faces of the producing wells.

The development is carried out until the full economically viable development of the site.

The result of the implementation of this method is to increase the oil recovery coefficient of the reservoir and reduce the rate of watering production of producing wells.

An example of a specific implementation of the method

According to laboratory studies of core samples taken from an oil reservoir with a fracture-pore reservoir, it was found that 62.2% of them have hydrophobic and predominantly hydrophobic wettability M (Table 1).

Table 1 The distribution of core samples by the value of the wettability index M, pcs. (%) 0-0.2 0.21-0.4 0.41-0.6 0.61-0.8 0.81-1.0 131 (46.3) 45 (15.9) 43 (15.2) 34 (12) 30 (10.6)

The reservoir is represented by a carbonate type of reservoir, massive structure, lies at a depth of 875 m, oil viscosity at reservoir conditions is 49.0 MPa · s, oil density at reservoir conditions is 879 kg / m ³ , initial reservoir temperature is 23 ° C, initial reservoir pressure - 7.1 MPa, matrix permeability - 177 MD, fracture permeability - 1 D, matrix porosity - 0.129, fracture porosity - 0.01, initial oil saturation - 0.816, average effective oil-saturated thickness - 10 m, water-oil contact is located at the absolute elevation - 543 m.

An oil reservoir is developed by producing and injection wells. Commercial water is pumped into part of the injection wells, and fresh water into part. In the process of development, a breakthrough of injected water from injection wells to production occurs. Section Z of the oil reservoir is represented by a five-point element with an injection well 5 in the center. The distance between the wells is 300-350 m. The analysis of the development of reserves of the Z section of the deposit (Fig. 1), developed by producing wells 1-4, showed that the water cut of the wells significantly outstrips the selection from the initial recoverable reserves. So, for two production wells 1 and 3, the water cut is 95.5% and 96.1%, respectively, while the selection from the NCD of this section Z is only 32.4%. At this point, the distribution of the watering front A of wells 1 and 3 is shown in FIG.

Studies have shown that the high water cut of wells 1 and 3 is not associated with annular flows. The conclusion is made that water broke through cracks from injection wells to production wells. Further, by modeling the flow lines, it is determined that the cause of the watering of wells 1 and 3 is the injection well 5, into which the produced water is pumped.

Conduct laboratory tests on cores taken from wells 1-5, for the displacement of oil by water with the addition of ash with different concentrations. Use the ash obtained by burning coal in thermal power plants. The ash composition is as follows: SiO ₂ = 44.5%, Al ₂ O ₃ = 35.0%, Fe ₂ O ₃ = 15.6%, CaO = 3.9%, MgO = 0.3%, other - 0, 7% It was found that the largest recovery factor for core samples, compared with water injection without ash, was achieved at an ash concentration in water of C = 10 mg / L. It is established that the pore size of the formation varies between 50-70 microns. Ashes are sifted through a vibrating screen up to 50 microns in size, and the required ash particle size is obtained.

In the water injected by injection well 5, ash is added with a concentration of C = 10 mg / L. At the mouth of the injection well 5, a container with ash and a pump are installed. The pump is connected to a water conduit that goes from the cluster pump station. From the tank, a metered supply of ash is carried out to the pump, where it is mixed with water.

The injectivity of injection well 5 is q = 20 m ³ / day. Then it is required to add m = C · q = 10 · 10 ^-6 · 20 · 10 ³ = 0.2 kg of ash per day. Water and ash are pumped until the water cut of the wells decreases by more than 25%. So, after T ₁ = 15 days of injection, the water cut of wells 1 and 3 fell to 70.5% and 64.1%, respectively. The water cut of wells 2 and 4, which was less than 95%, also decreased by 5.2% and 10.5%, respectively.

Next, they switch to pumping water without ash. Two years later, well 4 is flooded to 95.3%. At this point, the distribution of the watering front B of the well 4 is shown in FIG. By modeling the flow lines, it is determined that the cause of the watering of the well 4 is also the injection well 5. In the water injected by the injection well 5, ash is again added with a concentration of C = 10 mg / L. After T ₂ = 22 days, the water cut of well 4 decreased to 68.3%. The water cut of wells 1-3 also decreased slightly. Then they switch to pumping water without ash.

These cycles are carried out with all watering wells and repeated until the water cut after pumping water with ash decreases below 95%.

So, after 8 cycles of water injection with ash, the water cut of wells 1-4 does not fall below 95%, which indicates that the front of the capillary impregnation of the matrix practically displaced mobile oil from it. At this point, the selection from NCDs in section Z was 93.8%.

The development is carried out until the full economically viable development of the site.

As a result, from the considered section Z of the oil deposit during the time that was limited by watering all production wells to 98%, or by achieving a minimum profitable oil production rate of 1 well of 0.5 t / day, 129.6 thousand tons of oil were produced, oil recovery coefficient (CIN) was 0.341. According to the prototype, ceteris paribus, 99.9 thousand tons of oil was produced, oil recovery factor - 0.263. The increase in CIN amounted to 0.078.

The application of the proposed method allows to increase the oil recovery coefficient of the reservoir and to reduce the rate of watering production wells.

Claims (1)

A method for developing a fracture-pore reservoir, including drilling production and injection wells, pumping water through injection wells and selecting products through production wells, characterized in that water is pumped at the initial stage, after the flooding of one of the production wells with injected water, up to 95% determine the injection well , from which a water breakthrough occurred, ash is added to the water injected by this injection well, which is the remains of burning solid fuel with particle sizes not large e 70 microns and with a concentration of not more than 50 mg / l, with a decrease in water cut of the producing well by 25% or more, they switch to water without ash, the cycles are carried out with all water wells and repeated until water cut after water with ash is not will decrease below 95%.

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