A method for selecting reservoir stimulation horizons by following fractures and finding holes

Abstract

A method for selecting reservoir stimulation horizons by following fractures and finding cavities, comprising the following steps: Step 1, collect existing single-well logging data, seismic data, and relevant previous construction and production data of fractured-vuggy reservoir; Step 2, quantitatively understand the distribution characteristics of fractures and cavities within the block using statistical analysis methods, compare with the previous construction and production data, and correct the areas with large deviations to obtain the statistical analysis results; Step 3, combine the statistical analysis results and the seismic data, construct a three-dimensional geological model of fracture and cavity distribution in geological modeling software, and perform single-well stress field calculation and verification; Step 4, use the three-dimensional geological model to simulate the formation of a connection network of wellbore - fractures - cavities in AiFrac fracturing simulation software, screen out the horizons where the main branch fractures or natural fractures are more developed in the formation after acid fracturing, and finally select the reservoir stimulation horizons with the goal of maximizing the communication between acid fracturing fractures and cavity reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of the development of fractured-vuggy reservoirs, and particularly relates to a method for selecting reservoir stimulation horizons by following fractures to find vugs. Background Art

[0002] Carbonate fractured-vuggy reservoirs are widely distributed at home and abroad and have rich reserves. However, due to their special type, not only are the lithologies dense, the matrix is oil-free, and pores, fractures and vugs are developed, but also the spatial combination forms of the main oil and gas reservoirs are complex and diverse, and the scales vary greatly. Development practices have confirmed that the main production and injection units of fractured-vuggy reservoirs are composed of fractured-vug units with different numbers and reserve scales.

[0003] The existing methods for selecting reservoir stimulation horizons are generally used for coalbed methane wells or shale. For example, the invention patent with the application number 201711447492.9 discloses a method for optimizing fracturing horizons of coalbed methane wells, and the invention patent with the application number 201811194735.7 discloses a method for optimizing the fracturable horizons of shale in tight oil horizontal wells. The technologies proposed in the above two invention patents do not involve the efficient communication of natural fractures and vug reservoirs on which fractured-vuggy reservoirs rely, so they are not applicable to the selection of reservoir stimulation horizons for fractured-vuggy reservoirs. Therefore, it is necessary to establish a method for selecting reservoir stimulation horizons for fractured-vuggy reservoirs based on following fractures to find vugs. Summary of the Invention

[0004] The present invention provides a method for selecting reservoir stimulation horizons by following fractures to find vugs. A three-dimensional geological model of fracture and vug distribution is constructed by using geological modeling software, and a method for selecting reservoir stimulation horizons for efficient development of fractured-vuggy reservoirs is proposed under the guidance of the technical idea of following fractures to find vugs by constructing channels connecting the wellbores with the fractures and vugs based on the spatial distribution conditions of fractures and vugs.

[0005] The technical solution of the present invention is as follows:

[0006] A method for selecting reservoir stimulation horizons by following fractures to find vugs, characterized by comprising the following steps:

[0007] S1, collecting the existing single-well logging data, seismic data, and relevant previous construction and production data in the reservoir of the carbonate fractured-vuggy reservoir;

[0008] S2, quantitatively understanding the distribution characteristics of natural fractures and vugs in the reservoir by using statistical analysis methods according to the single-well logging data and seismic data, and comparing with the previous construction and production data to correct the areas with large deviations, so as to obtain the statistical analysis results;

[0009] S3, combining the statistical analysis results and the seismic data, constructing a three-dimensional geological model of single-well fracture and vug distribution in geological modeling software, and performing single-well stress field calculation and verification;

[0010] S4. Based on the technical idea of "tracking fissures to find cavities", a three-dimensional geological model of the single-well fissure-cavity distribution is used to simulate the formation of a connection network of wellbore - fissures - cavities in the fracturing and acidizing simulation software. The layers with well-developed main branch fissures or natural fissures in the formation after acid fracturing are screened out. With the goal of maximizing the communication between acid-fracture and cavity reservoirs, the layers for reservoir stimulation are finally selected.

[0011] Preferably, in S3, the specific steps for constructing the three-dimensional geological model of fissure-cavity distribution and calculating and verifying the single-well stress field are as follows:

[0012] S3.1 Combining seismic data, the ant tracking technology is used to obtain the distribution characteristics of natural fissures and assign them to the geological modeling software in the form of natural fissure parameters, thereby establishing a three-dimensional geological model of natural fissure distribution.

[0013] S3.2 Combining the seismic data, the root mean square amplitude algorithm is used to extract the distribution characteristics of cavities, and the cavity distribution characteristics are assigned to the three-dimensional geological model of natural fissure distribution in the form of cavity parameters, forming a three-dimensional geological model of fissure-cavity distribution.

