A carbonate karst cave-fracture type reservoir well site deployment method

Abstract

The application discloses a carbonate karst cave-crack type reservoir well site arrangement method, relates to a natural gas exploitation technical field, and solves the problems of great well arrangement difficulty, low success rate and the limitation of well arrangement technology of an existing well arrangement method. The method is characterized in that: a structure line, a fault line, a stratum line, a physical property line and an oil-water boundary line are used to delineate the boundary of an oil and gas reservoir, fine interpretation of the oil and gas reservoir, structure and fracture is realized, the prediction and description of special lithology are used as the identification of a while-drilling marker layer, geological sublayer division, comparison and reservoir prediction define the position and interbedded layer of the reservoir, reservoir seismic reflection type division is carried out, the horizontal well trajectory is optimized, the best trajectory direction is perpendicular to or large-angle oblique to the maximum ground stress, the well arrangement mode of a pilot hole and a horizontal well horizontal segment with a length of 1500-2000 meters is used to arrange the well, and the well trajectory passes through intermittent seismic reflection and passes through a seismic tower-shaped reflection. The well arrangement method is reasonable, and the reservoir drilling rate is improved.

Description

Technical Field

[0001] This invention relates to the field of natural gas extraction technology, specifically to a method for well site deployment in a carbonate karst cave-fracture reservoir that integrates seismic, geological, and gas reservoir engineering considerations. Background Technology

[0002] Carbonate reservoirs hold a significant position in global oil and gas distribution, accounting for approximately 50% of the world's total reserves and over 60% of global production. The carbonate reservoirs in the study area have transitioned from the exploration to the development stage. Currently, well placement is primarily focused on structural high points. In the past two years, the success rate of drilling and completing reservoirs has been relatively high, generally around 80%. However, the success rate of drilling and uncovering fractured-vuggy reservoirs has been lower, with no major breakthroughs achieved, drastically increasing the difficulty of well placement. While well placement at structural high points has yielded good initial results, good quality cavernous reservoirs are becoming increasingly scarce. If the remaining reservoirs have underdeveloped fractures and small caverns, high efficiency with a single well is difficult. Besides the specific geological limitations, fractured-vuggy carbonate gas reservoirs also face technical challenges and limitations from different professional fields. For example, using seismic methods for well placement results in a low success rate due to topographical influences and resolution limitations; fractured-vuggy and pore-type reservoirs have poor physical properties, are prone to contamination, and require reservoir stimulation, demanding higher levels of technological expertise.

[0003] This invention aims to address the deficiencies and shortcomings of the existing technologies by providing a well placement method for carbonate cave-fracture reservoirs. This invention addresses the complex geological characteristics of carbonate reservoirs, such as heterogeneity and lateral variations in gas layers, by employing a reasonable well placement method that improves reservoir encounter rate. It achieves a leading domestic overall success rate in exploration and development drilling (92%), enabling high and stable production from single wells and saving significant funds. Summary of the Invention

[0004] To address the problems of high difficulty, low success rate, and limitations of existing well placement methods, this invention provides a well placement method for carbonate karst cave-fracture reservoirs.

[0005] A well location deployment method for carbonate karst cave-fracture reservoirs, comprising the following steps:

[0006] Step 1: Based on the geological characteristics of carbonate reservoirs, use structural lines, fault lines, stratigraphic lines, physical property lines, and oil-water boundary lines to delineate the boundaries of oil and gas reservoirs, thereby achieving a detailed interpretation of the reservoir structure and fractures.

[0007] Step 2: Use the prediction and description of special lithology as the basis for identifying marker layers during drilling, and carry out geological sub-layer division, comparison and reservoir prediction to define the location and interlayers of interlayer karst reservoirs;

[0008] Step 3: Based on the interlayer karst reservoirs described in Step 2, classify them according to reservoir seismic reflection type; these are divided into tower-shaped seismic reflection, discontinuous seismic reflection, and chaotic seismic reflection types.

