RU2126883C1 - Method for development of natural gas deposits with non-uniform reservoirs - Google Patents

Abstract

FIELD: oil and gas production industry. SUBSTANCE: according to method, drilled are vertical and/or horizontal producing wells. Productive beds are opened. Recovered from producing wells is gas and accompanying water. In development of deposits in macro non-uniform beds, accompanying brine water is injected into low-permeable and/or low-draining zones of same bed is developed. Amount of water is injected is not larger than gas-saturated volume of porous space in low-permeable and/or low-draining zone. EFFECT: higher gas recovery due to activation of filtration processes and involving low-draining gas reserves into development. 2 dwg, 4 tbl

Description

 The present invention relates to the field of oil and gas industry, in particular to the field of development of gas and gas condensate fields with productive formations that are sharply heterogeneous in reservoir properties.

 A known method for the development of floating gas fields, including drilling systems of vertical or horizontal wells, gas production in the mode of depletion of reservoir energy and operation of wells at critical anhydrous gas rates (see Lapuk B. B., Brudno A. L., Somov B.E. About bottom water cones in gas deposits. Gas industry, 2, 1961). A disadvantage of the known technical solution is the need to limit the production capacity of wells from above, which leads to an increase in the required number of wells for field development and, as studies show, to lower gas recovery.

 Closest to the proposed one is a method of developing gas fields under the regime of depletion of reservoir energy and operating wells for given water-gas (gas-water) factors (see Zakirov S.N. Development of gas, gas condensate and oil and gas condensate fields, Vneshtorgizdat, p. 560, 1998). The disadvantage of this development method is the relatively low gas recovery, as well as the presence of a problem of disposal of produced produced water. In the case of watering wells, current practice provides for the injection of produced formation water into a specially selected aquifer. Obviously, in this case, there is pollution of the aquifer that is not involved in the development process. In addition, significant costs are required for appropriate exploration work for a future landfill for produced water, as well as the costs of drilling special injection wells. Usually, deep-lying aquifers with low permeability are used as suitable objects, which predetermines significant costs for drilling expensive wells. Currently, the injection of produced water into the same developed reservoir is not practiced due to the fear of lowering the gas recovery of the reservoir as a result of pinching of micro- and macro-volumes of gas injected into the reservoir by water.

 The problem of gas recovery is even more significant in the case of the development of gas fields with macro-heterogeneous reservoir properties, as evidenced by the experience of developing real gas fields. This is due to the fact that only the operating mode of production wells does not manage to effectively influence the filtration processes, especially on the displacement processes in such productive formations.

 The basis of the present invention is the creation of a method of developing natural gas fields, which provides increased gas recovery due to the active impact on the filtration processes in macro-heterogeneous formations to engage in the development of weakly drained gas reserves with the simultaneous disposal of produced produced water.

The achievement of the task is achieved by the fact that in the method of developing a gas deposit, including drilling vertical and / or horizontal wells, opening a reservoir and selecting from production wells gas and associated formation water, according to the invention, they are injected into low-permeable and / or weakly drained zones of the developed formation along the way selected formation water in a volume not exceeding the gas-saturated volume of the pore space of the low permeability and / or poorly drained zone, as well as the fact that:
- injection of produced formation water is carried out from the moment of flooding of production wells;
- simultaneously with the selection of gas, the associated formation water is injected from the overlying or underlying horizons of the reservoir;
- for injection of produced formation water, exploratory and / or production wells with additionally drilled horizontal lateral shafts and additionally drilled single-hole and / or multi-lateral horizontal wells are used.

 The method is as follows.

 Drill gas (gas condensate) deposits by a system of vertical and / or horizontal wells. With their help, gas production begins due to the natural reservoir energy of compressed gas.

 In the process of development: a) watering of a number of production wells with contour or bottom water begins, usually associated with zones with high reservoir properties, b) formation zones with deteriorated reservoir properties are identified, which is manifested in low production rate of production wells.

