RU2827198C1 - Method for development of oil deposit by horizontal wells - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention relates to a method of developing an oil deposit by horizontal wells. Method includes determining directions of maximum permeability of oil-saturated rocks. Also includes drilling of production wells with horizontal shafts in direction maximum permeability with multistage hydraulic fracturing. It also involves drilling of additional horizontal wells perpendicular to direction of maximum permeability of oil-saturated rocks and between fractures of hydraulic fracturing with deep perforation along the entire horizontal borehole. Initial formation pressure, direction of maximum permeability of oil-saturated rocks and oil-water contact (OWC) are preliminary determined, horizontal shafts of production wells are drilled with azimuth shift of not more than 20° in direction of maximum permeability of oil-saturated rocks or in their direction, production of products from production wells is performed. If the product is flooded by more than 98%, production wells are transferred to injection wells; multi-stage hydraulic fracturing is performed with creation of fractures perpendicular to the borehole. Additional production wells are drilled with horizontal shafts with a length of at least 350 m and/or a length corresponding to the distance between two additional horizontal wells, horizontal shafts of production wells are located perpendicular to direction of maximum permeability of oil-saturated rocks, parallel to OWC at a distance of at least 3 m from the OWC and between hydraulic fracturing cracks with a distance greater than 150 m from the trajectory of the hydraulic fracturing cracks, perforation is performed along the whole horizontal borehole along a spiral with depth of 1.8-2.0 m each hole and distance from each other from 8 to 10 m in each well. At 40% decrease of formation pressure from initial formation pressure in the transferred injection wells, water injection into the formation with volume of 1.2 of the volume of the produced product is started, maintaining the formation pressure at the initial level.

EFFECT: provision of uniform oil displacement from oil-saturated formation, high rate of oil extraction and increase of well productivity.

1 cl, 1 dwg, 1 tbl

Description

The invention relates to the oil producing industry, in particular to methods for developing hard-to-recover oil reserves of dense, non-uniform permeability deposits at a late stage, namely carbonate deposits of the Bashkirian stage.

A known method of reservoir development (article "New approaches to the use of horizontal wells in waterflooding", Socar Proceedings, 2023) includes placing a horizontal injection wellbore in the direction of minimum horizontal formation stresses, performing multi-stage hydraulic fracturing with the creation of fractures transverse to the wellbore. Production horizontal wells are drilled along the direction of maximum horizontal stresses, perform multi-stage hydraulic fracturing with the creation of fractures longitudinal to the wellbore and are placed in the middle between the initiation points of hydraulic fracturing fractures of the injection well at a distance exceeding 150 m from the trajectory of the injection well fractures. This minimizes the risk of the auto-fracturing fracture trajectory intersecting during injection with the trajectory of the production well.

The disadvantage of this method is that in the direction of the minimum horizontal stresses of the formation, a horizontal injection well is immediately placed without working off oil.

The shift from azimuth in the direction of maximum permeability of oil-saturated rocks is not taken into account.

A small volume of drained rock around horizontal production wells. All this reduces the oil recovery of the field and the economic effect of using this technology.

A method is known for developing a heterogeneous oil reservoir with water-oil zones (RU patent No. 2282022, IPC E21B 43/20, published on 20.08.2006), including measurements of oil, water and water injection production to clarify the current development conditions and modeling of the reservoir development process, determining the minimum distance from the penetrated interval to the water-oil contact, at which premature flooding of the well production does not occur, drilling branched horizontal and/or subhorizontal wells, wherein the main horizontal and/or subhorizontal wellbore is located above the water-oil contact at a minimum distance ensuring a water-free period of well operation, and horizontal and/or subhorizontal and/or vertical branches are drilled along an ascending profile with the same azimuth as the main horizontal and/or subhorizontal wellbore and/or moving away from it towards the roof of the productive layer or interlayer.

According to this method, the arrangement of the main horizontal and/or subhorizontal well bores and the placement of branches ensures a reduction in the amount of produced water and an increase in the service life of the wells. The method allows for an increase in the displacement coefficient.

The disadvantage of this method is: part of the formation below the main horizontal wellbore remains undrained and when one interval of the main horizontal and/or subhorizontal wellbore is flooded, it is problematic, almost impossible, to isolate the water inflow. All this reduces the oil recovery of the field and the economic effect of using this technology. And also high costs for drilling horizontal branches.