[0014] S3.3 Combining the single-well logging data, logging information is extracted and assigned to the three-dimensional geological model of fissure-cavity distribution in the form of logging parameters, forming a three-dimensional geological model of single-well fissure-cavity distribution.

[0015] S3.4 Combining the statistical analysis results, the single-well stress is calculated using the three-dimensional geological model of single-well fissure-cavity distribution and compared with the measured single-well stress data. If the error is within 5%, the three-dimensional geological model of single-well fissure-cavity distribution is a better model; otherwise, the natural fissure parameters and / or cavity parameters and / or logging parameters of the three-dimensional geological model of single-well fissure-cavity distribution are adjusted to make the error within 5%.

[0016] Preferably, in S4, based on the technical idea of "tracking fissures to find cavities", the specific content of using the three-dimensional geological model to simulate the formation of a connection network of wellbore - fissures - cavities in the fracturing and acidizing simulation software is as follows: For cavity reservoirs within a certain range around the wellbore, by injecting acid fluid into the wellbore, the acid fluid flows along natural fissures or high-permeability zones. Without being controlled by in-situ stress, the acid fluid follows natural fissures or high-permeability zones to communicate with cavity reservoirs in different directions, thereby achieving the connection of such cavity reservoirs with the wellbore through multiple channels in all directions, that is, forming a connection network of wellbore - fissures - cavities and realizing the efficient exploitation of cavity reservoirs.

[0017] Preferably, the logging data includes but is not limited to imaging logging data, natural gamma logging data, caliper logging data, and density logging data.

[0018] Preferably, the relevant construction and production data include, but are not limited to, pre - well acid fracturing construction data, post - fracturing evaluation data, and well production.

[0019] Preferably, the natural fracture distribution characteristics include the natural fracture density, natural fracture length range, natural fracture width range, natural fracture height range, natural fracture strike range, and natural fracture dip range obtained through well logging data and seismic profile data analysis.

[0020] Preferably, the karst cave distribution characteristics include the volume range of karst caves, karst cave distribution range, and karst cave connectivity obtained through well logging data and seismic profile data analysis.

[0021] Preferably, the acid fracturing simulation software includes AiFrac acid fracturing simulation software.

[0022] The advantages of the present invention over the prior art are as follows: The method for selecting reservoir reconstruction horizons of finding caves along fractures in the present invention utilizes the existing single - well logging data, seismic data, and relevant construction and production data of fracture - cave type reservoirs to construct a three - dimensional geological model of single - well fracture - cave distribution in geological modeling software, and perform single - well stress field calculation and verification; and proposes to construct a channel connecting the wellbore and karst caves under the condition of the spatial distribution of fractures and caves, guided by the idea of finding caves along fractures, that is, using the three - dimensional geological model of single - well fracture - cave distribution to simulate and form a connection network of wellbore - fracture - karst cave in acid fracturing simulation software, screening out the horizons where the main branch fractures or natural fractures are more developed in the formation after acid fracturing, and aiming at maximizing the communication between acid - fracturing fractures and karst cave reservoirs, finally selecting the horizons for reservoir reconstruction. This method is applicable to the selection of reservoir reconstruction horizons for the efficient development of fracture - cave type reservoirs, making up for the lack of methods for selecting reservoir reconstruction horizons in fracture - cave type reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the method for selecting reservoir reconstruction horizons of finding caves along fractures in the present invention;

[0024] Figure 2 show the natural fractures and karst caves interpreted from well logging data in the method for selecting reservoir reconstruction horizons of finding caves along fractures in the present invention. The fracture - cave display characteristics are that the natural gamma shows high values, the resistivity curve shows a saw - tooth oscillation feature, and the porosity and permeability increase significantly;

[0025] Figure 3 show the karst caves interpreted from seismic data in the method for selecting reservoir reconstruction horizons of finding caves along fractures in the present invention. The characteristics are that on the paleogeomorphology, it shows as circular depressions, the seismic event groups are offset downward, and the anomalies are scattered and linear along the underground river.

[0026] Figure 4It is the three-dimensional geological model of natural fracture distribution simulated in the reservoir reconstruction horizon selection method of finding holes along fractures of the present invention;

[0027] Figure 5 It is the three-dimensional geological model of karst cave distribution in the three-dimensional geological model of fracture-cave distribution simulated in the reservoir reconstruction horizon selection method of finding holes along fractures of the present invention;

[0028] Figure 6 It is the calculation result of the in-situ stress field of the three-dimensional geological model of single-well fracture-karst cave distribution simulated in the reservoir reconstruction horizon selection method of finding holes along fractures of the present invention;

[0029] Figure 7 It is the calculation result of acid fracturing fracture communication simulated by using the AiFrac fracturing simulation software for vertical wells in the reservoir reconstruction horizon selection method of finding holes along fractures of the present invention;

[0030] Figure 8 It is the calculation result of acid fracturing fracture communication simulated by using the AiFrac fracturing simulation software for deviated wells in the reservoir reconstruction horizon selection method of finding holes along fractures of the present invention;

[0031] Figure 9 It is the calculation result of acid fracturing fracture communication simulated by using the AiFrac fracturing simulation software for horizontal wells in the reservoir reconstruction horizon selection method of finding holes along fractures of the present invention. Detailed implementation manners

[0032] For the convenience of understanding the present invention, the present invention will be described in more detail below in conjunction with specific embodiments.