 All water entering the wells is extracted and extracted to the surface, and then pumped back into the same developed reservoir. Water is injected into reservoir zones with poor reservoir properties or poorly drained, for example, peripheral, reservoir zones. To implement the injection plan, low-rate gas wells are transferred to the category of injection water wells.

When water is pumped into low-permeable, poorly drained zones (parts) of the formation, the injected water does a positive job - it displaces gas from the low-permeability zone to the highly permeable one. Each water injected into the reservoir m ³ displaces P m ^{3 of} gas, where P is the number of reservoir pressure atmospheres in the area of the injection well at the time of the start of water injection. Produced from the developed horizon and injected into the same horizon, produced water, of course, is compatible with the contour or bottom water entering the reservoir, which does not require significant costs for the preparation of water before pumping it into the reservoir.

 Obviously, gas flooding results in gas losses due to pinching of individual gas microbubbles. But the jamming of macro-volumes of gas is eliminated (partially or completely), which is observed, for example, during the creation and operation of underground gas storages in aquifers (see Derkach MI and other Features of the creation and operation of underground storages in the western region of Ukraine. Proceedings of the International conferences on underground gas storage, Moscow, September 11-15, 1995, p. 95). As a result, the volume of active gas decreases and the volumes of buffer gas increase.

 It is easy to see that the total volumes of water injected into the reservoir should have a top restriction. Indeed, if the entire pore volume of the reservoir is taken as the upper limit, then unreasonably large gas losses can occur in highly permeable reservoirs. Therefore, the gas-saturated pore volume of the formation zones that are weakly involved in drainage is taken as a top restriction. In other words, the total volume of water produced in passing to the produced water must not exceed the gas-saturated pore volume of zones with inactive gas reserves, which are difficult to extract using traditional methods.

 In the proposed technology, exploratory wells that are not quite suitable for gas production can also be used as injection wells.

 Due to the need to pump water into the low-permeability zones of the reservoir, sidetracks are drilled in production wells, which are transferred to the category of injection wells. In some cases, special horizontal or multilateral wells are drilled. Low well flow rates may be due to low reservoir properties of the formation and low allowable depression on the formation. When water is injected, repression on the formation can be, generally speaking, arbitrarily large, which positively affects the injectivity of the wells.

 The process of injecting formation water into low-permeable, slightly drained zones of the formation can be carried out from the very beginning of the development process. This is done, for example, in the case of a multi-layer field, when there is flooding of wells of other horizons and there is a problem of utilization of produced water.

 As a result of the implementation of water injection precisely into the developed gas-bearing horizon, two problems are simultaneously positively resolved: 1) environmental, associated with the burial of produced produced water and 2) technological and economic, which consists in increasing the gas recovery of a macro-heterogeneous reservoir by reservoir properties.

 In the future, the invention is illustrated by a description of a variant of its implementation, illustrating the principle of transformation of a negative factor (watering wells) into a positive result - an increase in gas recovery of macro-heterogeneous productive formations and utilization of produced water.

 Gas-hydrodynamic calculations in order to justify the effectiveness of the proposed approach are performed in relation to typical parameters of gas deposits in Western Siberia.

 Example.

 As an object of development, a floating gas reservoir with parameters characteristic of a number of deposits in the Cenomanian deposits (Western Siberia) is considered. It is known that due to the formation of specific volumes of drainage, the study of the development technologies under consideration can be carried out on the reservoir element.

 In FIG. 1 shows a top view of a zone-heterogeneous reservoir properties of the reservoir. It consists of two zones. The right high-permeability zone is characterized by a permeability coefficient of 0.5 darsi, and the left, low-permeability zone, is two orders of magnitude smaller, that is, 5 mdarsi. These heterogeneity zones can be traced both in the gas and in the aquifer of the formation.

 The low permeability zone is drained by two wells, and the high permeability zone is drained by one well. In FIG. 1 also gives a grid approximation of the considered element of the formation in the XOY plane. In the centers of condensing unit cells, these wells are also located.

