Method for determining shale oil platform fracturing artificial fracture parameter observation coring well group

Abstract

The invention discloses a shale oil platform fracturing artificial fracture parameter observation coring well group determination method. The method comprises the steps that 1, an observation platform is selected; 2, an observation horizontal well is selected; 3, fracturing parameters are set; 4, the seam length and the seam height of the horizontal well are observed and monitored; 5, a coring well group is designed; and 6, a shale oil large platform well pattern is arranged. The method provided by the invention has the characteristics of multi-well reference and reliable result, effectively solves the problem that parameters such as fracturing artificial fracture length and fracture height cannot be clearly known, can quantitatively and intuitively count the hydraulic fracturing artificial fracture propagation parameters of Chinese continental facies multi-type shale oil reservoirs in different fracturing modes, and has the advantages of high accuracy and high reliability. Key support is provided for shale oil large platform well pattern optimization and fracturing design, and the development process of continental facies shale oil is powerfully promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of oil field development and relates to a method for determining a coring well group for observation of artificial fracture parameters of a shale oil platform fracturing. Background Art

[0002] Downhole microseismicity is currently the most mainstream hydraulic fracturing fracture parameter acquisition and testing technology. Microseismicity monitors the signal of the fracturing wave. The actual fracture height and length are much smaller than the distribution range of the microseismic event. The spacing of horizontal wells on large platforms refers to the microseismic fracture length. Artificial fractures are not enough to achieve full coverage of inter-well reserves. The utilization of shale oil inter-well reserves is limited, and the transformation efficiency has not been maximized. The thickness of the three-dimensional development interlayer refers to the microseismic fracture height. Artificial fractures are not enough to achieve full utilization of the vertical multi-layer sweet spot, and the utilization of vertical reserves is limited; reducing the well spacing based on microseismicity is likely to cause inter-well pressure channeling, resulting in increased water content, and it is difficult to increase the production of a single well; the specific parameters of artificial fractures under different transformation modes such as single-stage single cluster, multiple-stage few clusters, and large-stage multiple clusters are unknown, and it is difficult to evaluate the transformation methods and transformation effects suitable for different shale oil reservoirs. Domestic related oil fields have attempted to observe hydraulic fractures downhole, but no fractures were observed due to inappropriate design. Although coring observations of fractures have been achieved in North America through coring, a coring well group design method for quantitative statistics of fracture length, height and width has not been formed.

[0003] Shale oil has become a huge pillar to ensure the stable production of more than 200 million tons of crude oil in China. Clarifying the key parameters of hydraulic fracture network is of great significance to promoting the efficient development of continental shale oil. Therefore, it is urgent to develop a method for observing and coring well groups of artificial fracture parameters of shale oil platform fracturing, so as to provide an effective reference for the deployment of horizontal wells using the same development method for low permeability oil and gas reservoirs and shale gas. Summary of the invention

[0004] The purpose of the present invention is to provide a method for determining a coring well group for observation of parameters of artificial fractures in a shale oil platform, which solves the problem in the prior art that it is difficult to achieve quantitative statistics of fracture length, fracture height and fracture width in coring observation of fractures.

[0005] The technical solution adopted by the present invention is a method for determining a coring well group for observation of artificial fracture parameters of a shale oil platform fracturing, which is implemented according to the following steps:

[0006] Step 1: Select the observation platform;

[0007] Step 2, selecting an observation horizontal well;

[0008] Step 3, setting fracturing parameters;

[0009] Step 4: Observe the fracture length and fracture height of the horizontal well and monitor them;

[0010] Step 5: Design the coring well group;

[0011] Step 6: Set up the shale oil platform well network.

