RU2602621C1 - Gas hydrate deposits development method - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention relates to development of gas hydrate hydrocarbon deposits. Method is as follows: main well is drilled with opening pay and underlying water-bearing reservoir, drilled well is perforated in the pay and underlying water-bearing bed zone. Then, tubing strings with submersible pump unit are lowered to the main well and gas-liquid mixture is extracted at the border of gas-water contact of the pay with simultaneous separating gas-liquid mixture in the well. Gas is extracted through annular space, liquid with dissolved gas is extracted through tubing strings. This liquid is pumped into the underlying water-bearing bed by means of the said submersible pump unit. At that, at least two bypass wells are additionally drilled along the periphery of the deposit with opening the underlying water-bearing bed. They are perforated in the pay and underlying water-bearing bed zone. During extracting gas-liquid mixture thermal reservoir mineralized water is bypassed from the underlying water-bearing bed in the overlying pay for thermal hydrate dissociation to ensure circulating thermal reservoir water and hydrate dissociation water between the pay and underlying water-bearing bed without lifting water to the surface. During extracting gas-liquid mixture pressure is decreased in the bottom-hole zone of gas hydrate bed to a value, providing the beginning of hydrate dissociation.

EFFECT: technical result is increased efficiency of the method due to increased gas extraction, increased period for hydrates-free operation of wells and reduced power consumption.

1 cl, 1 ex, 1 dwg

Description

The invention relates to the field of development of gas hydrate hydrocarbon deposits.

A known method of developing a gas hydrate deposit, including drilling bypass and production wells in the rock, followed by production of gas through the bypass wells while maintaining pressure in the developed reservoir by transferring the thermal formation water from the underlying horizon to the overlying one, while the bypass well is drilled to the formation with thermal waters, underlying relative to the gas hydrate reservoir, perform a horizontal branch under the sole of the gas hydrate reservoir to supply formation water and drill of flue hole with vertical outlet to the surface (RU 2250365, 2003 YG).

The disadvantages of the method include a large accumulation of water in the bottomhole zone, which will reduce the phase permeability for gas, as well as the pressure drop in the reservoir with thermal waters will not allow to develop a gas hydrate reservoir in this way for a long time.

Of the known technical solutions, the closest to the proposed technical essence is a method of developing a gas hydrate field, which includes drilling a well with opening a productive formation and an underlying aquifer, then tubing with a submersible pump unit is lowered into the well and a gas-liquid mixture is selected at the gas-water boundary the contact of the reservoir with the simultaneous separation of the gas-liquid mixture in the well, gas is produced by annulus of the space well, and the fluid with dissolved gas - of the tubing which with the above submersible pump unit is pumped into the underlying aquifer (RU 2438009, 2010 YG).

The disadvantages of the method include the inevitable decrease in temperature at the bottom of the well due to both dissociation of hydrates occurring with the absorption of a large amount of heat and the process of gas throttling in the bottomhole formation zone, which additionally leads to a decrease in temperature. Lowering the temperature in the bottomhole zone leads to the formation of secondary hydrates, while the front of the secondary hydrates begins to form from the bottom of the well. Both of these factors lead to a gradual decrease in the flow rate of a gas well until the cessation of gas production from the well. The decrease in water saturation in the area located below the bottom of the gas hydrate formation does not completely solve this problem, because upon decomposition of 1 m ^{3 of} hydrate, 0.784 m ^{3 of} water is formed and the possibility of the formation of secondary hydrates is not excluded. The disadvantages also include the low injectivity of the aquifer, from which nothing is taken, and the lack of injectivity after a short period of time. The described development method may take a short time and may not justify the cost of a submersible pump installation.

The objective of the invention is to provide a method for the development of gas hydrate deposits, providing an increase in gas production and extending the life of non-hydrate wells, as well as reducing energy costs.

This object is achieved by the fact that in the method of developing a gas hydrate deposit, the main well is drilled with the productive formation and the underlying aquifer being opened, the perforated hole is drilled in the zone of the productive reservoir and the underlying aquifer, then tubing with a submersible is lowered into the main well pumping unit and select gas-liquid mixture at the boundary of the gas-water contact of the reservoir with the simultaneous separation of gas-liquid mixture in the well, and gas production is carried out in the annulus, and liquid with dissolved gas through tubing, which is pumped into the underlying aquifer using the aforementioned submersible pump installation, according to the invention, at least two bypass wells are additionally drilled on the periphery of the deposit with the opening of the underlying aquifer and carry out their perforation in the zone of the reservoir and the aquifer, in the process of selecting a gas-liquid mixture they allow the transfer of thermal formation mineralized water from the underlying aquifer to the overlying productive reservoir for thermal dissociation of the hydrate, ensuring the circulation of the thermal reservoir water and the water of hydrate dissociation between the reservoir and the underlying aquifer without raising water to the surface, while the gas-liquid mixture is reduced during the selection process pressure in the bottom-hole zone of the gas hydrate formation to a value that ensures the onset of hydrate dissociation.

