RU2520997C1 - Method for development of separate small oil lenses - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: while developing separate small oil lenses penetrated by a single well extraction of the formation fluid is alternated with injection of a displacement agent. Injection of a displacement agent is made at pressure that does not exceed breakdown pressure determined against geological and physical parameters of the lens until intake reduces per 50% in comparison with the initial value. Fluid extraction is made till the oil production rate decreases per 20-60% in comparison with the initial value. At that injection periods at the initial stage are made through equal time intervals until formation pressure reaches the initial value. Extraction periods at the initial stage are also made in equal time intervals until formation pressure reduces up to 80-90% of bubble point pressure. At that the initial development stage is considered completed when the initial oil production rate decreases in the second and next extraction cycles up to 30-60% of the initial oil production rate in the first cycle.

EFFECT: improvement of the formation oil recovery due to changes in extraction and injection modes.

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Description

The invention relates to the oil industry, in particular to the development of lithologically shielded oil deposits.

There is a method of developing lithologically shielded oil-saturated lenses in one well, which includes alternating the injection of water with hydraulic fracturing of the porous medium and adjustable pressure relief and formation fluid withdrawal. Water is pumped at a pressure at the bottom of the borehole that exceeds the fracture pressure of the porous medium and is sufficient to create vertical cracks deeply penetrating into the formation to the lens boundaries. Stop the injection of water when the reservoir pressure is restored to its original level. Quickly relieve pressure on the bottom of the well. The well is converted for production and reservoir fluid is taken until the reservoir pressure drops to the level of oil saturation with gas or the oil production rate drops to the most profitable (RF patent No. 2150578, IPC ЕВВ 43/20, published on June 10, 2000).

The known method allows for the alternation of injection and extraction and to increase oil recovery, however, a significant part of the oil reserves remains undeveloped, because changes in reservoir properties during development are not taken into account.

The closest in technical essence to the proposed method is a method for developing a lithologically shielded oil-saturated lens with one well, which includes alternating the selection of reservoir fluid to reduce reservoir pressure to a level of oil saturation with gas or a drop in oil production to an extremely cost-effective and water injection with an increase in reservoir pressure. In the method, the lens profile is analyzed, the boundaries and areas with a lower and increased location of the reservoir are determined, at least one horizontal well is drilled through a vertical well into the low or high section in the direction of the low or high section, water is pumped periodically into the low section of the lens, and formation fluid is selected periodically from an elevated portion of the lens (RF patent No. 2242594, IPC EV 43/20, publ. 12/20/2004).

The known method allows to increase oil recovery by drilling an additional horizontal wellbore, however, here also does not take into account the change in the properties of the reservoir during development. For small oil lenses, horizontal borehole drilling is an economically costly undertaking and does not always lead to a positive economic effect.

An object of the invention is to increase oil recovery of the reservoir by changing the modes of selection-injection.

The technical problem is solved by the method of developing small individual oil lenses, including opening the lens with a single well, alternating the selection of reservoir fluid from the upper part of the lens to reduce the reservoir pressure to the level of oil saturation with gas or drop the oil flow rate to the most cost-effective and inject the displacing agent with increasing reservoir pressure.

It is new that injection of the displacing agent is carried out at a pressure not exceeding the rock fracture pressure, determined by the geological and physical parameters of the lens, until the injectivity is reduced to 50% of the initial one, and the liquid is taken until the oil production rate drops by 20-60% from the initial moreover, the periods of injection at the initial stage are carried out at regular intervals until the reservoir pressure reaches the initial pressure, and the periods of injection at the initial stage are also carried out at regular intervals until the reservoir pressure is reduced to 80-90% of the saturation pressure, the initial development phase is considered completed at lower initial oil production rate in the second and subsequent cycles of selection to 30-60% of the original oil flow in the first cycle.

The experience of developing both terrigenous and carbonate reservoirs shows that when reservoir pressure is reduced to 80-90% (depending on geological and physical characteristics: 90% for fractured-pore reservoirs, 80% for pore reservoirs), the gas pressure from oil is not allocated, but is allocated when this value is exceeded.

The injection of the displacing agent in each cycle is carried out until the injection rate is reduced to 50% of the initial one, because the calculations showed that further continuation of the injection with decreasing injectivity is impractical, and during this time the reservoir pressure manages to rise above the initial one.

The selection of fluid in each cycle is carried out until the oil production rate drops to 20-60% of the initial one. These values are determined from economic considerations associated with a minimum cost-effective oil production. Calculations for various geological and physical characteristics of the reservoir showed that the economic profitability of the well remains at the current oil flow rate of 20-60% of the original.

The initial stage of development is considered completed when the initial oil production rate in the second and subsequent extraction cycles is reduced to 30-60% of the initial oil production rate in the first cycle. Calculations of various options for the duration of the initial stage of development showed that when the initial oil production rate decreases by less than 30% in the subsequent ones after the first cycle and further transfer to the regime proposed in the invention, losses of total oil production occur, because much more water is taken at the initial stage than oil. And with a decrease in the initial oil production rate of more than 60%, the total oil recovery also turns out to be lower, and a larger number of subsequent cycles is required.

Figure 1 presents a diagram of the selection of products from the lens. Figure 2 shows the injection scheme of the displacing agent. Figure 3 is a graph of the cumulative oil production by the prototype method and the proposed method. In Fig.4 is a graph of oil production by the prototype method and the proposed method. Figure 5 is a graph of reservoir pressure (prototype and the proposed method).

