A method for exploiting a shallow heavy oil reservoir near a fault

Abstract

The present application relates to a kind of exploitation method of shallow heavy oil reservoir near fault, belong to the technical field of oil exploitation.The method is:1) in the middle of the oil layer between fault and straight well pattern boundary, the extension direction of horizontal well is consistent with the extension direction of fault;2) from the tip of horizontal well, with at least one straight well development well spacing unit, the horizontal well is segmented;3) each horizontal well section is respectively perforated, and the perforated section corresponding to each horizontal well section is obtained;4) from the tip of horizontal well, in turn, the horizontal well is segmented exploitation, for each horizontal well section to be exploited, first through the perforated section corresponding to horizontal well section to carry out injection viscosity-reducing agent huff and puff exploitation, then steam flooding exploitation is carried out to the straight well located on the boundary of straight well pattern and opposite to horizontal well section, after steam flooding exploitation is ended, the perforated section corresponding to horizontal well section is blocked.The method of the present application not only effectively exploits and uses shallow heavy oil reservoir near fault, but also saves exploitation cost.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, specifically relating to a method for extracting shallow heavy oil reservoirs near faults. Background Technology

[0002] Heavy oil reservoirs are mostly distributed in shallow strata less than 2000 meters deep. Their formation process is often accompanied by biodegradation and oxidation. In addition, due to the influence of tectonic movements and weathering and erosion, natural gas and light hydrocarbon components are lost along faults and erosion surfaces during migration, which further increases the viscosity of heavy oil. In the updip portion of heavy oil reservoirs, heavy oil zones with a certain oil-bearing width are formed along faults. Multiple heavy oil zones accumulate at the fault, forming a considerable amount of heavy oil reserves.

[0003] The aforementioned heavy oil zones concentrated at fault locations exhibit low compressive strength due to the fault acting as a caprock. During conventional steam injection development of heavy oil reservoirs, high-temperature, high-pressure, and high-dryness steam can easily breach the heavy oil zone, carrying a mixture of crude oil and steam condensate along the fault into the shallow groundwater system, and even causing well blowouts, resulting in environmental pollution and property damage. Therefore, for shallow heavy oil reservoirs formed by fault shielding, current technologies typically deploy well networks within the reservoir and control the horizontal distance between the well network boundary and the fault to be greater than one development well spacing, thus avoiding the fault by a certain distance.

[0004] Based on this, the shallow heavy oil reservoirs near faults, that is, shallow heavy oil reservoirs within one development well distance from the fault, have not yet proposed an effective reserve utilization method in the existing exploitation methods, resulting in the uncontrolled reserves of shallow heavy oil reservoirs near faults, which cannot be exploited. Summary of the Invention

[0005] The purpose of this invention is to provide a method for exploiting shallow heavy oil reservoirs near faults, in order to solve the problem that existing exploitation methods are not applicable to the exploitation of shallow heavy oil reservoirs near faults, resulting in uncontrolled reserves and inability to exploit and utilize these reservoirs.

[0006] The technical solution provided by this invention for the exploitation of shallow heavy oil reservoirs near faults to solve the above-mentioned technical problems is as follows: The exploitation method includes the following steps:

[0007] 1) Deploy horizontal wells: Deploy horizontal wells in the oil layer between the fault and the boundary of the vertical well network, wherein the extension direction of the horizontal wells is consistent with the extension direction of the fault;

[0008] 2) Segmenting horizontal wells: Starting from the tip of the horizontal well, segment the horizontal well into sections, using at least one vertical well spacing as the unit;

[0009] 3) respectively perforating the obtained each horizontal well section to obtain a corresponding perforation section of each horizontal well section;

[0010] 4) sequentially performing segmented production on the horizontal well from the horizontal well tip to the horizontal well root, and for each horizontal well section to be produced, performing the following production process: firstly, performing injection of viscosity-reducing agent huff and puff production through the corresponding perforation section of the horizontal well section, then performing steam flooding production on the vertical well located on the boundary of the vertical well network and opposite to the horizontal well section, and after the steam flooding production is completed, plugging the perforation section corresponding to the horizontal well section.

