While-drilling natural crack calibration and risk prediction method

Abstract

The invention relates to a while-drilling natural crack calibration and risk prediction method. The method comprises the following steps: S1, carrying out data information standardization processing; s2, carrying out correlation analysis on adjacent wells, preferably selecting two wells with high correlation, and establishing a well connection profile; s3, establishing a natural crack correction initial model; s4, correcting the well depth corresponding to the drilled natural fracture by using the actual depth of each drilled stratum of the target well; correcting the well depth corresponding to the natural fracture at the position according to the lithology of the forward drilling formation, the logging while drilling information or the drilling engineering abnormity, and predicting the well depth corresponding to the natural fracture around the well in the later period by combining the previous prediction and actual drilling depth error; and S5, for the predicted well depth corresponding to the natural fracture, qualitatively analyzing the crustal stress borne by the fracture through the geophysical prospecting profile around the well, measuring the size of the included angle of the fracture, and predicting the geological risks such as leakage, collapse and blocking at the position of the target well. According to the method, the accuracy and reliability of the predicted depth can be ensured, a geological basis is provided for smooth construction of the well, and a reference is provided for later-stage well spacing and fracture prediction of the region.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration and development, and more specifically to a method for natural fracture calibration and risk prediction while drilling. Background Art

[0002] In the exploration and development of shale gas, some wells have many leakage layers and large leakage volume, most of which are fracture leakage. After statistics and analysis, the main geological cause of regional well leakage and drill stuck is the development of faults and natural fractures around the wells after multiple periods of complex geological tectonic movements. Based on this, we urgently need a method to accurately determine the depth of faults and fractures around the target wells, design well trajectories to avoid faults and fractures, or take other anti-leakage and anti-stuck measures to reduce the risk of drill stuck and the economic losses caused by drilling fluid leakage.

[0003] In the interpretation and prediction of fault fractures, geophysical technology plays an irreplaceable and important role, especially the fault fracture identification method based on seismic attributes. Coherence body technology is one of the most outstanding fracture identification technologies at present. Coherence body technology reflects the similarity of seismic data in the form of coherent attributes, and can highlight the overall spatial development characteristics of faults, microfractures, lithology or geological structures through coherence changes. It has the following advantages: ① Simplifying the complex, converting complex seismic data into a single coherence value, reflecting the spatial distribution of faults according to the coherence difference, and eliminating redundant information interference; ② There are few parameters involved in the calculation, including only the size of the analysis time window and the search dip, and the calculation speed is fast. However, the difference in coherence does not necessarily strictly correspond to the fault. Some changes in lithology or special geological bodies such as anticlines can cause changes in coherence.

[0004] Curvature attribute is a very popular fault identification method in recent years, which has both high noise resistance and good three-dimensional visualization interpretation function. From the curvature distribution of the fault structure, it can be seen that the smoothed horizon interpretation line has a curvature change from positive to negative or from negative to positive, so the fault, fracture and other structures can be effectively identified through the curvature change of the geological body itself. However, compared with the volume curvature directly extracted from the seismic data body, the surface curvature still has great limitations: ① The surface curvature is extracted from the interpolated horizon interpretation result, which is easily affected by factors such as manual interpretation and software interpolation, resulting in local non-closure phenomenon, reducing the accuracy of fault identification; ② Seismic data is not involved in the calculation, so the fault response on the surface curvature does not necessarily correspond to the real fault structure.

[0005] In summary, the use of seismic attribute coherence, curvature, ant body, maximum likelihood or wave impedance to predict faults in micro-amplitude structures around the target well has certain limitations and errors. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for calibrating and predicting risks of natural fractures while drilling, introduce the formation lithology, logging data while drilling, or drilling engineering anomalies during the drilling process to compare and calculate the predicted depth of fractures in the drilled formation with the actual depth, and use the calculated results as correction values ​​to participate in the calculation of the predicted depth of natural fractures in the drilling formation or the formation to be drilled, thereby reducing the depth deviation of the fracture prediction before drilling. During the drilling process, according to the correction results, real-time preparations for leak prevention and anti-sticking are made to ensure smooth drilling construction.