 In FIG. Figure 2 shows a profile section of a development element along the axis of the wells and its grid approximation in the YOZ plane. In the most condensed grid elements there are three vertical, imperfect in the degree of opening of the well. The aquifer in the plan is assumed to be infinite in length. Other initial data are presented in table. 1.

 In relation to the considered element of the reservoir, three options for its development are being investigated. Typical of these options is that the total number of wells remains unchanged and the forecast development period is limited to 30 years. Gas-hydrodynamic calculations are performed using a three-dimensional two-phase (gas-water) mathematical model with the same grid approximations of the development element and the aquifer.

Option I. Here, the development technology is implemented during the operation of production wells at specified gas rates with the transition to critical anhydrous gas rates. For a critical anhydrous flow rate is taken when the gas-water factor equal to 10 ⁵ m ³ / m ³ , i.e. when 10 ⁵ m ³ of gas extracted 1 m ³ of water. The gas production rate of a highly productive well is 200 thousand m ³ / day, and low-productive wells - 10 thousand m ³ / day. The end of development occurs after reaching 30 years or with a decrease in gas production (due to the transition to anhydrous production) to an unprofitable level (5 thousand m ³ / day).

Option II. In this embodiment, controlled watering of wells is allowed. This means that in the process of developing a formation element from the moment formation water appears in the wells, they begin to be operated at a given permissible value of the gas-water factor (2 • 10 ³ m ³ / m ³ ). Until then, all three wells have been operating at constant gas rates. The production rates of two low-rate wells, as in option 1, are 10 thousand m ³ / day, and high-production ones - 200 thousand m ³ / day.

Option III. This option explores the proposed development technology. As in option II, the well in the highly permeable zone of the formation is operated with a constant flow rate of 200 thousand m ³ / day and a predetermined gas-water factor (2 • 10 ³ m ³ / m ³ ) from the moment the formation water enters the well. Wells in the low-permeability zone do not produce gas, and from the very beginning they are transferred to the discharge category. At the same time, water is pumped into each of them at a rate of 500 m ³ / day.

 The results of predictive calculations for the considered options are presented in table. 2-4. Analysis of the calculation results allows us to note the following.

 The worst development indicators are characterized by option I. With the accepted, identical for all options, initial data and limitations, only 26.55% of the initial gas reserves are extracted from the reservoir by the end of the year 30. This is due to the fact that a highly productive well is eliminated from the production fund in the eighth year of development due to cone formation of bottom water. Although low-production wells have been operating for 30 years, they cannot seriously affect the final gas recovery.

In option II, the situation with gas recovery improves significantly and by the end of the year 30 it reaches 43.5%. This is due to the fact that the possibility of controlled associated production of water is allowed. As a result of this, the period of operation of a high-yield well increases to 15 years, which predetermines the indicated increase in gas recovery. However, in this option, the problem of utilization of 108.3 thousand m ^{3 of} produced water is not solved.

According to option III, which reflects the proposed development technology, gas recovery at the end of 30 years reaches 55.3%, i.e. is the largest compared to options I and II. Compared with option I, gas recovery in option III increases by 28.75 points or 108.3%, and compared with option II by 11.8 points or 27.1%. An additional increase in gas recovery in option III compared to option II occurred only because of the attempted injection of water into the reservoir. In option III, for this reason, there is also no problem inherent in option II of utilizing associated produced water, because in option III, the volumes of injected water even exceed the incidentally produced volume of water in an amount of 165.2 thousand m ³ .

 Thus, the above research results confirm the validity of the proposed approach to the development of gas deposits with reservoirs that are heterogeneous in reservoir properties.

Claims (1)

 A method of developing natural gas fields with reservoir formations that are heterogeneous in reservoir properties, including drilling vertical and / or horizontal production wells, opening productive formations and selecting gas and associated water from production wells, characterized in that, while developing fields in macro-heterogeneous formations, produced reservoir water is collected pumped into low-permeable and / or weakly drained zones of the same developed formation and in a volume not exceeding the gas-saturated volume the orthic space of a low permeable and / or poorly drained zone.

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