[0011] The beneficial effects of the present application are: 1) the method can be used for production on the basis of the original vertical well network, reducing the time and money cost of new injection well drilling; 2) introducing the horizontal well into the heavy oil reservoir well network as a production well, taking advantage of the large contact length and large drainage area of the horizontal well and the oil layer; 3) using the segmented production method of segmented perforation and step-by-step production, so that the high-temperature and high-pressure steam can fully transfer heat and mass with the shallow heavy oil near the fault, thereby effectively producing and utilizing the shallow heavy oil reservoir near the fault; 4) the segmented production of the present application first performs injection of viscosity-reducing agent huff and puff production, the viscosity of the heavy oil near the perforation section of the horizontal well is reduced, the flow capacity is enhanced, and after a certain degree of heavy oil is produced, the pressure around the perforation section of the horizontal well is reduced, and a certain pressure gradient will be formed in the reservoir between the vertical well and the perforation section of the horizontal well, so that when steam flooding production is performed, the mixture of steam and crude oil is guided to migrate to the perforation section of the horizontal well, and then is produced from the horizontal well, which not only improves the production efficiency, but also effectively guides the flow of steam and crude oil, avoiding the environmental pollution and property loss problems caused by steam breakthrough of the heavy oil zone or the fault.

[0012] Further, the horizontal well is located at the middle position of the fault and the boundary of the vertical well network in the horizontal direction, and is located at the middle and lower part of the oil layer in the vertical direction. By controlling the horizontal distance between the horizontal well and the fault, steam breakthrough of the heavy oil zone can be avoided, and at the same time, the shallow heavy oil near the fault can be utilized, thereby ensuring the stability and controllability of the production process, and improving the production efficiency and utilization degree of the shallow heavy oil reservoir near the fault. By setting the horizontal well at the middle and lower part of the oil layer, gravity can be used to promote the production of the heavy oil reservoir during production, thereby improving the utilization degree of the heavy oil reservoir.

[0013] Further, in step 2), the corresponding horizontal section between each adjacent two vertical wells on the boundary of the vertical well network is divided into a horizontal well section.

[0014] Further, one horizontal well section or two horizontal well sections are produced each time. This can further improve the production efficiency of the shallow heavy oil reservoir near the fault, and ensure the economy of the heavy oil reservoir production.

[0015] Further, in order to ensure the economy of the shallow heavy oil reservoir near the fault, and improve the ratio of oil production and drilling investment, the length of the horizontal well is equal to the length of N vertical well development well spacing, and N is in the range of 4-6.

[0016] Further, the number of rounds of injection and production of the viscosity reducer in step 4) is 3 or 4. Through the injection and production of the viscosity reducer, the heavy oil flow capacity near the horizontal section and the recovery degree can be improved, and the reservoir drive condition between the original vertical well and the horizontal well can be improved, which is beneficial to subsequent steam flooding from the vertical well to the horizontal well.

[0017] Further, the length of the perforation section corresponding to each horizontal well section is M vertical well development well spacing, and M is in the range of 1 / 4-1 / 3.

[0018] Further, the condition for ending the steam flooding in step 4) is that the instantaneous oil-steam ratio of the steam flooding to the perforation section is less than the limit economic oil-steam ratio. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a profile well pattern schematic diagram of an embodiment of the present application;

[0020] Figure 2 is a planar well pattern schematic diagram of a single oil layer of an embodiment of the present application;

[0021] In the figure, 1 is a fault, 2 is an oil layer, 3 is a horizontal well, 4 is a vertical well, 5 is a vertical well perforation section, and 6 is a horizontal well perforation section. DETAILED DESCRIPTION

[0022] The specific embodiments of the present application will be further described below in combination with the drawings.

[0023] The technical concept of the present application is to deploy a horizontal well in the oil layer between the fault and the vertical well pattern; here, the vertical well pattern is the well pattern arranged when the corresponding oil layer heavy oil reservoir is developed in the early stage. From the tip of the deployed horizontal well, the horizontal well is developed in sections; when each section is developed, the section is first perforated to form a perforation section, then injection and production of the viscosity reducer is carried out through the perforation section, and then steam flooding is carried out by injecting steam into the vertical well corresponding to the section, and the perforation section is plugged after the steam flooding is completed. On the basis of the original vertical well pattern, the horizontal well is introduced to take advantage of the large contact length and large drainage area of the horizontal well, and the horizontal well is developed in sections by sectional perforation and sectional production, so that the shallow heavy oil reservoir near the fault can be effectively developed.

