RU2295632C1 - Method for well drilling and development of multihorizon hydrocarbon field characterized by non-uniform geological conditions of productive bed attitudes - Google Patents

Abstract

FIELD: oil and gas industry, particularly for drilling and development of multihorizon hydrocarbon (oil, gas or gas condensate) field in the case of low-permeable producing reservoir with abnormally high pressure sitting over main object, namely high-permeable producing reservoir, to be developed.

SUBSTANCE: method involves drilling wells to lower reservoir; performing prior bypassing of fluid from high-pressure reservoir into fluid spread zone in low-pressure reservoir under pressure control, wherein the fluid spread zone is bounded by fluid-water contact and above fluid bypassing is carried out under closed well heads; exploiting the reservoirs. Field is developed with well clusters drilled in two stages. At the first stage bypass wells are drilled in each well cluster to provide fluid bypassing from upper high-pressure reservoir into lower low-pressure one. Bypass wells have multi-branch ends terminating inside each reservoir. Impervious barrier, for example cement bridge, is arranged over interval of side well branches drilled in upper low-permeable reservoir. Side branch communicated with lower high-permeable reservoir is drilled over the impervious barrier and then the impervious barrier is penetrated. At the second stage after reservoir pressure reduction within upper high-pressure reservoir opening interval up to value exceeding hydrostatic pressure value by not more than 5-10% producing wells are drilled in each well cluster. Fluid is extracted from lower reservoir.

EFFECT: reduced capital outlays and increased efficiency of total development of both reservoirs.

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Description

The invention relates to the oil and gas industry and can be used in the drilling and development of multilayer hydrocarbon deposits (oil, gas or gas condensate) in the case when a low-permeable production formation with an abnormally high reservoir pressure is located above the main developed object in the form of a highly permeable reservoir, and its development when separate operation is unprofitable.

A known method of developing gas fields, including the development of two or more reservoirs operated by separate well grids with a single land-based arrangement system and combining gas flows from different reservoirs (Zakirov S.N. et al. Design and development of gas fields. M .: Nedra, 1974 ., p. 312). The disadvantage of this method is the increased capital costs when drilling separate grids for each formation.

A known method of developing a multilayer gas or gas condensate field, including drilling production wells and transferring gas from the lower layer to the upper one with pressure control (RF Patent No. 2034131, CL E 21 B 43/00, 04/30/95).

The disadvantages of this method are:

1) the limitation of gas production from the upper development, because it is necessary to maintain the equality of the volumes of gas produced and bypassed, and the lower layer is not actively developed;

2) possible gas losses during bypass into the most permeable interlayers of the upper object in the gas-water contact (GWC) region;

3) an increase in capital expenditures due to an increase in the well stock at the upper main facility and their separate operation;

4) the need to feed a hydrate inhibitor into the wells drilled on the upper low-pressure and low-temperature formation.

A known method of developing multilayer gas fields (RF Patent No. 2135748, class E 21 B 43/16, 43/14, 08/27/99), including drilling production wells on the lower high-pressure formation in an amount that ensures the planned production of gas from the entire field, and preliminary, pressure-controlled, gas bypass before production begins on a single drilled grid of wells from the lower formation to the roof of the upper low-pressure formation with closed wells at the wellhead and before the formation and bottomhole pressures are equal in the interval of opening low upstream reservoir followed by simultaneous joint operation of the upper and lower reservoirs, and when the lower reservoir is flooded, watered wells are transferred to the operation of the upper reservoir.

The disadvantage of this method is the high cost of drilling wells in the case when the overlying productive formation (group of formations) is composed of low-permeability reservoir rocks and has an abnormally high reservoir pressure (ARP), that is, it is more high-pressure compared to the lower located productive reservoir, reservoir pressure in which is equal to or less than hydrostatic. Therefore, in accordance with safety requirements, the opening of the upper formation must be performed with heavier drilling fluids, and to exclude their impact on the reservoir properties of the lower formation and to prevent the absorption of drilling fluid, tight separation of the layers is necessary, for which the upper formation must be covered by casing and cemented, after which opening of the lower layer on more lightweight drilling fluids.

The complication of the design of the well due to the introduction of an additional technical string, the time required to shut off the upper formation and the additional costs of materials (casing, weighting of drilling mud and cement) significantly increase the cost of production wells for the lower highly permeable formation selected as the main development target.

The objective of the invention is to reduce capital costs for drilling wells and increase the efficiency of field development.