The technical result achieved is achieved by ensuring the circulation of thermal formation water between the aquifer and the reservoir and by eliminating the rise of formation water to the surface.

The invention is illustrated in the drawing, which shows a schematic diagram of an installation for implementing the proposed method.

The following notation is adopted in the drawing: 1 - well, 2 - aquifer, 3 - perforation hole, 4 - tubing, 5 - pump unit, 6 - submersible motor, 7 - dynamic level, 8 - packer, 9 - control station 10 - downhole cable, 11 - surface cable, 12 - transformer, 13 - partial transducer, 14 - loop, 15 - reservoir, 16 - overflow well.

The method is as follows.

Drilling a well 1 with opening the underlying aquifer 2.

In the drilled well 1, perforation 3 is carried out in the zone of the aquifer 2 and in the zone of the reservoir 15. On the tubing 4 lower the pump unit 5 with a submersible motor 6 below the dynamic level 7. Install the packer 8 between the reservoir 15 and the aquifer 2. The connection of the submersible motor 6 with the control station 9 is carried out using the downhole cable 10 and the surface cable 11. The operation of the submersible motor 6 is controlled using a transformer 12 and often deleterious converter 13.

By means of a pumping unit 5, a gas-liquid mixture is selected. As a result of the selection of the gas-liquid mixture, the reservoir pressure in the bottom-hole zone of the gas hydrate formation 15 decreases, the hydrate dissociation process begins.

The separation of the gas-liquid mixture takes place in the well 1 and is carried out by means of a gas separator, which is part of the submersible pump unit 5. Next, the gas through the annulus of the well enters the surface in the loop 14 and then to the gas treatment unit and to the consumer, and the water after separation of the gas-liquid mixture using the submersible pumping unit 5 is pumped into the underlying aquifer 2.

In addition, bypass wells 16 are drilled around the periphery of the reservoir to the formation 2 with thermal waters, lying relative to the gas hydrate reservoir, to maintain pressure in the developed reservoir and to ensure the injectivity of the aquifer by transferring the thermal reservoir water from the underlying horizon to the overlying one. Thus, circulation of produced water and hydrate dissociation water is carried out.

The proposed method provides the decomposition of gas hydrates not only by reducing pressure at the bottom of the well during the selection of the gas-liquid mixture, but also by the thermal and inhibitory effects of thermal waters.

The following is an example of a specific implementation of the proposed method.

An example is presented for the operation of the wells of the Messoyakha gas hydrate field. Let us determine the equilibrium thermobaric conditions for the existence of hydrates of the Messoyakhskoye field. The gas composition of the Messoyakhskoye field is mainly represented by methane ((98-99 vol.%). Therefore, for further calculations, we can assume that the conditions for dissociation of hydrates of the Messoyakhskoye field correspond to the conditions for the dissociation of pure methane and make up 6.8 at a reservoir temperature of 10.5 ° C. MPa Therefore, at pressures below 6.8 MPa, the dissociation of existing hydrates occurs.

The initial reservoir pressure and temperature of the Messoyakhskoye field are 7.5 MPa and 10.5 ° C, respectively. To begin the dissociation of hydrates, it is necessary to reduce the pressure in the sole of the gas hydrate region of the field by 0.7 MPa.

The reservoir properties of the reservoir are as follows - permeability k = 93.1 mD; porosity m = 25%. Assuming that the reservoir and filtration parameters in the aquifer remain the same, it is possible to calculate the formation water at which pressure will begin to decrease in the reservoir area located below the gas hydrates.

In accordance with the proposed technology, a well 1 is drilled with an underlying insulated aquifer 2 opened. In addition, two bypass wells 16 are drilled in the rock up to the thermal water layer 2 below the gas hydrate deposit at the periphery of the deposit. Production wells of the Messoyakhskoye field have the following design:

- conductor - 219 mm - to a depth of 450.0-500.0 m;

- production casing - 146 mm - to a depth of 870.0-900.0 m, i.e. almost to the bottom;

- lift column - tubing d = 73 mm.

A pumping unit 5 with a submersible electric motor 6 is installed. The most suitable standard installation size of a submersible centrifugal pump for the considered example is UETSN5A-360-600.

The well productivity coefficient under the accepted assumptions will be - 50.18 t / (day · MPa) (the calculation was made for the following conditions - formation water density - 1043 kg / m ³ ; thickness of the formation 10 m; radius of the supply circuit - 300 m; reduced well radius - 0.2 m; formation water viscosity - 1.08 MPa · s). The production fluid rate calculated by the Dupuis formula is 351.26 t / day.

The diameter of the production tubing is capable of providing a calculated fluid rate.

The packer 8 is installed between the reservoir and the aquifer 2. When injecting the reservoir fluid into the reservoir, the following arrangement of underground equipment is carried out: production packer type 2 PD-YAG-118-500 with an outer diameter of 118 mm, for wells with production string 139.7 mm in diameter - the packer type APD-YAG-112-500.