[0007] The technical solution adopted by the present invention to solve the technical problem is: combining regional geophysical exploration, geological and drilling data to carry out standardized processing of target well and adjacent well data, and conducting adjacent well correlation analysis to establish a well-connected profile, using seismic inversion attributes to establish an initial model for accurate fracture depth correction of the target well, and combining formation lithology, logging data while drilling, or drilling engineering anomalies during the drilling process to correct the predicted depth of formation fractures again, so as to improve the accuracy of the predicted depth, including the following steps:

[0008] S1. Data standardization is carried out based on the well foundation, actual drilling well inclination, stratigraphic division, gas logging and lithology data of the regional neighboring wells and the well foundation, design trajectory and actual drilling trajectory data of the target wells;

[0009] S2. Conduct correlation analysis of adjacent wells, select two wells with high correlation, and establish a well-connected profile;

[0010] S3. Based on the well-connected profile, the target well along the well trajectory profile is cut in combination with one of the seismic inversion attributes of coherence, curvature, ant body, maximum likelihood or wave impedance to establish an initial model for natural fracture correction;

[0011] S4. During the drilling process of the target well, the segmented multi-point while-drilling profile correction method is used to drill and correct each layer of the target well and predict the next layer. The actual depth of each formation drilled by the target well is used to correct the corresponding well depth of the drilled natural fractures. The corresponding well depth of the natural fractures in the current layer is corrected according to the lithology of the formation being drilled, the while-drilling logging data, or the drilling engineering anomalies. In addition, the corresponding well depth of the natural fractures around the well in the later stage is predicted based on the error between the previous prediction and the actual drilling depth.

[0012] S5. For the predicted natural fractures corresponding to the well depth, the geostress state of the fractures is qualitatively analyzed through the geophysical profile around the well, and the angle of the fractures is measured to predict the geological risks such as leakage and collapse of the target well.

[0013] According to the above scheme, in step S1, the well basis of regional neighboring wells, actual drilling well deviation, stratigraphic division, gas logging and lithology data, and the well basis of target wells, designed trajectory, and actual drilling trajectory data are subjected to data standardization processing, specifically including the following steps:

[0014] S101. Based on the data import requirements of the guidance software used, the well foundation, actual drilling inclination, designed trajectory, stratigraphic division, gas measurement and lithology data of the target well and adjacent wells are produced or converted into corresponding formats as required.

[0015] S102. Create a new work area in the study area and import the prepared target well and adjacent well data into the work area to provide a basis for subsequent depth correction comparison and precision analysis.

[0016] According to the above scheme, in step S2, the correlation analysis of adjacent wells is carried out, two wells with high correlation are selected, and a well-connected profile is established. The specific contents are as follows:

[0017] S201. Different weights are assigned to factors such as formation continuity, belonging to the same local structural unit without fault separation or distance, and correlation analysis between the target well and adjacent wells is carried out to select two wells with high correlation.

[0018] S202, based on the actual depth data of the formations drilled in the adjacent wells, and the relative positions of the wellhead coordinates of the target well and the two adjacent wells, a formation well-connected profile is established to facilitate the subsequent layer-by-layer fault correction.

[0019] According to the above scheme, in step S3, based on the well-connected profile, the target well along the well trajectory profile is cut in combination with one of the seismic inversion attributes of coherence, curvature, ant body, maximum likelihood or wave impedance, and an initial model for natural fracture correction is established, which specifically includes the following steps:

[0020] S301, according to the previous coherent attribute volume model, cut out the coherent attribute section along the well section direction in step S2;

[0021] S302, according to the previous curvature attribute body model, cutting out the curvature attribute section along the well section direction in step S2;

[0022] S303, according to the previous ant body attribute body model, cut out the ant body attribute section along the well along the direction of the well section in step S2;

[0023] S304, according to the previous maximum likelihood attribute volume model, cutting out the maximum likelihood attribute section along the well along the direction of the well section in step S2;

[0024] S305, according to the previous wave impedance attribute body model, cut out the wave impedance inversion section along the well section direction in step S2;

[0025] S306, analyzing and comparing the five attribute maps obtained in the above five sub-steps, selecting the most suitable one according to regional experience and the commonalities in the attribute maps, combining the well-connected profile in S2, using the two corresponding points in the two maps, superimposing the two maps to establish an initial model for natural fracture correction.