Also known is a method for developing low-permeability oil deposits using horizontal wells with transversely directed hydraulic fracturing cracks (RU patent No. 2515628, IPC E21B 43/18, 43/30, published on 20.05.2014 in Bulletin No. 14), which includes drilling horizontal production wells, with a row arrangement of wells and orientation of horizontal wellbores in the direction of minimum horizontal formation stresses, and performing multi-stage hydraulic fracturing on the said horizontal production wells. Parallel to the rows of horizontal production wells, alternating every other row, rows of directional injection wells are drilled with hydraulic fracturing performed on all wells, while on the injection wells located opposite the middle of the length of the horizontal wellbore of the production wells, hydraulic fracturing and commissioning are carried out at the stage when all neighboring wells have already been commissioned: the nearest horizontal production wells in neighboring rows are commissioned for production, the nearest injection wells in the row are commissioned for injection, and the injection of fluid on the directional injection wells is carried out at a bottomhole pressure exceeding the formation fracture pressure.

The disadvantages of this method are that the main development of reserves occurs in the zone of maximum permeability, without covering the zone of minimum permeability. It is possible to flood the formation ahead of schedule due to the arrangement of wells with alternation through one row.

Also known is a method for developing a low-permeability reservoir with sequential initiation of auto-HF cracks (RU patent No. 2745058, IPC E21B 43/267, published on 18.03.2021 in bulletin No. 8), including: carrying out multi-stage hydraulic fracturing (MSHF) using a hydraulic fracturing fluid containing a proppant in at least two wells, the horizontal wellbores of which are located with an azimuth offset of 20 to 160 degrees relative to the direction of the maximum horizontal stress in the formation, determining the closure pressure during research in at least one well, subsequently used as an injection well, and carrying out production; using at least one of the above-mentioned wells as an injection well by pumping a working fluid into it with an injection pressure exceeding the hydraulic fracturing pressure (HF); ensuring a breakthrough of the working fluid from the injection well through at least one self-HF crack into at least one well in production mode (a production well); performing production from the production well and stopping the injection well when the fluid water cut in the production well reaches from 60% to 95%; continuing production from the production well and recording a decrease in the bottomhole pressure in the injection well; when the closure pressure value in the injection well is reached or below this value, repeating the previous four stages until at least one more self-HF crack is activated in this injection well.

The disadvantage of this method is that premature flooding is possible due to the fact that the location and distance of production wells with the direction of hydraulic fracturing cracks are not taken into account.

The closest in technical essence is the method for developing low-permeability oil deposits (patent RU No. 2547848, IPC E21B 43/263, 43/30, published on 10.04.2015 in Bulletin No. 10), which includes drilling production and injection wells using a row development system, with hydraulic fracturing (HF) at all wells, placing rows of injection and production wells in parallel and alternating every other one in the direction of maximum horizontal stresses of the formation. Production and injection wells are drilled with horizontal wellbores in the direction of maximum horizontal stresses with multi-stage HF.

The disadvantages of this method are:

- low efficiency due to the use of a template row development system, which may not be effective in the carbonate deposit of the Bashkirian stage, where it is important to take into account the rheological parameters of the productive formation. Part of the formation below the main horizontal wellbore remains undrained, premature formation flooding is possible due to the displacement front from injection wells located on both sides of the production well;

- low productivity of the method, associated with the limitation of the length of the hydraulic fracture depending on the features of the mechanical properties profile and the number of stages with a fixed length of the horizontal wellbore due to the longitudinal location of the hydraulic fractures to the wellbore.

The technical result is to ensure uniform displacement of oil from an oil-saturated formation, a high rate of oil recovery and an increase in well productivity due to the use of a developed well grid, which allows for maximum coverage of the reservoir drainage by area by using horizontal technology and a section by increasing the volume of drained rock around a horizontal wellbore using deep perforation, connecting the maximum possible thickness in a heterogeneous oil-bearing reservoir to drainage.

The technical result is achieved by a method of developing an oil deposit using horizontal wells, including determining the directions of maximum permeability of oil-saturated rocks, drilling production wells with horizontal wellbores in the direction of maximum permeability with multi-stage hydraulic fracturing of the formation, drilling additional horizontal wells perpendicular to the direction of maximum permeability of oil-saturated rocks and between hydraulic fracturing cracks with deep perforation along the entire horizontal wellbore.