The connection of the submersible motor 6 with the control station 9 is carried out using the downhole cable 10 and the surface cable 11. The operation of the submersible motor is controlled using a transformer 12 and a frequency converter 13.

As a result of the pump and the selection of the gas-liquid mixture, the reservoir pressure in the sole of the gas hydrate formation is reduced.

The calculation results show that the reservoir pressure in the drainage area is up to 50 meters below the pressure of the onset of hydrate dissociation.

At the same time, as a result of water withdrawal, water saturation decreases in the zone located below the bottom of the gas hydrate formation.

The separation of the gas-liquid mixture occurs in the well 1. Next, the gas through the annulus enters the surface in the loop 14, where it is prepared, and water is pumped into the underlying aquifer 2.

Upon dissociation of hydrates, 160 m ^{3 of} gas and 1 m ^{3 of} water are formed. For the considered well design, when the water enters, the dynamic level changes by 59 meters for each cubic meter of water entering the well. When the water reaches a certain level, the wells self-pressurize with produced water and the wells are decommissioned. The performance of the selected pump allows you to constantly remove water from the well and maintain pressure in the bottomhole formation zone, which ensures hydrate dissociation. Under these conditions, gas will enter the well continuously without the risk of secondary hydrate formation until the gas saturation in the formation is 5-10%, when the phase permeability for gas is zero. The total gas withdrawal from the gas hydrate reservoir will be 90-95%.

Along the periphery of the formation, by-pass wells, thermal formation water with a high degree of mineralization, which has a heat capacity significantly exceeding the heat capacity of fresh water, enters the reservoir.

The flow rate of thermal formation water required for processing 1 m ^{3 of} rock is taken:

where: q is the rate of thermal formation water,

With _p - the heat capacity of the rock, kcal / m ³ · ° C;

C _T - heat capacity of thermal formation water, kcal / m ³ · ° C

ΔT _f = T _f -T _pl , ° C;

ΔT = T ₀ -T _pl , ° C;

T ₀ - temperature of thermal formation water, ° C;

T _PL - reservoir temperature, ° C;

T _f - phase transition temperature, ° C;

m is the porosity;

ΔH is the heat of the phase transition of gas hydrate, kcal / m ³ ;

α _guide - hydration coefficient.

The heat capacity of the rock is C _p = 600 kcal / m ³ · ° C; m = 0.2; ΔH = 1.25 kcal / m ³ ; α _guide = 0.4; T ₀ = 60 ° C; T _pl = 3 ° C; t T _f = 7 ° C thermal capacity of thermal formation water C _T = 1000 kcal / m ³ · ° C, respectively

those. for the implementation of the method according to the invention, approximately 0.31 m ^{3 of} thermal formation water is required for every 1 m ^{3 of} rock.

In the process of development, they control the pressure of high-pressure thermal formation waters.

In addition, this increases the chemical and thermal effects of the contacting surface of the mineralized thermal formation water. For example, an increase in the concentration of calcium chloride in thermal formation water by 1% reduces the equilibrium hydrate formation temperature by 0.5 ° C. In addition, thermal formation water with a high degree of mineralization has a heat capacity that is significantly higher than the heat capacity of fresh water.

The amount of thermal formation water is regulated in accordance with the proposed formula, which allows the most efficient development of the reservoir without the risk of exceeding reservoir pressure above the mountain, excluding the occurrence of uncontrolled hydraulic fracturing.

As a result of the influence of these factors, the degree of gas recovery on the scale of the whole reservoir increases significantly.

Thus, the proposed method in comparison provides continuous operation of the well due to the circulation of produced water.

The probability of self-preservation of hydrates during the implementation of the method is significantly reduced, because there is no decrease in gas temperature at the bottom of the production well, since a gas-liquid mixture is produced, and not pure gas, and the throttle effect is not manifested due to the coolant (thermal waters).

Claims (1)

The method of developing a gas hydrate deposit, which consists in drilling the main well with opening the reservoir and the underlying aquifer, in the drilled well, perforating in the zone of the reservoir and the underlying aquifer, then pumping the tubing to the main well with a submersible pump installation and selection of the gas-liquid mixture at the boundary of the gas-water contact of the reservoir with the simultaneous separation of the gas-liquid mixture in the well and, moreover, gas production is carried out through the annulus, and liquid with dissolved gas through tubing, which is pumped into the underlying aquifer using the aforementioned submersible pump installation, characterized in that at least two bypass wells are drilled additionally the periphery of the reservoir with the opening of the underlying aquifer and carry out their perforation in the zone of the reservoir and the aquifer, in the process of selection of the gas-liquid mixture carry out bypass thermal formation mineralized water from the underlying aquifer to the overlying reservoir for thermal dissociation of the hydrate to ensure circulation of the thermal reservoir water and water of dissociation of the hydrate between the reservoir and the underlying aquifer without raising water to the surface, while in the process of selecting a gas-liquid mixture, pressure is reduced in the bottom-hole zone of the gas hydrate formation to a value that ensures the onset of hydrate dissociation.

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