[0012] The beneficial effect of the present invention is that, by designing a coring well group for hydraulic fracturing horizontal wells, and by designing key steps such as typical platform selection, observation horizontal well selection, fracturing parameter design, fracture test design, and coring well group design, a coring well group design method for quantitative statistics of hydraulic fracturing artificial fracture network parameters is determined, which has the characteristics of multi-well reference and reliable results, and effectively solves the problem of unclear understanding of parameters such as fracturing artificial fracture length and fracture height. The use of this technical means can quantitatively and intuitively count the hydraulic fracturing artificial fracture expansion parameters of China's continental multi-type shale oil reservoirs under different fracturing modes, providing key support for the optimization of shale oil large platform well network and fracturing design, and effectively promoting the continental shale oil revolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1a This is a schematic diagram 1 of the design of a horizontal well group for fracture height observation according to Embodiment 1 of the present invention;

[0014] Figure 1b This is a second schematic diagram of the design of a horizontal well group for fracture height observation according to Embodiment 1 of the present invention;

[0015] Figure 2a This is a schematic diagram 1 of the design of a horizontal well group for fracture length observation according to Example 1 of the present invention;

[0016] Figure 2b This is a second schematic diagram of the design of a horizontal well group for fracture length observation according to Embodiment 1 of the present invention;

[0017] Figure 3 This is a platform fracture analysis diagram of H41 in Example 2 of the present invention;

[0018] Figure 4 This is a geological quality analysis diagram of the H41-4 well in Example 2 of the present invention;

[0019] Figure 5a It is a plan view of the sand body thickness of the QH41 platform length 71 of Example 2 of the present invention;

[0020] Figure 5b is a plane diagram of oil saturation of the QH41 platform length 71 of Example 2 of the present invention;

[0021] Figure 5c is a porosity plane diagram of a QH41 platform length 71 of Example 2 of the present invention;

[0022] Figure 5d is a plane diagram of the brittleness coefficient of the QH41 platform length 71 of Example 2 of the present invention;

[0023] Figure 6 is a three-dimensional schematic diagram of the QH41 observation well in Example 2 of the present invention;

[0024] Figure 7a This is a fracturing design diagram of a longitudinal fracture height observation well according to Example 2 of the present invention;

[0025] Figure 7b This is a fracturing design diagram of a plane fracture length observation well according to Example 2 of the present invention;

[0026] Figure 8a This is a fracture height statistics diagram of the stacked microseismic monitoring of the Qing H41-3 well in Example 2 of the present invention;

[0027] Figure 8b This is a statistical diagram of microseismic fracture length parameters of the Qing H41-3 well in Example 2 of the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] The method of the present invention realizes quantitative statistics of key parameters such as artificial fracture length and fracture height through precise design of the coring well group, and is implemented according to the following steps:

[0030] Step 1: Select the observation platform.

[0031] In order to ensure the representativeness of coring observation, the selection of observation platform needs to meet the following five principles: ① The oil layer heterogeneity within 300m of the root of the horizontal well is weak, and the plane and vertical distribution are stable; ② There is basically no development of faults in the observation platform range, and there are no large faults or cracks communicating vertically and horizontally; ③ The orientation of horizontal wells on the observation platform is perpendicular to the maximum principal stress, and the number of wells is greater than four; ④ The observation platform does not belong to the development overlap area; ⑤ No blowout, overflow or other events occur during the drilling process of the observation platform, and the cementing quality at the root of the horizontal well is qualified.

[0032] Step 2: Select the horizontal well for observation.

[0033] At least two or more horizontal wells are selected inside the observation platform as key observation horizontal wells, of which at least one is mainly used to monitor the longitudinal fracture height, and at least another is mainly used to monitor the plane fracture length. The two wells verify each other to ensure the accuracy of fracture parameter acquisition; through three-dimensional geological modeling and mechanical modeling, it is ensured that the reservoir thickness of the selected observation horizontal wells within 500m on both sides of the root (or left and right directions) is stable, the brittleness coefficient is similar, and the stress difference on both sides is small.

[0034] Step 3: Set the fracturing parameters.