[0033] The method for selecting a reservoir reconstruction horizon for finding holes along fractures, the flow chart of which is as Figure 1 shown, includes the following steps:

[0034] S1. Collect the existing single-well logging data, seismic data, and relevant previous construction and production data in the fractured-vuggy carbonate reservoir; the relevant construction and production data include but are not limited to the previous oil well acid fracturing construction data, post-fracture evaluation data, and oil well production; the logging data includes but is not limited to imaging logging data, natural gamma logging data, well diameter logging data, and density logging data;

[0035] S2. According to the single-well logging data and seismic data, use statistical analysis methods to quantitatively understand the distribution characteristics of natural fractures (as Figure 2 shown) and the distribution characteristics of karst caves (as Figure 3as shown in the figure), and compare it with the previous construction production data, correct the areas with large deviations, and obtain the statistical analysis results; among them, the natural fracture distribution characteristics include the natural fracture density, natural fracture length range, natural fracture width range, natural fracture height range, natural fracture strike range, and natural fracture dip range obtained through well logging data and seismic profile data analysis; the karst cave distribution characteristics include the volume range of karst caves, karst cave distribution range, and karst cave connectivity obtained through well logging data and seismic profile data analysis;

[0036] S3. Combine the statistical analysis results and the seismic data, and construct a 3D geological model of single-well fracture and karst cave distribution in the geological modeling software, and perform single-well stress field calculation and verification; specifically:

[0037] S3.1 Combine the seismic data, adopt the ant tracking technology, obtain the natural fracture distribution characteristics and assign them to the geological modeling software in the form of natural fracture parameters, and establish a 3D geological model of natural fracture distribution as shown in the figure; Figure 4 as shown in the figure;

[0038] S3.2 Combine the seismic data, adopt the root mean square amplitude algorithm, extract the karst cave distribution characteristics, and assign the karst cave distribution characteristics to the 3D geological model of natural fracture distribution in the form of karst cave parameters to form a 3D geological model of fracture and karst cave distribution as shown in the figure; Figure 5 as shown in the figure;

[0039] S3.3 Combine the single-well well logging data, extract the well logging information, and assign the well logging information to the 3D geological model of fracture and karst cave distribution in the form of well logging parameters to form a 3D geological model of single-well fracture and karst cave distribution;

[0040] S3.4 Combine the statistical analysis results, use the 3D geological model of single-well fracture and karst cave distribution to calculate the single-well stress, and compare the calculation result of the in-situ stress field of the 3D geological model of single-well fracture and karst cave distribution with the measured single-well stress data. If the error is within 5%, then the 3D geological model of single-well fracture and karst cave distribution is a better 3D geological model of single-well fracture and karst cave distribution.

[0041] S4. Based on the idea of the technology of finding karst caves along fractures, for the karst cave reservoir bodies within a certain range around the wellbore, by injecting acid fluid at the injection point of the wellbore, the acid fluid flows along the natural fractures or high-permeability zones. Without being controlled by the in-situ stress, the acid fluid follows the natural fractures or high-permeability zones to communicate with the karst cave reservoir bodies in different directions, so as to realize the connection of this type of karst cave reservoir bodies with the wellbore through multiple channels in various directions. Specifically, extract the fracture and karst cave distribution information of different layers of the oil well W in the 3D geological model of single-well fracture and karst cave distribution, and use the AiFrac fracturing simulation software to perform the simulation calculation of acid fracturing to communicate with the karst caves. Before the calculation, according to the stress field simulated by the stress field simulation, as shown in the figure Figure 6As shown, the vertical in-situ stress is 170 MPa, the maximum horizontal in-situ stress is 140 MPa, and the minimum horizontal in-situ stress is 120 MPa, and the initial stress conditions for fracturing simulation are set. Based on the idea of the technique of searching for cavities along fractures, in this embodiment, simulation calculations are respectively carried out for vertical wells, deviated wells, and horizontal wells: As Figure 7 Shown is the simulation calculation of acid fracturing to communicate with karst caves in a vertical well using the AiFrac fracturing simulation software. After the acid fracturing cracks activate the natural fractures, the karst cave reservoirs are communicated, that is, the layer where the reservoir is located is the preferred layer for acid fracturing transformation;