[0024] Based on the above technical concept, the method for developing the shallow heavy oil reservoir near the fault of the present application comprises the following steps:

[0025] 1) deploying a horizontal well: deploying a horizontal well in the middle of the oil layer between the fault and the boundary of the straight well pattern, the extending direction of the horizontal well being consistent with the extending direction of the fault;

[0026] 2) segmenting the horizontal well: segmenting the horizontal well from the toe of the horizontal well in units of at least one straight well development well spacing;

[0027] 3) perforating each horizontal well segment obtained respectively to obtain a perforation segment corresponding to each horizontal well segment;

[0028] 4) sequentially segmenting and mining the horizontal well from the toe to the heel of the horizontal well, and for each horizontal well segment to be mined, the following mining process is performed: first, injecting a viscosity-reducing agent and conducting huff and puff mining through the perforation segment corresponding to the horizontal well segment, then conducting steam flooding mining on the straight well located on the boundary of the straight well pattern and opposite to the horizontal well segment, and sealing the perforation segment corresponding to the horizontal well segment after the steam flooding mining is completed.

[0029] As a preferred embodiment, the deployment position of the horizontal well is: in the horizontal direction, the horizontal well is deployed in the oil layer between the fault and the boundary of the straight well pattern, and is located at the middle position of the fault and the boundary of the straight well pattern; in the vertical direction, the horizontal well is located in the middle and lower part of the oil layer. Specifically, when the horizontal distance between the boundary of the straight well pattern and the fault is 1.0 length of the straight well pattern development well spacing, the horizontal distance between the horizontal well and the fault is 0.5 length of the straight well pattern development well spacing. By controlling the horizontal distance between the horizontal well and the fault, steam breakthrough in the heavy oil zone can be avoided, while the shallow heavy oil near the fault can be produced, thereby ensuring stable and controllable mining process and improving the mining efficiency and producing degree of the heavy oil reservoir near the fault. By setting the horizontal well in the middle and lower part of the oil layer, gravity can be used to promote the production of the heavy oil reservoir during mining, thereby improving the producing degree of the heavy oil reservoir.

[0030] As a preferred embodiment, when segmenting the horizontal well, the horizontal well is segmented from the toe of the horizontal well in units of one straight well development well spacing or two straight well development well spacings. Since the horizontal well is segmented in units of straight well development well spacing, each horizontal well segment corresponds to at least one straight well on the boundary of the straight well pattern, and when the toe of the horizontal well is directly aligned with the boundary of the straight well pattern, each horizontal well segment corresponds to at least two straight wells, as shown in Figure 2 .

[0031] When the horizontal well is segmented in units of one straight well development well spacing, the horizontal segment corresponding to each adjacent two straight wells on the boundary of the straight well pattern is divided into one horizontal well segment.

[0032] When the horizontal segment between any two adjacent vertical wells on the boundary of a vertical well network is designated as a horizontal segment, one or two horizontal segments are extracted at a time. That is, each time one horizontal segment corresponding to two adjacent vertical wells is selected for extraction, or two horizontal segments corresponding to three adjacent vertical wells are combined for extraction. This can further improve the extraction efficiency of shallow heavy oil reservoirs near faults and ensure the economic viability of heavy oil reservoir extraction.

[0033] Each time a horizontal well section corresponding to two adjacent vertical wells is selected for production, viscosity-reducing agent is first injected through the perforated section of that horizontal well section for production. Then, steam is injected into the two adjacent vertical wells corresponding to that horizontal well section for steam drive production. After the steam drive production is completed, the perforated section of that horizontal well section is sealed. Then, the production process is repeated for the next horizontal well section until the root of the horizontal well is reached.

[0034] When selecting two horizontal well sections corresponding to three adjacent vertical wells for combined production, the process begins with injection of viscosity-reducing agents through the perforated sections of each of these two horizontal well sections. Then, steam is injected into the three adjacent vertical wells corresponding to these two horizontal well sections for steam-driven production. After steam-driven production is completed, the perforated sections of the two horizontal well sections are sealed. This process is then repeated for the next two horizontal well sections until the root of the horizontal well is reached.