[0035] The root of the horizontal well adopts three fracturing modes: single-stage single cluster, multi-stage few clusters and large-stage multiple clusters. Each fracturing mode has at least two, and they are separated. Different fracturing modes are supported by proppants of different colors to facilitate the distinction of fracture heights of different fracturing modes.

[0036] At the same time, the root of the horizontal well for plane fracture length observation is designed separately in one of the three modes: single-segment single cluster, multiple-segment few clusters, and large-segment multiple clusters (other modes can increase observation horizontal wells separately), and the number of designed segments is at least greater than eight to ensure the accuracy of the fracture length parameters; since the two observation horizontal wells are adjacent, the proppant of this well is not dyed in order to distinguish the fractures.

[0037] Step 4: Observe the fracture length and fracture height of the horizontal well and monitor it.

[0038] For key observation horizontal wells, downhole microseismic or sonar remote fracture monitoring technology is used to obtain key fracture test parameters of fracture length and fracture height of key observation horizontal wells; at the same time, by conducting downhole television hole erosion monitoring on the observation horizontal wells, it is ensured that the opening rate of each cluster in the root fracturing design section of the observation horizontal well is >80%, ensuring that the hydraulic fracturing transformation effect is obvious.

[0039] Step 5: Design the coring well group. The specific process is:

[0040] 5.1) Set up a horizontal well group for vertical fracture height observation.

[0041] A total of four vertical fracture height monitoring coring wells were designed, including two high-angle coring wells and two horizontal wells. Figure 1a , Figure 1b ,

[0042] First, two highly deviated coring wells were implemented. The plane projection of the highly deviated coring wells was parallel to the observation horizontal well, and the plane distance from the observation horizontal well was less than 10% of the half-fracture length of the fracture test. The two highly deviated coring wells were symmetrical around the observation horizontal well (X1, X2). Well X1 cored from the top of the reservoir to the bottom, and well X2 cored from the bottom of the reservoir to the top of the formation. The vertical distance of the two wells passing through the reservoir must be greater than the average value of the upper fracture height of the fracture test reservoir; the vertical distance of the two wells passing through the reservoir must be greater than the average value of the lower fracture height of the fracture test reservoir, and the microseismic event points in the coring section were active.

[0043] Then, based on the observation of artificial fractures in two highly deviated coring wells, two horizontal coring wells (P1 and P2) are symmetrically arranged around the observation horizontal well. The distance between the horizontal coring well and the observation horizontal well is 1 / 2 of the well distance between the highly deviated coring well and the observation horizontal well. The P1 well is located above the reservoir, and the coring direction is the line connecting the highest points O1→O2 of the artificial fracture coring observations in the two highly deviated coring wells; the P2 well is located below the reservoir, and the coring direction is the line connecting the highest points O3→O4 of the artificial fracture coring observations in the two highly deviated coring wells. See Example 1. Figure 1a , Figure 1b ;

[0044] The vertical distances from the artificial fractures observable in the cores of wells P1 and P2 to the middle of the oil layer were counted, and their average values ​​were taken as the actual upper fracture height and lower fracture height of the fracturing.

[0045] 5.2) Set up a horizontal well group for plane fracture length observation.

[0046] A total of four horizontal coring wells are arranged in the horizontal well group for plane fracture length observation. Figure 2a , Figure 2b ;

[0047] First, two horizontal coring wells, B1 and B2, were implemented. The minimum distance between the two horizontal coring wells B1 and B2 and the fracture length observation horizontal well was less than 10% of the half fracture length of the fracture test, and the maximum distance was the average value of the half fracture length. One well was cored from the observation horizontal well from near to far, and the other well was cored from the observation horizontal well from far to near.

[0048] Then obtain the maximum half-fracture length points O5 and O6 of the artificial fracture core observation of the two horizontal core wells B1 and B2, and set two more core wells B3 and B4 in the direction of the O5-O6 connection line and in the direction symmetrical around the observation horizontal well;

[0049] Then, the vertical distances of all artificial fractures observed in the two core wells B3 and B4 from the observation horizontal wells were counted, and their average values ​​were taken as the left and right half fracture lengths of the artificial fractures.

