RU2109930C1 - Method for development of gas deposits in continental shelf - Google Patents

Abstract

FIELD: oil and gas production industry. SUBSTANCE: this relates to development of gas, gas-condensate, oil, and gas-oil deposits in continental shelf. According to method, undertaken are operations of drilling bore-holes, opening of gas-saturated reservoirs, and recovery of gas from wells in mode of exhausting bed energy. Method is aimed at avoiding construction of booster compressor station and subsequent compression of gas for its further transportation, and also at reducing cost of developing deposit to commercial level. Starting from calculated moment of time, brought into operation are injection wells for maintaining bed pressure with pumpless injection of sea water into injection wells due to water column between sea water level and well head level. Aforesaid development procedure allows for reduction of capital investments in developing gas deposit in continental shelf due to delivery of gas into trunk gas pipeline without using compressors and maintaining gas bed pressure without pumping. EFFECT: higher efficiency.

Description

 The invention relates to the oil and gas industry, and in particular to the field of development of gas fields on the continental shelf.

 There is a method of developing gas fields, including drilling a system of vertical or horizontal wells, gas production in the mode of depletion of reservoir energy and the subsequent commissioning of a booster compressor station (DCS) to supply gas to the inlet of the main gas pipeline with the pressure required for long-distance transport [1].

 A disadvantage of the known technical solution is the need to build an expensive compressor station and significant energy costs for gas compression before it is fed into the main gas pipeline. Particular difficulties with gas compression arise in the development of gas fields on the continental shelf, when the costs of constructing a BC are supplemented by the associated costs of building expensive platforms, especially at great depths of the sea.

 There is also known a method of developing gas and gas condensate deposits based on in-situ flooding in the presence of a cross-section, a separator with reduced filtration and capacitive properties with respect to the host deposits [2].

 The disadvantage of this method is the limited application, due to the extremely rare possibility of the presence of the alleged geological features of the structure of the gas deposits. The use of such a development method in offshore fields is also difficult due to the significant costs for the construction of a pumping station, distribution pipelines and the associated costs for the construction of an offshore platform.

 The basis of the invention is the creation of a method of developing gas fields, which simplifies the process of developing deposits on the continental shelf by implementing a pump-free mode of maintaining reservoir pressure and an uncompressed mode of supplying fluid and transportation in the main pipeline, which results in a reduction in the cost of developing fields.

 The problem is achieved in that in the method for developing a hydrocarbon-containing continental shelf deposit, including drilling wells, opening production intervals and selecting fluid from production wells in the mode of depletion of reservoir energy with subsequent maintenance of reservoir pressure through injection wells, according to the invention, the formation pressure is maintained by a natural column head seawater pumped into injection wells, wellhead pressure in which corresponds to pressure Yew on the depth of the sea in their places of accommodation.

 The basis of the invention is the efficient use of the natural factor - the natural column of sea water, which ensures the maintenance of reservoir pressure in the reservoir and gas supply to the main pipeline without the use of pumps and compressors.

 The invention is further illustrated by the description of a specific embodiment, illustrating the principle of using a natural column of sea water.

 Evaluation calculations of the effectiveness of the proposed approach have been performed for a single gas deposit on the continental shelf.

 The method is as follows.

 Drilling a gas deposit on the continental shelf with a system of vertical or (and) horizontal wells. With their help, gas production begins due to the natural reservoir energy of compressed gas.

 The process of developing a gas deposit is monitored. After 1, 2, 3, etc. years of development, the inverse problems are solved (in three-dimensional, two-phase formulation) to clarify the reservoir properties of the formation in the gas reservoir-water basin system based on actual gas production data for 1, 2, 3, etc. years of operation.