[0026] According to the above scheme, in step S4, during the drilling process of the target well, the segmented multi-point while-drilling profile correction method is used to drill and correct one layer of the target well, and predict the next layer. The actual depth of each formation drilled by the target well is used to correct the corresponding well depth of the drilled natural fractures; the corresponding well depth of the natural fractures in the current layer is corrected according to the lithology of the formation being drilled, the while-drilling logging data, or the drilling engineering anomaly, and the previous prediction and the actual drilling depth error are combined to predict the corresponding well depth of the natural fractures around the well in the later stage, which specifically includes the following steps:

[0027] S401, obtaining the accurate depth of natural fractures in the actual drilling formation according to the logging, well logging and logging while drilling data of the current actual drilling formation, and translating the section corresponding to each predicted fracture in the upper formation up and down on the initial model for natural fracture correction to make it correspond to the fracture depth of the actual formation, completing the correction of the natural fracture corresponding to the well depth in the drilled formation, and recording the data difference between the predicted depth and the actual depth;

[0028] S402. In the drilling formation, according to whether there are drilling engineering geological anomalies such as blowdown, lost circulation in the fracture zone, stuck pipe in the fracture zone, increased rock block drop in the fracture zone, abnormal increase in gas logging base value, or the real depth of the fracture in the drilling formation is determined according to the logging while drilling data, the natural fractures predicted before within the range of ±λ / 4 (λ is the wavelength of the seismic wave) are translated to this depth, and the data difference between the predicted depth of the fracture and the actual depth is recorded;

[0029] S403. In the formation to be drilled, according to the data differences between all predicted depths and actual depths recorded in S401 and S402, find the variation law of the differences, and on the basis of this variation law, correct the well depth corresponding to the natural fractures predicted before the formation to be drilled, and complete the final correction of the well depth corresponding to the natural fractures.

[0030] According to the above scheme, in step S5, for the predicted well depth corresponding to the natural fracture, the ground stress state of the fracture is qualitatively analyzed through the geophysical profile around the well, and the fracture angle is measured to predict the geological risks such as leakage and jamming at the target well, which specifically includes the following steps:

[0031] S501. Determine whether the fracture is subjected to compression or tension based on the local micro-radial structure and fracture properties of the formation in the geophysical profile around the well, and determine whether the fracture is a high-angle fracture or a low-angle fracture based on the angle between the fracture and the horizontal direction;

[0032] S502. The pulling and squeezing states and high and low angle seams can be freely combined into four forms. According to experience, the high angle seams under pulling have a high risk of collapse, the high angle seams under pulling have a high risk of leakage, the low angle seams under squeezing have a low geological risk, and the high angle seams under squeezing have a high risk of drill sticking.

[0033] According to the above scheme, in step S1, data standardization processing is carried out based on the well foundation of regional neighboring wells, actual drilling well inclination, stratigraphic division, gas logging and lithology data, as well as the well foundation, designed trajectory, and actual drilling trajectory data of the target well, so as to provide a reference standard for subsequent result comparison and detailed analysis.

[0034] According to the above scheme, in step S2, a correlation analysis is conducted on the micro-geological structure around the main target layer of the target well in the study area, and a well-connected profile is established for the same layer as the target well in the adjacent wells to facilitate subsequent stratigraphic comparison.

[0035] According to the above scheme, in step S3, the method of predicting natural fractures using previous geophysical data in the study area is combined with one of the seismic inversion attributes of coherence, curvature, ant body, maximum likelihood or wave impedance to cut the target well along the well trajectory profile and establish an initial model for natural fracture correction.