[0050] Step 6: Set up the shale oil platform well network.

[0051] According to the half-fracture length and fracture height data obtained in step 5, the horizontal well spacing of the single-layer shale oil platform is greater than or equal to the fracture length statistically calculated by the coring well group (not exceeding 10% of the statistical value), and the thickness of the longitudinal interlayer of the three-dimensional development platform is greater than or equal to the fracture height statistically calculated by the coring well group (not exceeding 10% of the statistical value). Based on this, the shale oil platform well network is set up.

[0052] Example 1

[0053] The steps of Example 1 refer to the aforementioned method, and the parameters involved and the corresponding results have been described along with the steps. The results show that the method of the present invention can be reliably implemented and the results are accurate.

[0054] Example 2

[0055] PetroChina Changqing Oilfield has started the construction of the first shale oil hydraulic fracturing test site in China. Through coring wells, artificial fractures have been re-recognized, providing references for optimizing well spacing, segment cluster design, fracturing sequence and research on improving recovery, and promoting the upgrading of unconventional oil and gas development technology. The specific process is as follows:

[0056] 1) Select an observation platform,

[0057] Using the Qing H41 platform, the fault was analyzed through 3D seismic interpretation (see Figure 3 ), the maximum principal stress of the horizontal well deployment azimuth vertically, the number of platform deployment wells 5 meets the requirements, and it does not belong to the development overlap area. The geological quality analysis shows that the root of the horizontal well is a three-dimensional sweet spot distribution area (see Figure 4 ), meeting the basic selection principles of the observation platform.

[0058] 2) Select the horizontal well for observation,

[0059] Through 3D geological modeling, the reservoir thickness within 500m on both sides of the root of the selected observation horizontal well H41 is stable, the brittleness coefficient is similar, and the stress difference on both sides is small (see Figure 5a , Figure 5b , Figure 5c , Figure 5d ). Two adjacent wells were selected as observation wells, and the distribution was used as horizontal wells for fracture height and fracture length observation. Since the focus of coring this time was to observe the fracturing effect, the quantitative parameters of the well pattern were not obtained according to the well group design in this test site, but the idea of ​​selecting the observation platform and the observation horizontal well was consistent.

[0060] 3) Set fracturing parameters,

[0061] Well H41-3 is a horizontal well for vertical fracture height observation. Three fracturing modes are used at the root: single-stage single cluster, multi-stage few clusters, and large-stage multiple clusters. Each fracturing mode has at least two, and they are separated. Different fracturing modes are supported by proppants of different colors to facilitate the distinction of fracture heights of different fracturing modes.

[0062] Well H41-4 is a horizontal well for plane fracture length observation. The root is designed with a multi-stage and few-cluster mode. In order to distinguish fractures, the proppant of this well is not dyed (see Figure 7a , Figure 7b ).

[0063] 4) Conduct crack test,

[0064] The qualitative data of fracture length and height obtained through microseismic analysis is used as the basis for core well design ( Figure 8a , Figure 8b ).

[0065] 5) Set up the coring well group,

[0066] Since the focus of this coring is to observe the fracturing effect, the test site did not obtain the quantitative parameters of the well pattern according to the well group design, but referred to the coring well group design idea. According to the design of the high-angle coring well parallel to Q41-3, the average seismic half-fracture length is 300m, the high-angle distance is 30m from the horizontal well, and the minimum distance between the horizontal coring well and the Q41-4 well is 30m, and they are set from near to far (see Figure 6 ). At present, the fracturing sand has been observed in the high-angle coring wells according to the design, and the actual fracture height under single-stage single-cluster fracturing has been monitored. This shows that the method of the present invention is in line with the design idea of ​​quantitative acquisition of fracture parameters. The well pattern parameters obtained by the method of the present invention can effectively improve the reserve utilization degree and single well production, providing support for shale oil production increase.