The method is implemented as follows.

On the oil reservoir 1 (Fig. 1), lithologically shielded by impermeable rocks 2, one well is drilled, equipped, a second opening is performed at the roof 3 and at the bottom 4. Install the packer 5 between the tubing 6 (tubing), which is pumped , and production casing 7. Through the upper perforation holes 8 along the tubing 9, the production of the well is selected (Fig. 1) until the reservoir pressure is reduced to 0.8-0.9 from the pressure of oil saturation with gas. Then transfer this well to the injection of produced water (figure 2) through the tubing 6 through the lower perforations 10, until the reservoir pressure reaches the initial one. Then again produce the selection of products. Loops repeat.

Gradually, with each cycle, the initial and final oil production rates decrease. Without waiting for the reservoir pressure to decrease to 0.8-0.9 from the saturation pressure, the well is transferred under injection, and at an oil production rate of 30-60% of the initial in the first cycle. The injection is carried out at a maximum pressure, but not exceeding the hydraulic fracturing pressure, to a decrease in injectivity to 50% of the initial one, after which the well is transferred to production. The liquid is taken until the oil production rate drops to 20-60% of the initial in the current cycle. The cycles are repeated until the water production of the well reaches 98% or a minimum profitable oil production.

An example of a specific implementation of the method.

Productive strata of the field are represented by pore-fissure carbonate deposits, the depth of the roof is 710 m.

Select lithologically shielded by impermeable rocks 2 (figure 1) reservoir 1 of small size - 250 × 250 m, purely oil saturated. Formation thickness 5-30 m, matrix porosity 0.15, fracture porosity 0.01, matrix permeability 50 mD, fracture permeability 500 mD, initial reservoir temperature 25 ° C, initial reservoir pressure 10 MPa, saturation pressure oil gas - 3.1 MPa, the viscosity of oil in reservoir conditions - 27 MPa · s, the viscosity of water in reservoir conditions - 1.69 MPa · s.

Carry out the construction and preparation for operation of a vertical well. A secondary opening of the productive part of deposit 1 (Fig. 1) is carried out at the roof 3 and at the sole 4. Install a packer 5 between the tubing 6 (intended for water injection) and production casing 7 and between the openings 8 and 10, counting from the formation roof in proportion 3 : 2.

Through the upper perforation holes 8, a well production is selected with an initial oil production rate of 10 tons / day (Fig. 4) using tubing 9 at a bottomhole pressure of 3.5 MPa for 4 years, until the reservoir pressure drops to 0.9 from the oil saturation pressure gas (figure 1), i.e. up to 2.8 MPa (figure 5). Then, this well is transferred to the injection of produced water with an injection rate of 40 m ³ / day via tubing 6 through the lower perforation holes 10 under an injection pressure of 16 MPa for 1 year until the reservoir pressure reaches its initial value (Fig. 2). Then again, the production of wells is selected for tubing 9 with the same conditions as in the first cycle. The cycles are repeated with a production period of 4 years, injection - 1 year.

Gradually, with each cycle, the initial and final oil production rates decrease. By the end of the third production cycle, without waiting for the reservoir pressure to decrease to 0.9 from the saturation pressure, the well is transferred under injection. The oil production rate by this time is 1.8 t / day, i.e. 30% of the initial 6 t / day (in this cycle). The injection is carried out under a pressure of 20 MPa, i.e. not exceeding the fracture pressure of the rock, to a decrease in injectivity of 20 m ³ / day, i.e. 50% of the original, after which the well is transferred under production. The selection and injection cycles are repeated with the condition that the oil production rate is 30% of the initial in this cycle, and the injection is until the injectivity is reduced to 50% of the original.

The cycles are repeated until the water production of the well reaches 98% or the minimum profitable oil production, in this case 0.7 t / day.

A total of 7 cycles were conducted. By the end of the development of the proposed method, 29.9 thousand tons of oil was produced (Fig. 3), the oil recovery coefficient (CIN) was 0.305. According to the prototype method, 7 cycles were also conducted, cumulative oil production amounted to 25.2 thousand tons and a recovery factor of 0.257. Thus, the CIN increase was 0.048, or 18.6%.

By changing the modes of selection and injection at a late stage of development, the proposed method allows to increase the oil recovery factor and, as a result, oil production by 15-20%.

Claims (1)

The method of developing small individual oil lenses, including opening a lens with a single well, alternating the selection of formation fluid from the upper part of the lens to reduce reservoir pressure to a level of oil saturation with gas or drop in oil flow rate to an extremely cost-effective and injecting displacing agent with increasing reservoir pressure, characterized in that the injection of the displacing agent is carried out at a pressure not exceeding the rock fracture pressure, determined by the geological and physical parameters of the lens, until the injectivity decreases to 50% of the initial one, and the fluid is taken until the oil production rate drops by 20-60% of the initial one, and the pumping periods at the initial stage are carried out at regular intervals until the reservoir pressure reaches the initial one, and the sampling periods at the initial stage are also carried out through equal time intervals until the reservoir pressure drops to 80-90% of the saturation pressure, and the initial stage of development is considered completed when the initial oil production rate in the second and subsequent extraction cycles is reduced to 30-60% of the per initial oil production in the first cycle.

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