[0036] According to the above scheme, in step S4, the formation lithology, logging data while drilling, or drilling engineering anomalies during the drilling process are introduced to compare and calculate the predicted depth of the drilled formation fractures with the actual depth, and the calculation result is used as a correction value to participate in the calculation of the predicted depth of natural fractures in the drilling formation or the formation to be drilled, and the accuracy of the calculation result is analyzed.

[0037] According to the above scheme, in step S4, the prediction error of the well depth corresponding to the natural fractures in the formation being drilled is less than 2%, and the prediction error of the well depth corresponding to the natural fractures in the formation to be drilled is less than 2%, and the model has high accuracy.

[0038] According to the above scheme, in step S5, the geological risk at the crack is comprehensively judged by using the ground stress state of the crack and the crack angle.

[0039] The present invention also provides a common guidance software, including a data management module, a three-dimensional seismic volume data or a two-dimensional seismic profile loading module, and a guidance analysis and display module. The data management module and the seismic data loading module are mainly used to import the basic geological data required for the above analysis, and the main operation is performed step by step according to the instructions or steps in the guidance analysis and display module. The guidance analysis module can perform any and all of the above methods step by step.

[0040] The implementation of the method for natural fracture calibration and risk prediction while drilling of the present invention has the following beneficial effects:

[0041] 1. The present invention makes full use of drilling engineering anomalies, logging data and logging data while drilling in the study area to determine the true depth of fractures in the drilling formation. Through the data difference between the predicted depth and the actual depth of fractures in all drilled formations, the variation law of the difference is found. Based on this variation law, the natural fracture depth predicted before the formation to be drilled is corrected, and the prediction model of the corresponding well depth of natural fractures in the target well is improved, thereby realizing the correction of the natural fracture depth.

[0042] 2. The present invention introduces the formation lithology, logging data while drilling, or drilling engineering anomalies during the drilling process to compare and calculate the predicted depth of the drilled formation fracture with the actual depth, and uses the calculated result as a correction value to participate in the calculation of the predicted depth of natural fractures in the drilling formation or the formation to be drilled, thereby reducing the depth deviation of the fracture prediction before drilling. During the drilling process, according to the correction result, real-time preparations for leak prevention and anti-sticking are made to ensure smooth drilling construction.

[0043] 3. The present invention is simple to operate and easy to promote and apply. It can effectively reduce the precision error of the fracture depth prediction for the seismic attribute body, ensure the accuracy and reliability of the predicted depth, provide a geological basis for the smooth construction of the well, and provide a reference for the later well layout and fracture prediction in the region. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0045] Figure 1 This is a flow chart of a method for natural fracture calibration and risk prediction while drilling according to the present invention;

[0046] Figure 2 It is the data management module diagram of the geological data of the target well and the adjacent wells;

[0047] Figure 3 It is a cross-sectional view of the wells connected through the target well and the adjacent wells;

[0048] Figure 4 is the coherent attribute plane diagram of the target well and the adjacent wells;

[0049] Figure 5 The curvature attribute profile along the well cut in the direction of the well section;

[0050] Figure 6 It is the cross-section diagram of the ant body properties along the well cut in the direction of the well section;

[0051] Figure 7 The maximum likelihood attribute profile along the well cut out in the direction of the well section;

[0052] Figure 8 The wave impedance attribute profile along the well cut in the well section direction;

[0053] Fig. 9 It is a multi-point correction diagram of the natural fractures in the drilled formation corresponding to the well depth;

[0054] Fig.10 This is the model diagram for the correction of the well depth corresponding to the natural fractures in the formation to be drilled. DETAILED DESCRIPTION

[0055] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention are now described in detail with reference to the accompanying drawings. The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the present invention to the disclosed forms. Many modifications and variations are obvious to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention, and to enable those of ordinary skill in the art to understand the present invention and design various embodiments with various modifications suitable for specific purposes.