[0035] When dividing horizontal wells into segments based on the distance between two vertical wells, the horizontal segment between every three adjacent vertical wells on the boundary of the vertical well network is designated as a horizontal well segment. Each horizontal well segment can have one perforation segment or two perforation segments, depending on the length of the perforation segment and the length of the horizontal well segment.

[0036] In a preferred embodiment, the length of the horizontal well is equal to the length of the development well spacing of 4 to 6 vertical wells. This arrangement ensures the economic viability of utilizing shallow heavy oil reservoirs near faults and increases the ratio of oil production to drilling input.

[0037] In a preferred embodiment, the number of cycles of viscosity-reducing injection and huff-and-puff production is 3 to 4 in each stage of production. By injecting and huff-and-puffing viscosity-reducing agents, the flow capacity and recovery rate of heavy oil near the horizontal section can be improved, and the reservoir driving conditions between the original vertical and horizontal wells can also be improved, which is conducive to subsequent steam drive production from vertical wells to horizontal wells.

[0038] In a preferred embodiment, the length of each perforation section is 1 / 4 to 1 / 3 of the length of the well spacing in the vertical well network.

[0039] As a preferred embodiment, in each segmented mining operation, steam-driven mining ends when the instantaneous oil-steam ratio in the perforation section is less than the limit economic oil-steam ratio.

[0040] The following example of a shallow heavy oil reservoir near a fault will be used to further illustrate the specific implementation process of the present invention.

[0041] The shallow heavy oil reservoir near this fault is buried at a depth of 190m. Its structure is a monocline with a dip angle of 12°, an average oil layer thickness of 4.1 meters, a porosity of 0.3, a permeability of 1300 mD, and an initial oil saturation of 0.7. At the reservoir temperature (27.60℃), the viscosity of the degassed crude oil is 31600 mPa·s, and the initial formation pressure is 2.1–2.6 MPa. This is an extra-heavy oil reservoir shielded by a fault.

[0042] Because the oil reservoir is shallow, deploying development wells near the fault for steam injection could easily cause steam to flow along the fault, contaminating shallow groundwater or causing surface eruptions. Therefore, in the main area away from the fault, a network of vertical wells was deployed with a well spacing of 100m. After 25 years of steam injection and production, with an average of 11 injection cycles, the formation pressure dropped to 0.5MPa, the daily oil production per well was 0.44t / d, the oil-steam ratio was 0.16, and the recovery rate was 21.3%, indicating that the reservoir has entered a low-production and low-efficiency stage. Meanwhile, no development wells have been deployed in the oil layer near the fault, and the geological reserves have remained unexploited.

[0043] Reference for well pattern distribution of exploitation methods for shallow heavy oil reservoirs near this fault Figure 1 The schematic diagram of the well pattern is shown below. This diagram illustrates the exploitation of a shallow heavy oil reservoir near fault 1, including two oil layers 2. The exploitation method for a single oil layer near a fault is illustrated below. The well pattern distribution for a single oil layer is referenced. Figure 2 A schematic diagram of the planar well network shows the following steps for the exploitation of shallow heavy oil reservoirs near the fault:

[0044] (1) A new horizontal well 3 is drilled in the oil layer between the fault oil-bearing interface and the existing vertical well network. After the horizontal well 3 is completed, casing is run and cemented. The existing vertical well network is the well network arranged when the corresponding oil layer heavy oil reservoir was exploited in the early stage. The boundary of the existing vertical well network consists of 7 vertical wells 4, which are numbered A to G in sequence. The horizontal distance between each adjacent vertical well 4 and the horizontal distance between the boundary of the vertical well network and the inner boundary of the fault are both 70 meters (the length of 1.0 vertical well network development well spacing). The newly drilled horizontal well is located in the middle and lower part of the oil layer in the vertical direction. The length of the horizontal section is 400 meters (the length of nearly 6 vertical well network development well spacing). The horizontal distance between the horizontal well and the inner boundary of the fault is 35 meters.