What is new is that the initial reservoir pressure, the direction of maximum permeability of oil-saturated rocks and the water-oil contact (WOC) are preliminarily determined, horizontal wellbores of production wells are drilled with an azimuth offset of no more than 20° in the direction of maximum permeability of oil-saturated rocks or in their direction, production is produced from production wells, when the water cut of the product is higher than 98%, production wells are converted into injection wells, multi-stage hydraulic fracturing is performed with the creation of fractures perpendicular to the wellbore, while additional production wells are drilled with horizontal wellbores no less than 350 m long and/or a length corresponding to the distance between two additional horizontal wells, horizontal wellbores of production wells are located perpendicular to the direction of maximum permeability of oil-saturated rocks, parallel to the WOC at a distance of no less than 3 m from the WOC and between the hydraulic fracturing fractures at a distance exceeding 150 m from the trajectory of the hydraulic fracturing fractures, perforation along the entire horizontal wellbore in a spiral with a depth of 1.8-2.0 m for each hole and a distance from each other from 8 to 10 m in each well. When the reservoir pressure decreases by 40% from the initial reservoir pressure in the converted injection wells, water is injected into the reservoir with a volume of 1.2 of the volume of the extracted product, maintaining the reservoir pressure at the initial level.

Fig. 1 shows a diagram of a well grid used to develop an oil deposit, where 1 is a horizontal production well that is later converted into an injection well, 2 is a hydraulic fracture, 3 is an additional horizontal production well.

The essence of the method is as follows.

Initial reservoir pressure is determined in advance. The direction of maximum permeability of oil-saturated rocks, OWC, is determined.

The horizontal shafts of production wells 1 are drilled with an azimuth offset of no more than 20° in the direction of maximum permeability of oil-saturated rocks or in their direction. The location of production wells 1 with a minimum deviation or in the direction of maximum permeability creates a zone between wells in the carbonate deposit of the Bashkirian stage, which ensures the initial maximum possible production of the productive formation due to the consideration of the rheological parameters of the productive formation, in which the formation fluid located in the matrix of the carbonate formation of the Bashkirian stage is not blocked by water filtering through cracks. And also allows in the process of further multi-stage hydraulic fracturing to obtain longitudinal cracks of hydraulic fracturing.

They extract products from production wells 1 with water cut measurements.

When the water content of the production exceeds 98%, horizontal production wells 1 are converted into injection wells.

In the converted injection wells, multi-stage hydraulic fracturing is performed with the creation of fractures perpendicular to the wellbore 2.

In this case, additional production wells 3 are drilled with horizontal wellbores no less than 350 m long and/or the length corresponding to the distance between two additional horizontal wells. The horizontal wellbores of production wells 3 are located perpendicular to the direction of maximum permeability of oil-saturated rocks, parallel to the OWC at a distance of no less than 3 m from the OWC in the water-oil zone and between the hydraulic fractures at a distance exceeding 150 m from the trajectory of the hydraulic fractures. Such an arrangement of additional production wells 3 minimizes the risk of intersection of the trajectory of the hydraulic fractures during injection of the displacing agent with the trajectory of the production well, and also increases the maximum coverage of the reservoir by drainage area and the volume of the drained rock of the productive formation around the horizontal production wells, as a consequence increasing the productivity of the wells.

In additional horizontal production wells 3, perforation is performed along the entire horizontal wellbore in a spiral with a depth of 1.8-2.0 m for each hole and a distance from each other from 8 to 10 m in each well. Such perforation allows to involve hydrocarbon reserves that are produced for some reason much more slowly or are practically not produced at all with the existing measures of influence on the formation, i.e. to develop stagnant and poorly drained zones of the oil deposit in the formation. The volume of drained rock is increased, connecting the maximum possible thickness in a heterogeneous oil deposit to drainage. In this way, an active development system is created using waterflooding at the objects of the carbonate deposit of the Bashkirian stage with extremely low permeability, ensuring a long water-free period of operation of production wells.

Next, oil is extracted from additional production wells 3.

When the reservoir pressure decreases by 40% from the initial reservoir pressure, in order to avoid the closure of natural cracks, water is pumped into horizontal injection wells. As a result of multi-stage hydraulic fracturing at such reservoir pressure, the development of a hydraulic fracture occurs mainly in length.

Water is pumped into the formation in a volume of 1.2 of the volume of the extracted product, maintaining the formation pressure at the initial level. In this way, the energy of the productive formation is replenished. A certain volume of injection ensures the entrainment of the injected displacing agent with oil from the well, pulling the oil to the zone located between the plane of the water-oil contact and the perforation interval in additional production wells, thus artificially creating an oil-water saturated zone. Provides a high rate of oil extraction.

Example of specific implementation

Initial reservoir pressure was preliminarily determined to be 8.4 MPa. Hydrodynamic studies (hydraulic listening) were conducted and the direction of maximum permeability of oil-saturated rocks was determined. The oil-oil contact was determined at the 723 m mark.