[0009] Step 4: Based on the distribution of the interlayer karst reservoir, optimize the horizontal well trajectory and determine the optimal horizontal well trajectory direction to be perpendicular to or at a large angle to the maximum geostress.

[0010] Step 5: Well placement is carried out using a method where the horizontal section of the pilot well and horizontal well is 1500-2000 meters long, and the well trajectory passes through discontinuous seismic reflections and seismic tower-like reflections.

[0011] Furthermore, the specific process of step one is as follows:

[0012] Step 11: Process the seismic data volume: Apply seismic-well logging combined impedance inversion technology, pre-stack fracture prediction technology, and carbonate paleogeographic analysis technology to perform fracture interpretation and stratigraphic tracing.

[0013] Steps 1 and 2: Based on core, well logging, and seismic data, analyze reservoir lithology, reservoir space type, degree of filling of fractured-vuggy reservoirs, and the variation of the degree of filling of fractured-vuggy reservoirs in the vertical and horizontal directions.

[0014] Step 13: Combining static and dynamic data, based on single wells and through multi-well profile comparison, study the vertical and horizontal connectivity of the reservoir, inter-well connectivity, and oil, gas and water boundaries to achieve a detailed interpretation of oil and gas reservoirs, structures, and fractures.

[0015] Furthermore, in step two, special lithology refers to rock types that differ from the lithology of adjacent strata.

[0016] Furthermore, the specific process of step two is as follows:

[0017] Step 21: Divide the geological sub-layers according to lithology and cycle.

[0018] Step 22: Divide the geological sub-layers identified in Step 21 according to their composition, and use the high-gamma mudstone section as the marker layer during drilling.

[0019] Furthermore, in step three, the tower-shaped seismic reflection type is the cave type: the output is related to the size of the cave; it is divided into large caves, medium caves and small caves.

[0020] Furthermore, the discontinuous seismic reflection type is formed by the connection of small karst caves, and the production level is related to the degree of crack development.

[0021] Furthermore, the more developed the fractures, the higher the yield; conversely, the less developed the fractures, the lower the yield. The oil yield in areas with developed fractures is above 200,000 cubic meters per day, the oil yield in areas with underdeveloped fractures is between 100,000 and 200,000 cubic meters per day, and the oil yield in areas with undeveloped fractures is <100,000 cubic meters per day.

[0022] Furthermore, the chaotic seismic reflection type is characterized by low production, with oil production in fracture-developed areas below 50,000 cubic meters per day.

[0023] Furthermore, in step four, the interlayer karst reservoir is distributed in a quasi-layered manner, and the horizontal well trajectory is optimized by using geostress field prediction and engineering geomechanics.

[0024] Furthermore, in step four, the optimal horizontal well trajectory direction is determined to be perpendicular to or oblique to the maximum ground stress at a large angle, with the large angle ranging from 50 to 60 degrees.

[0025] The beneficial effects of this invention are:

[0026] The reservoir well placement method described in this invention is designed to address the complex geological characteristics of carbonate reservoirs, such as heterogeneity and lateral variations in gas layers. The well placement method is reasonable, which improves the reservoir drilling rate and achieves a leading domestic exploration and development drilling success rate of 92%. It enables high and stable production of single wells and can save a lot of money. Attached Figure Description

[0027] Figure 1 This is a flowchart of a well location deployment method for carbonate karst cave-fracture reservoirs according to the present invention;

[0028] Figure 2 This is a schematic diagram of the horizontal well pattern in the well placement area of ​​a carbonate karst cave-fracture reservoir well location deployment method according to the present invention. (a) is an effect diagram of the strong amplitude tower-shaped reflection type; (b) is an effect diagram of the strong amplitude discontinuous reflection type. Detailed Implementation

[0029] Combination Figure 1 and Figure 2 This embodiment describes a well location deployment method for carbonate karst cave-fracture reservoirs, which is implemented through the following steps:

[0030] Step 1: Based on the geological characteristics of interlayered karst carbonate reservoirs, the boundaries of oil and gas reservoirs are delineated using structural lines, fault lines, stratigraphic lines, physical property lines, and oil-water boundary lines, achieving a detailed interpretation of oil and gas reservoirs, structures, and faults; this is achieved through the following specific methods:

[0031] Step 11: Reprocess the seismic data volume and apply seismic-well logging combined wave impedance inversion technology, pre-stack fracture prediction technology and carbonate paleogeographic analysis technology to perform fracture interpretation and stratigraphic tracing.

[0032] Step 12: Based on core, well logging, and seismic data, the reservoir lithology, reservoir space type, degree of filling of fractured-vuggy reservoirs, and the variation of the degree of filling of fractured-vuggy reservoirs in the vertical and horizontal directions were analyzed.

[0033] Step 13: Combining static and dynamic data, based on single wells and with multi-well profile comparison, the longitudinal and lateral connectivity of the reservoir, inter-well connectivity, and oil-gas-water boundaries were studied.

[0034] Step 2: The prediction and description of special lithologies (rock types different from those of adjacent strata) are used as the basis for identifying marker layers during drilling. Geological sub-layer division, correlation, and reservoir prediction are then performed to define the reservoir's location and interlayers, thereby determining the reservoir's vertical development position. The specific methods are as follows:

[0035] Step 21: Divide the sub-layers according to lithology and cycle;

[0036] Step 22: Classification by composition: The high-gamma mudstone section is used as a marker layer during drilling.

[0037] Step 3: Classification and evaluation of reservoir seismic reflection types. Interlayer karst reservoirs are classified into "tower-like," "discontinuous," and "chaotic" reflection types; for example... Figure 2 As shown.

[0038] Tower-shaped reflection (cavity type): The production level is related to the size of the cavity. Large cavities (>20 channels, >4 strong peaks and valleys) produce more than 500,000 cubic meters of gas per day; medium cavities (10-20 channels, >4 strong peaks and valleys) produce more than 400,000 cubic meters of oil per day, and if located in a fractured area, the production can exceed 400,000 cubic meters per day; small cavities (<10 channels or 3-4 weak peaks and valleys) produce less than 300,000 cubic meters of oil per day, and if located in a fractured area, the production can exceed 300,000 cubic meters per day.

[0039] Intermittent reflections (formed by small karst caves): Oil production is related to the degree of fracture development; the more developed the fractures (simply look at the curvature of the cross-section), the higher the production; conversely, the less developed the fractures, the lower the production. Oil production in fractured areas exceeds 200,000 cubic meters per day, in less developed fractured areas it is 100,000-200,000 cubic meters per day, and in undeveloped fractured areas it is <100,000 cubic meters per day.

[0040] Disordered reflections: Low production, with oil production in fractured areas below 50,000 cubic meters per day.

[0041] Step 4: The interlayer karst reservoir is highly heterogeneous but has a quasi-layered distribution, which meets the conditions for horizontal well development. By applying the research of geostress field prediction and engineering geomechanics, the trajectory of the horizontal well is optimized, and the best trajectory direction is determined to be perpendicular to the maximum geostress or oblique at a large angle; the angle range is between 50 and 60 degrees.

[0042] Step 5: Layout the wells using a layout method that involves pilot wells and horizontal wells with horizontal sections of 1500-2000 meters in length, and ensuring that the well trajectory passes through "discontinuous" seismic reflections and passes through as many "tower-shaped" seismic reflections as possible.