[0067] Example 3

[0068] In the early stage, coring was carried out at the YP well site to observe the fracturing. Based on the microseismic analysis, coring was started at a position 170m away from the YP3 well and 140m away from the YP4 well. A total of 141.95m of coring was carried out in the long 7th section of the longitudinal continuous coring, and no fracturing was observed. The main reason is that the distance between the coring well and the fracturing well should not be too long. Therefore, the fracture length monitoring well must be cored from the target well from near to far to ensure that the fracturing can be observed. The Q41-4 well was designed using this method, and the fracturing was observed, achieving the purpose of quantitatively counting the half-fracture length. This shows that the method of the present invention is in line with the design idea of ​​quantitative acquisition of fracture parameters.

[0069] Example 4

[0070] In the early stage, in the An 239-24 well (directional well), the plane distance was 80m, located in the middle and upper part of the oil layer. The core was taken at 85m within the microseismic coverage range, and no support fractures were found. This shows that there are not necessarily hydraulic fractures in places where microseismic events are dense, and the fracture height monitoring well must be closer to the observation well. The Q41-3 well was designed using this method. The core was taken at 30m away from the horizontal well, and hydraulic fractures were observed. This shows that the method of the present invention is in line with the design idea of ​​quantitative acquisition of fracture parameters.

Claims

1. A method for determining a coring well group for observation of artificial fracture parameters in a shale oil platform fracturing, characterized in that: Follow these steps to implement: Step 1: Select the observation platform; Step 2, selecting an observation horizontal well; Step 3, setting fracturing parameters; Step 4: Observe the fracture length and fracture height of the horizontal well and monitor them; Step 5: Design the coring well group; Step 6: Set up the shale oil platform well network.

2. The method for determining the coring well group for observation of artificial fracture parameters of shale oil platform fracturing according to claim 1 is characterized in that: In step 1, the selection of the observation platform needs to meet the following five principles: ① The oil layer heterogeneity within 300m of the horizontal well root is weak, and the horizontal and vertical distribution is stable; ② There is basically no development of faults in the observation platform range, and there are no large faults or fractures communicating vertically and horizontally; ③ The orientation of the horizontal wells on the observation platform is perpendicular to the maximum principal stress, and the number of wells is greater than four; ④ The observation platform does not belong to the development overlap area; ⑤ No blowout or overflow incidents occurred during the drilling process of the observation platform, and the cementing quality at the root of the horizontal well was qualified.

3. The method for determining the coring well group for observation of artificial fracture parameters of shale oil platform fracturing according to claim 1, characterized in that: In step 2, the specific process is: At least two horizontal wells are selected inside the observation platform as key observation horizontal wells, of which at least one is mainly used to monitor the vertical fracture height, and at least the other is mainly used to monitor the plane fracture length. Through three-dimensional geological modeling and mechanical modeling, it is ensured that the reservoir thickness within 500m on both sides of the root of the selected observation horizontal wells is stable, the brittleness coefficient is similar, and the stress difference on both sides is small.

4. The method for determining the coring well group for observation of artificial fracture parameters of shale oil platform fracturing according to claim 1, characterized in that: In step 3, the specific process is: The root of the horizontal well for vertical fracture height observation adopts three fracturing modes: single-stage single cluster, multi-stage few clusters, and large-stage multiple clusters. Each fracturing mode has at least two, which are separated. Different fracturing modes use proppants of different colors. At the same time, the root of the horizontal well for plane fracture length observation is designed separately in one of the three modes: single-segment single cluster, multiple-segment few clusters, and large-segment multiple clusters, and the number of designed segments is at least greater than eight to ensure the accuracy of the fracture length parameters; since the two observation horizontal wells are adjacent, in order to distinguish them, the proppant of the fracture well is not dyed.