The horizontal wells of production wells 1 were drilled along the direction of maximum permeability. Production was produced from production wells with water cut measurement. The oil flow rate of two horizontal production wells 1 in the area was 42 tons/day.

When the production was 98% flooded, the horizontal production wells 1 were converted into injection wells. Multi-stage hydraulic fracturing was performed with the creation of fractures perpendicular to the wellbore.

At the same time, additional production wells 3 were drilled with horizontal wellbores located at a distance of 350 m from each other and perpendicular to the direction of maximum permeability of oil-saturated rocks, parallel to the oil-oil contact at the mark of -719 m and between hydraulic fractures at a distance of 160 m from the trajectory of hydraulic fractures.

In additional production wells 3, perforation was performed along the entire horizontal wellbore in a spiral with holes 1.8 m deep each and 9 m apart. Oil production is underway with a total flow rate of two horizontal production wells in the area of 27 tons/day.

When the reservoir pressure dropped to 5 MPa, water injection began in the converted injection wells at a volume of 51 ^m3 /day, maintaining the reservoir pressure at the initial level of 8.4 MPa.

Oil was then extracted from additional production wells. The flow rate of two horizontal production wells was 35 tons/day (Example 1, Table).

The remaining examples of implementing the method are carried out similarly, their conditions of implementation and results are given in the table (examples 2-4).

Thus, the proposed method ensures uniform displacement of oil from an oil-saturated formation, a high rate of oil recovery and an increase in well productivity due to the use of a developed well grid, which allows for maximum coverage of the reservoir drainage by area by using horizontal technology and section by increasing the volume of drained rock around the horizontal wellbore using deep perforation, connecting the maximum possible thickness in a heterogeneous oil-bearing reservoir to drainage.

Table - Conditions and results of the implementation of the method of developing an oil deposit using horizontal wells

Example No. Initial reservoir pressure, MPa Location of horizontal production wells Flow rate of production wells, t/day Flow rate of additional production wells, t/day Water cut in production wells, % Length of horizontal shaft of additional production well, m Perforation hole depth, m Distance between perforation holes, m Volume of displacing agent, ^m3 /day Displacing agent injection pressure, MPa 1 8.4 along the direction of maximum permeability 42 35 98 350 1.8 9 51 9.2 2 8.4 with an azimuth offset of 10° in the direction of maximum permeability 39.7 33 98 350 1.8 10 51 9.2 3 8.4 with an azimuth offset of 20° in the direction of maximum permeability 37.9 37 98 350 2.0 9 51 9.2 8.4 along the direction of maximum permeability 42 40 98 400 2.0 9 51 9.2 4 8.4 with an azimuth offset of 30° in the direction of maximum permeability 28.1 36 98 400 2.0 10 51 9.2

Claims (1)

A method for developing an oil reservoir using horizontal wells, including determining the directions of maximum permeability of oil-saturated rocks, drilling production wells with horizontal wellbores in the direction of maximum permeability with multi-stage hydraulic fracturing of the formation on them - HF, drilling additional horizontal wells perpendicular to the direction of maximum permeability of oil-saturated rocks and between HF cracks, with deep perforation along the entire horizontal wellbore, characterized in that the initial reservoir pressure, the direction of maximum permeability of oil-saturated rocks and the water-oil contact - OWC are preliminarily determined, horizontal wellbores of production wells are drilled with an azimuth offset of no more than 20° in the direction of maximum permeability of oil-saturated rocks or in their direction, production of products is carried out from production wells, when the water cut of the product is higher than 98%, production wells are converted into injection wells, multi-stage HF is performed with the creation of cracks perpendicular to the wellbore, while drilling additional production wells with horizontal wellbores no less than 350 m long and/or a length corresponding to the distance between two additional horizontal wells, horizontal wellbores of production wells are located perpendicular to the direction of maximum permeability of oil-saturated rocks, parallel to the OWC at a distance of no less than 3 m from the OWC and between hydraulic fractures at a distance exceeding 150 m from the trajectory of the hydraulic fractures, perforation is performed along the entire horizontal wellbore in a spiral with a depth of 1.8-2.0 m for each hole and a distance from each other from 8 to 10 m in each well, when the reservoir pressure decreases by 40% from the initial reservoir pressure in the converted injection wells, water injection into the reservoir with a volume of 1.2 of the volume of produced products begins, maintaining the reservoir pressure at the initial level.