[0043] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0044] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A well location deployment method for carbonate karst cave-fracture type reservoirs, characterized by: This method is implemented by the following steps: Step 1: Based on the geological characteristics of carbonate reservoirs, use structural lines, fault lines, stratigraphic lines, physical property lines, and oil-water boundary lines to delineate the boundaries of oil and gas reservoirs, thereby achieving a detailed interpretation of the reservoir structure and fractures. Step 2: Use the prediction and description of special lithology as the basis for identifying marker layers during drilling, and carry out geological sub-layer division, comparison and reservoir prediction to define the location and interlayers of interlayer karst reservoirs; Step 3: Based on the interlayer karst reservoirs described in Step 2, classify them according to reservoir seismic reflection type; these are divided into tower-shaped seismic reflection, discontinuous seismic reflection, and chaotic seismic reflection types. Step 4: Based on the distribution of the interlayer karst reservoir, optimize the horizontal well trajectory and determine the optimal horizontal well trajectory direction to be perpendicular to or at a large angle to the maximum geostress. Step 5: Well placement is carried out using a method where the horizontal section of the pilot well and horizontal well is 1500-2000 meters long, and the well trajectory passes through discontinuous seismic reflections and seismic tower-like reflections.

2. The well location deployment method for carbonate karst cave-fracture type reservoirs according to claim 1, characterized in that: The specific process of step one is as follows: Step 11: Processing the seismic data volume: Apply seismic-well logging combined impedance inversion technology, pre-stack fracture prediction technology, and carbonate paleogeographic analysis technology to perform fracture interpretation and stratigraphic tracing. Steps 1 and 2: Based on core, well logging, and seismic data, analyze reservoir lithology, reservoir space type, degree of filling of fractured-vuggy reservoirs, and the variation of the degree of filling of fractured-vuggy reservoirs in the vertical and horizontal directions. Step 13: Combining static and dynamic data, based on single wells and through multi-well profile comparison, study the vertical and horizontal connectivity of the reservoir, inter-well connectivity, and oil, gas and water boundaries to achieve a detailed interpretation of oil and gas reservoirs, structures and fractures.

3. The well location deployment method for carbonate karst cave-fracture type reservoirs according to claim 1, characterized in that: In step two, special lithology refers to rock types that differ from the lithology of adjacent strata.

4. The well location deployment method for carbonate karst cave-fracture type reservoirs according to claim 1, characterized in that: The specific process of step two is as follows: Step 21: Divide the geological sub-layers according to lithology and cycle. Step 22: Divide the geological sub-layers identified in Step 21 according to their composition, and use the high-gamma mudstone section as the marker layer during drilling.

5. The well location deployment method for carbonate karst cave-fracture type reservoirs according to claim 1, characterized in that: In step three, the tower-shaped seismic reflection type is the cave type: the output is related to the size of the cave; it is divided into large caves, medium caves and small caves.

6. The well location deployment method for carbonate karst cave-fracture type reservoirs according to claim 5, characterized in that: The discontinuous seismic reflection type is formed by the connection of small karst caves, and the production level is related to the degree of crack development.

7. A well location deployment method for carbonate karst cave-fracture type reservoirs according to claim 6, characterized in that: The more developed the fractures, the higher the oil production; conversely, the less developed the fractures, the lower the production. Oil production in fracture-developed areas exceeds 200,000 cubic meters per day, while production in less developed fracture areas is between 100,000 and 200,000 cubic meters per day. In areas with minimal fracture development, the oil production is... <100,000 cubic meters / day.

8. The well location deployment method for carbonate karst cave-fracture type reservoirs according to claim 1, characterized in that: Disordered seismic reflection type: low production, with oil production in fracture-developed areas below 50,000 cubic meters per day.

9. A well location deployment method for carbonate karst cave-fracture type reservoirs according to claim 1, characterized in that: In step four, the interlayered karst reservoir is distributed in a quasi-layered manner, and the horizontal well trajectory is optimized by using geostress field prediction and engineering geomechanics.

10. A well location deployment method for carbonate karst cave-fracture type reservoirs according to claim 1, characterized in that: In step four, the optimal horizontal well trajectory direction is determined to be perpendicular to or at a large angle to the maximum ground stress, with the large angle ranging from 50 to 60 degrees.

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