 With specified gas reserves, gas reservoir and water basin parameters, predictive calculations are carried out. These predictive calculations reveal the degree of possible participation of the natural water pressure regime in the reservoir pressure replenishment, i.e., it substantiates the possibility of installing the required number of injection wells with wellhead pressures corresponding to the depths of the sea at their locations, and also calculates the dynamics of their commissioning in such a way that maintained pressure in the reservoir eliminated the need for gas compression to supply it to the main gas pipeline.

 To implement this effect, the required number of injection wells is constructed with a filter device at the mouth. In the required sequence, they begin to take sea water. At the same time, the wellhead pressure necessary for the required injectivity is created due to the available “free” column of sea water (from sea level to the mouth of the injection well).

 According to forecast calculations, a plan to maintain reservoir pressure at the required level is being implemented. To do this, the planned injection wells are put into operation in sequence. At the same time, wellhead equipment includes a remotely controlled valve and filter equipment that prevents the entry of marine fauna and flora into the well. A water meter and a hydraulic turbine are installed in the injection well. The hydraulic generator generates electricity for the needs of the platform and the wellhead gate actuator. This energy can also be used for the needs of more thorough treatment or heating of seawater pumped into the reservoir.

 Ongoing monitoring of the development of the field may lead to a refinement of the projected development indicators, since they were at an early stage of the reservoir exploitation. Then there is no difficulty, for example, with disconnecting any well from the designed pressure maintenance system.

 Traditionally, an increase in the depths of the sea is a negative factor in the development of shelf deposits. The effectiveness of the proposed technology, on the contrary, increases with increasing depths of the sea and partially smoothes out the negative in the first part, because an increase in the depth of the sea is accompanied by an increase in "free" pressure at the mouths of injection wells.

 In the case of an oil reservoir, sea water injection is carried out almost from the very beginning of development. To increase the injectivity of injection wells and reduce their number, it is possible to consider the development of an oil reservoir at a pressure slightly lower than the initial reservoir pressure.

 In the case of gas condensate deposits, the optimal time for the start of water flooding and the level of maintained pressure are determined on the basis of gas-hydrodynamic and technical and economic studies and calculations.

 An example implementation of the proposed method.

 Deposit I of the shelf gas field A is characterized by an initial reservoir pressure of 19.9 MPa. When developing it in the mode of depletion of reservoir energy for 25 years, it is necessary to either commission the first stage of the booster compressor station (BCS), or switch to a declining gas production, since the pressure at the wellheads reaches 7.5 MPa. A decrease in pressure below this value will not allow gas to be transported in the required volumes.

 The traditional technology of development is associated with significant costs for the construction of BCS, taking into account the associated costs of the platform and annual operating costs. In this case, the final gas recovery coefficient will be equal to 76%, due to the sufficiently high casting pressure.

 The proposed development option will require drilling 22 injection wells. Required investment will decrease by about 6 times at almost zero operating costs (due to the very essence of the proposed technology). In this case, the final gas recovery coefficient will be equal to about 74%, i.e. commensurate with the traditional development option. In addition, the technology under consideration allows us to extend the period of constant gas production by 5 years with the corresponding economic effect.

 As a result, the pressure in the reservoir is maintained that provides a compressor-free gas supply at the intake of the main gas pipeline. The consequence of this is a reduction in investment and operating costs for the development of a gas field on the continental shelf. The absence of compressor and pumping equipment eliminates the entry into the atmosphere of gas combustion products in the respective drives. In addition, the installation of hydraulic turbines in injection wells makes it possible to obtain cheap electricity for local consumption.

 Thus, the proposed technology in its final indicators of gas production is preferable in comparison with traditional approaches to the development of offshore gas deposits.

Claims (1)

 A method of developing gas fields on the continental shelf, including drilling wells, opening production intervals and selecting fluid from production wells in the mode of depletion of reservoir energy, followed by maintaining reservoir pressure through injection wells, characterized in that the reservoir pressure is maintained by the natural pressure of a column of sea water pumped into injection wells, the wellhead pressure in which corresponds to the pressure at a depth of the sea at their locations.