[0045] (2) Starting from the tip of the deployed horizontal well, select two sections corresponding to three adjacent vertical wells and combine them together for production. Specifically, select the first and second sections corresponding to vertical wells A and B, and vertical wells B and C, and perforate the first and second sections respectively. A horizontal well perforation section 6 is obtained between every two vertical wells. The length of the horizontal well perforation section 6 is 20-30 meters, which are the first perforation section and the second perforation section respectively. Viscosity reducing agent injection and production are carried out through the first and second perforation sections, preferably in 4 cycles. Then, steam is injected through vertical wells A, B, and C through the vertical well perforation section 5, and production is carried out through the first and second perforation sections using horizontal well 3, for steam drive production. When the instantaneous oil-steam ratio of the perforation section is less than 0.2, the steam drive production ends, and the first and second perforation sections are sealed.

[0046] (3) Select the third and fourth sections corresponding to vertical wells C and D, and vertical wells D and E, and perforate these sections. A horizontal perforation section 6 is obtained between every two vertical wells, with a length of 20-30 meters, designated as the third and fourth perforation sections. Viscosity-reducing agents are injected and pumped through the third and fourth perforation sections for four cycles. Then, steam is injected through vertical wells C, D, and E via the vertical perforation section 5, and production is carried out through the third and fourth perforation sections via horizontal well 3, for steam-driven production. Steam-driven production ends when the instantaneous oil-steam ratio in the perforation section is less than 0.2, and the third and fourth perforation sections are sealed.

[0047] (4) Select the fifth and sixth sections corresponding to vertical wells E and F, and vertical wells F and G. A horizontal well perforation section 6 is obtained between every two vertical wells, with a length of 20-30 meters, representing the fifth and sixth perforation sections respectively. Viscosity-reducing agent injection and churn production is carried out through the fifth and sixth perforation sections, with four churn cycles. Then, steam is injected through vertical wells E, F, and G via the vertical well perforation section 5, and production is carried out through horizontal well 3 via the fifth and sixth perforation sections, for steam-driven production. When the instantaneous oil-steam ratio in the perforation section is less than 0.2, steam-driven production ends, and the fifth and sixth perforation sections are sealed.

[0048] After six years of production using the above extraction methods, the uncontrolled reserves of heavy oil near the fault were utilized, with an extraction rate of 19.4%, close to the extraction rate of the main production area.

Claims

1. A method for exploiting shallow heavy oil reservoirs near a fault, wherein the shallow heavy oil reservoir near the fault is a shallow heavy oil reservoir within one development well distance of the fault, characterized in that, The mining method includes the following steps: 1) Deploying horizontal wells: Horizontal wells are deployed in the oil layer between the fault and the boundary of the vertical well network. The extension direction of the horizontal well is consistent with the extension direction of the fault. The length of the horizontal well is equal to the length of 4 to 6 vertical well development wells. 2) Segmenting horizontal wells: Starting from the tip of the horizontal well, segment the horizontal wells using at least one vertical well development distance as a unit; when segmenting the horizontal wells using one vertical well development distance as a unit, the horizontal segment corresponding to each two adjacent vertical wells on the boundary of the vertical well network is divided into a horizontal well segment; 3) Perforate each of the obtained horizontal well sections to obtain the perforated section corresponding to each horizontal well section. The length of the perforated section corresponding to each horizontal well section is 1 / 4 to 1 / 3 of the vertical well development well spacing. 4) From the tip of the horizontal well to the root of the horizontal well, the horizontal well is sequentially segmented for mining. Each time, one or two horizontal well segments are mined. For each horizontal well segment to be mined, the following mining process is carried out: First, viscosity-reducing agent is injected and pumped through the perforated section corresponding to the horizontal well segment. Then, steam drive mining is carried out on the vertical well located on the boundary of the vertical well network and opposite to the horizontal well segment. After the steam drive mining is completed, the perforated section corresponding to the horizontal well segment is sealed.

2. The method for exploiting shallow heavy oil reservoirs near faults according to claim 1, characterized in that, The horizontal well is located in the middle of the boundary between the fault and the vertical well network in the horizontal direction, and in the middle and lower part of the oil layer in the vertical direction.

3. The method for exploiting shallow heavy oil reservoirs near faults according to claim 1, characterized in that, In step 4), the number of cycles of injection of viscosity reducer during the huff and puff process is 3 or 4.

4. The method for exploiting shallow heavy oil reservoirs near faults according to claim 1, characterized in that, In step 4), the condition for the end of steam-driven mining is that the instantaneous oil-steam ratio at the perforation section is less than the limiting economic oil-steam ratio.

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