5. The method for determining the coring well group for observation of artificial fracture parameters of shale oil platform fracturing according to claim 1, characterized in that: In step 4, the specific process is: For key observation horizontal wells, downhole microseismic or sonar remote fracture monitoring technology is used to obtain the key fracture test parameters of fracture length and fracture height of the key observation horizontal wells; at the same time, by conducting downhole television hole erosion monitoring on the observation horizontal wells, it is ensured that the opening rate of each cluster in the root fracturing design section of the observation horizontal well is >80%, thereby ensuring the hydraulic fracturing transformation effect.

6. The method for determining the coring well group for observation of artificial fracture parameters of shale oil platform fracturing according to claim 1, characterized in that: In step 5, the specific process is: 5.1) Set up a horizontal well group for longitudinal fracture height observation: A total of four longitudinal fracture height monitoring coring wells are designed, including two high-angle coring wells and two horizontal wells; First, two highly deviated coring wells X1 and X2 were implemented. The plane projection of the highly deviated coring well was parallel to the observation horizontal well, and the plane distance from the observation horizontal well was less than 10% of the half-fracture length of the fracture test. The two highly deviated coring wells were symmetrical around the observation horizontal well. Well X1 cored from the top of the reservoir to the bottom, and well X2 cored from the bottom of the reservoir to the top of the formation. The vertical distance of the two wells passing through the reservoir must be greater than the average value of the upper fracture height of the fracture test reservoir; the vertical distance of the two wells passing through the reservoir must be greater than the average value of the lower fracture height of the fracture test reservoir, and the microseismic event points in the coring section were active. Then, based on the observation of artificial fractures in two highly deviated coring wells, two horizontal coring wells P1 and P2 are arranged symmetrically around the observation horizontal well. The distance between the horizontal coring well and the observation horizontal well is 1 / 2 of the distance between the highly deviated coring well and the observation horizontal well. Among them, P1 well is located above the reservoir, and the coring direction is the line connecting the highest points O1→O2 of the artificial fracture coring observations in the two highly deviated coring wells; P2 well is located below the reservoir, and the coring direction is the line connecting the highest points O3→O4 of the artificial fracture coring observations in the two highly deviated coring wells; the vertical distances of the artificial fractures observable in the cores of P1 and P2 wells from the middle of the oil layer are counted, and their average values ​​are taken as the actual upper fracture height and lower fracture height of fracturing; 5.2) Set up a horizontal well group for plane fracture length observation: A total of four horizontal coring wells are arranged in the horizontal well group for plane fracture length observation; First, two horizontal coring wells, B1 and B2, were implemented. The minimum distance between the two horizontal coring wells B1 and B2 and the fracture length observation horizontal well was less than 10% of the half fracture length of the fracture test, and the maximum distance was the average value of the half fracture length. One well was cored from the observation horizontal well from near to far, and the other well was cored from the observation horizontal well from far to near. Then, the maximum points O5 and O6 of the half-fracture length observed by coring of the artificial fractures in the two horizontal coring wells B1 and B2 are obtained, and two more coring wells B3 and B4 are set in the direction of the line O5-O6 and the direction symmetrical around the observed horizontal well; the vertical distances of all the artificial fractures observed in the two coring wells B3 and B4 from the observed horizontal well are counted respectively, and their average values ​​are taken as the left and right half-fracture lengths of the artificial fractures.

7. The method for determining the coring well group for observation of artificial fracture parameters of shale oil platform fracturing according to claim 1, characterized in that: In step 6, the specific process is: According to the half-fracture length and fracture height data obtained in step 5, the horizontal well spacing of the shale oil platform for single-layer development is greater than or equal to the fracture length counted by the coring well group, and the thickness of the vertical interlayer of the three-dimensional development platform is greater than or equal to the fracture height counted by the coring well group. The shale oil platform well network is set up accordingly.

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