To achieve this technical result in the known method of drilling and development of multilayer hydrocarbon deposits with heterogeneous geological conditions of occurrence of productive formations, including:

- drilling production wells at the lower layer selected as the main development object,

- preliminary, pressure-controlled, fluid transfer from the high-pressure formation to the fluid distribution zone in the low-pressure formation, limited by the contact of the fluid with the formation water, with closed wells at the wellhead;

- and subsequent operation of the field,

ACCORDING TO THE INVENTION

- in the case when a low-permeable layer with an abnormally high reservoir pressure is located above the main development object in the form of a lower highly permeable formation, and the field is developed by well clusters, cluster drilling of wells is carried out in two stages:

- at the first stage, bypass wells are drilled at each wellbore, through which fluid is transferred from the upper high-pressure formation to the lower low-pressure formation;

- moreover, the drilling of bypass wells is carried out with multi-lateral horizontal endings in both layers,

- and above the cutoff interval of the sidetracks, an impermeable section is installed in the upper low-permeable formation, for example in the form of a cement bridge, after which a sidetrack is drilled above it onto the lower highly-permeable formation and subsequent drilling of the impermeable section;

- at the second stage, after the reservoir pressure in the interval of opening the upper high-pressure reservoir decreases to a value exceeding the hydrostatic pressure by no more than 5-10%, production wells are drilled on each well,

- and the production of fluid is carried out from the lower reservoir.

Figure 1 shows a diagram of the proposed method, side view, figure 2 is the same, top view.

The inventive method is as follows.

In a multilayer hydrocarbon field, represented by different-permeable reservoirs 1 and 2, separated by an impermeable section, in the case when a low-permeable reservoir 1 with an abnormally high reservoir pressure is located above the main development object in the form of a highly permeable low-pressure reservoir 2, and the development of the upper reservoir 1 during separate operation unprofitable, and the field development scheme involves the production of useful fluid from the lower reservoir 2 by the cluster method, cluster drilling of wells suschestvlyayut in two stages.

At the first stage, bypass wells 3 are drilled at each wellbore to the lower low-pressure formation 2. Selected as the main development object. In this case, the upper low-permeability formation 1 with an abnormally high reservoir pressure is opened by a vertical wellbore with a weighted drilling fluid, the density of which is determined by the necessary excess of hydrostatic pressure above abnormally high reservoir pressure of the upper reservoir.

After lowering the casing and cementing it from the vertical wellbore into the upper formation, lateral shafts 4 with horizontal ends are drilled to accelerate the process of transferring fluid from the upper low-permeability formation 1 to the lower high-permeability formation 2. After this, an impenetrable section is installed above the cutoff interval of the lateral shafts 4 in the casing 5, for example in the form of a cement bridge, followed by drilling of the side trunk 6 with horizontal ends 7 on the lower highly permeable formation 2, and the lateral cutoff interval about the barrel 6 is located above the impenetrable section 5. After drilling the impenetrable section 5, the elevator string of tubing with the equipment regulating and controlling the pressure and quantity of the bypassed fluid is lowered into the vertical shaft, the wellhead is closed and the fluid is transferred from the upper high-pressure formation 1 to the zone fluid distribution in the low-pressure formation 2, limited by the contact of the fluid with formation water.

Fluid bypass is carried out until the reservoir pressure in the opening interval of the upper high-pressure reservoir 1 decreases to a value exceeding the hydrostatic pressure by no more than 5-10%. This value of reservoir pressure allows subsequent drilling of production wells without weighting the drilling fluid when opening the formation 1 and without negative impact of the drilling fluid on the reservoir properties of the formation 2 when opening it.

No gas is produced during the bypass period, and during this time the field is equipped.

Since the upper low-permeability formation 1 is characterized by an abnormally high reservoir pressure, and the pressure in the lower highly-permeable formation 2 is equal to or less than hydrostatic, due to repression, fluid from the upper formation 1 will flow into the lower formation 2. At the same time, the reservoir pressure in the near-stem zone of the horizontal ends 4 of the upper formation 1 will gradually decrease, and reservoir pressure in the near-stem zone of horizontal endings 7 of the lower formation 2 will gradually increase. Thus, drainage zones 8 with a radius constantly increasing in time are formed around the overflow well in formations 1 and 2.

The quantity q of the bypassed fluid from the high-pressure reservoir 1 during the bypass time t is determined from the expression:

where q is the amount of fluid bypassed;

- средний коэффициент гидропроводности для пластов 1 и 2,

- the average coefficient of hydraulic conductivity for reservoirs 1 and 2,

Where

Where

k ₁ and k ₂ - permeability of layers 1 and 2;

h ₁ and h ₂ - effective thickness of layers 1 and 2;

μ is the viscosity of the bypassed fluid;

p _article - pressure in standard conditions;

p ₁ and p ₂ - reservoir pressure in reservoirs 1 and 2;

t is the fluid bypass time;

χ _cf - the average piezoconductivity of formations 1 and 2;

Where

χ _cf - piezoconductivity of formations 1 and 2.

And bottomhole pressures p _1z and p _2z in the interval of opening the upper 1 and lower 2 layers are determined from the expression:

Where

σ is the integration variable;

d is the distance between the faces of the bypass wells.