[0042] As Figure 8 Shown is a deviated well. The simulation calculation of acid fracturing to communicate with karst caves is carried out using the AiFrac fracturing simulation software. The acid fracturing cracks communicate with two karst cave reservoirs at layer II, that is, layer II is the preferred layer for acid fracturing transformation of this well;

[0043] As Figure 9 Shown is the simulation calculation of acid fracturing to communicate with karst caves in a horizontal well using the AiFrac fracturing simulation software. The acid fracturing cracks communicate with one karst cave reservoir at layer I, two karst cave reservoirs at layer II, one karst cave reservoir at layer III, and one karst cave reservoir at layer VI. That is, the communication degree of the karst cave reservoirs at layer II is the largest, followed by layers I, III, and VI. This horizontal well preferentially selects layer II for acid fracturing transformation.

[0044] It should be noted that the above specific embodiments can enable those skilled in the art to understand the present invention more comprehensively, but do not limit the present invention in any way. Therefore, although this specification has described the present invention in detail with reference to the drawings and embodiments, those skilled in the art should understand that the present invention can still be modified or equivalently replaced. In short, all technical solutions and their changes that do not depart from the spirit and scope of the present invention should be covered by the protection scope of this invention patent.

Claims

1. A method for selecting reservoir stimulation horizons by following seams and finding holes, characterized in that It includes the following steps: S1. Collect the existing single-well logging data, seismic data, and relevant previous construction and production data in the fractured-vuggy carbonate reservoir. S2. According to the single-well logging data and seismic data, use statistical analysis methods to quantitatively understand the distribution characteristics of natural fractures and vugs in the reservoir, and compare with the previous construction and production data to correct the deviated areas and obtain the statistical analysis results. S3. Combine the statistical analysis results and the seismic data to construct a three-dimensional geological model of single-well fracture-vug distribution in geological modeling software, and perform single-well stress field calculation and verification, which specifically includes the following steps: S3.1 Combine the seismic data and use the ant tracking technology to obtain the distribution characteristics of the natural fractures and assign them to the geological modeling software in the form of natural fracture parameters to establish a three-dimensional geological model of natural fracture distribution. S3.2 Combine the seismic data and use the root mean square amplitude algorithm to extract the distribution characteristics of the vugs, and assign the distribution characteristics of the vugs to the three-dimensional geological model of natural fracture distribution in the form of vug parameters to form a three-dimensional geological model of fracture-vug distribution. S3.3 Combine the single-well logging data, extract the logging information, and assign the logging information to the three-dimensional geological model of fracture-vug distribution in the form of logging parameters to form a three-dimensional geological model of single-well fracture-vug distribution. S3.4 Combine the statistical analysis results, use the three-dimensional geological model of single-well fracture-vug distribution to calculate the single-well stress field, and compare it with the measured single-well stress data. If the error is within 5%, the three-dimensional geological model of single-well fracture-vug distribution is an acceptable three-dimensional geological model of single-well fracture-vug distribution; otherwise, adjust the natural fracture parameters and / or vug parameters and / or logging parameters of the three-dimensional geological model of single-well fracture-vug distribution to make the error within 5%. S4. Based on the idea of following fractures to find vugs, use the three-dimensional geological model of single-well fracture-vug distribution to simulate and form a connection network of wellbore - fracture - vug in the acid fracturing simulation software, screen out the layers with well-developed main branch fractures or natural fractures in the formation after acid fracturing, and aim at maximizing the communication between acid fracturing fractures and vug reservoirs, and finally select the layers for reservoir stimulation. The specific content is as follows: For the vug reservoirs within the selected range around the wellbore, by injecting acid fluid into the wellbore, the acid fluid flows along the natural fractures or high-permeability zones. Without being controlled by in-situ stress, the acid fluid follows the natural fractures or high-permeability zones to communicate with the vug reservoirs in different directions, thereby realizing the connection of the vug reservoirs with the wellbore through multiple channels in all directions, that is, forming a connection network of wellbore - fracture - vug and achieving efficient exploitation of the vug reservoirs.

2. The method for selecting reservoir reconstruction horizons by following seams and finding holes according to claim 1, characterized in that The single-well logging data includes imaging logging data, natural gamma logging data, caliper logging data, and density logging data.

3. The method for selecting a reservoir reconstruction horizon for seam-tracing and hole-finding according to claim 1, characterized in that, The previous construction and production data includes previous oil well acid fracturing construction data, post-fracture evaluation data, and oil well production.

4. The method for selecting a reservoir reconstruction horizon for seam tracing and hole finding according to claim 1, characterized in that The acid fracturing simulation software includes AiFrac fracturing simulation software.

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