After the reservoir pressure in the upper high-pressure reservoir 1 is reduced to a value that is not more than 5–10% higher than the hydrostatic pressure, cluster drilling of production wells 9 is carried out, in the construction of which there will be no reservoir pressure due to a decrease in reservoir pressure in the upper reservoir and an increase in reservoir pressure additional casing overlapping the upper formation, and the opening of both layers will be carried out on a lightweight drilling fluid. This will significantly reduce the capital cost of drilling an operating well stock.

After lowering and cementing the production string in the wells 9, perforation is performed in the interval of the lower formation 2, the lift string is lowered and useful fluid is extracted from the lower formation 2.

As the fluid is sampled, reservoir pressure in the lower reservoir 2 will decrease, the pressure differential between the lower 2 and upper 1 reservoirs will increase, which intensifies the flow of fluid from the upper reservoir 1 into the lower reservoir 2.

Thus, the total fluid production from the field will be composed of the volume of fluid production from the lower reservoir 2 and the volume of fluid from the upper reservoir 1, which entered the lower reservoir 2 through overflow wells 3.

Example. During the exploration of one of the multi-layer hydrocarbon deposits in the Tyumen region, two gas deposits were discovered: the upper one is the Senon, confined to the Kuznetsov Formation, and the lower one is the Cenoman, confined to the Pokur Formation, which are characterized by the following parameters:

a) senon

- a depth of 770 m,

- average gas-saturated thickness - 10 m,

- reservoir pressure - 9.5 MPa, i.e. the coefficient of anomalies in reservoir pressure is Ka = 1.23;

- gas reserves - 200 billion m ³ ;

b) cenomanian

- depth of 920 m,

- average gas-saturated thickness - 35 m,

- reservoir pressure - 9.2 MPa,

- gas reserves - 600 billion m ³ .

For the implementation of the proposed method at the stage of exploration, experimental production was carried out, and for this purpose, one of the exploration wells was used as a bypass in the southern part of the field, for which sidetrack 4 was cut and drilled from a vertical well above reservoir 1 with a horizontal end to upper high-pressure formation 1. Above the cutoff interval of the side trunk 4 in the vertical trunk 3, an impenetrable section 5 was installed in the form of a cement bridge, and above it, cut-off and b sidetracking 6 with horizontal ending 7 on the lower highly permeable layer 2.

After drilling the impenetrable section 5 into the vertical shaft, the tubing string was lowered with equipment that regulates and controls the pressure and amount of fluid to be transferred, the wellhead 3 was closed and gas was transferred from the Senon (reservoir 1) to the Senoman (reservoir 2).

Over the course of 2 years, the bottomhole pressure in the senon interval decreased to 7.8 MPa, and in the cenomanian interval it increased to 9.3 MPa. At the same time, the volume of gas supplied from the Cenon to the Cenomanian amounted to 480 million m ³ according to the testimony of the control and regulating equipment, and the radius of the drainage zone according to calculations was: in the Cenon - 1,500 m, and in the Cenomanian - 500 m. Then, operational drilling was carried out on the bush in the amount of four directional wells and gas production from the Cenomanian was carried out.

During the year, gas production from the bush amounted to 100 million m ³ , however, a decrease in reservoir pressure in the Cenomanian was not observed due to the constant supply of gas flowing from the Senon.

Using the proposed method of drilling and development of multilayer hydrocarbon deposits with heterogeneous geological conditions of occurrence of productive formations provides a reduction in capital costs for drilling compared to existing methods and allows you to efficiently generate the resources of both production facilities.

Claims (1)

The method of drilling and development of multilayer hydrocarbon deposits with heterogeneous geological conditions of occurrence of productive formations, including drilling production wells on the lower layer selected as the main development object; preliminary pressure-controlled fluid transfer from the high-pressure formation to the fluid distribution zone in the low-pressure formation, limited by the contact of the fluid with water, with closed wells at the wellhead and subsequent operation of the field, characterized in that when a low-permeable layer with an abnormally high formation pressure is located above the main development object in the form of a lower highly permeable formation, and the field is developed by well clusters, cluster drilling of wells is carried out in two stages: at the first stage, bypass wells are drilled at each wellbore, through which fluid is transferred from the upper high-pressure formation to the lower low-pressure formation; moreover, the drilling of bypass wells is carried out with multi-lateral horizontal endings in both layers, and above the cutoff interval of the sidetracks, an impermeable section is installed in the upper low-permeable formation, for example, in the form of a cement bridge, after which a sidetrack is drilled above it onto the lower highly-permeable formation and subsequent drilling of the impermeable section; at the second stage, after the reservoir pressure in the opening interval of the upper high-pressure reservoir decreases to a value exceeding the hydrostatic pressure by no more than 5-10%, production wells are drilled on each well and the fluid is produced from the lower reservoir.

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