[0056] The method for calibrating and predicting the risk of natural fractures while drilling of the present invention introduces the formation lithology, logging data while drilling, or drilling engineering anomalies in the drilling process to compare and calculate the predicted depth of the fractures in the drilled formation with the actual depth, and uses the calculated result as a correction value to participate in the calculation of the predicted depth of natural fractures in the formation being drilled or the formation to be drilled, thereby reducing the depth deviation of the fracture prediction before drilling. During the drilling process, according to the correction result, the preparation work for leak prevention and anti-sticking is done in real time to ensure the smooth progress of the drilling construction.

[0057] The present invention combines regional geophysical exploration, geology and drilling data to carry out standardized processing of target well and adjacent well data, and conducts adjacent well correlation analysis to establish a well-connected profile, uses seismic inversion attributes to establish an initial model for accurate fracture depth correction of the target well, and combines formation lithology, logging data while drilling, or drilling engineering anomalies during the drilling process to correct the predicted depth of formation fractures again, thereby improving the accuracy of the predicted depth, and includes the following steps:

[0058] S1. Data standardization is carried out based on the well foundation, actual drilling well inclination, stratigraphic division, gas logging and lithology data of the regional neighboring wells and the well foundation, design trajectory and actual drilling trajectory data of the target wells;

[0059] S2. Conduct correlation analysis of adjacent wells, select two wells with high correlation, and establish a well-connected profile;

[0060] S3. Based on the well-connected profile, the target well along the well trajectory profile is cut in combination with one of the seismic inversion attributes of coherence, curvature, ant body, maximum likelihood or wave impedance to establish an initial model for natural fracture correction;

[0061] S4. During the drilling process of the target well, the segmented multi-point while-drilling profile correction method is used to drill and correct one layer of the target well, and predict the next layer. The actual depth of each formation drilled by the target well is used to correct the corresponding well depth of the drilled natural fractures; the corresponding well depth of the natural fractures in this layer is corrected according to the lithology of the formation being drilled, the logging data while drilling, or the abnormalities of the drilling project, and the corresponding well depth of the natural fractures around the well is predicted in the future according to the error between the previous prediction and the actual drilling depth.

[0062] S5. For the predicted natural fractures corresponding to the well depth, the geostress state of the fractures is qualitatively analyzed through the geophysical profile around the well, and the angle of the fractures is measured to predict the geological risks such as leakage and collapse of the target well.

[0063] Preferably, in step S1, the well basis of regional neighboring wells, actual drilling well deviation, stratigraphic division, gas logging and lithology data, and the well basis of target wells, designed trajectory, and actual drilling trajectory data are subjected to data standardization processing, specifically including the following steps:

[0064] S101. Based on the data import requirements of the guidance software used, the well foundation, actual drilling inclination, designed trajectory, stratigraphic division, gas measurement and lithology data of the target well and adjacent wells are produced or converted into corresponding formats as required.

[0065] S102. Create a new work area in the study area and import the prepared target well and adjacent well data into the work area to provide a basis for subsequent depth correction comparison and precision analysis.

[0066] Preferably, in step S2, a correlation analysis of adjacent wells is carried out, two wells with high correlation are selected, and a well-connected profile is established, and the specific contents are as follows:

[0067] S201. Different weights are assigned to factors such as formation continuity, belonging to the same local structural unit without fault separation or distance, and correlation analysis between the target well and adjacent wells is carried out to select two wells with high correlation.

[0068] S202, based on the actual depth data of the formations drilled in the adjacent wells, and the relative positions of the wellhead coordinates of the target well and the two adjacent wells, a formation well-connected profile is established to facilitate the subsequent layer-by-layer fault correction.

[0069] Preferably, in step S3, based on the well-connected profile, the target well along the well trajectory profile is cut in combination with one of the seismic inversion attributes of coherence, curvature, ant body, maximum likelihood or wave impedance to establish an initial model for natural fracture correction, which specifically includes the following steps:

[0070] S301, according to the previous coherent attribute volume model, cut out the coherent attribute section along the well section direction in step S2;

[0071] S302, according to the previous curvature attribute body model, cutting out the curvature attribute section along the well section direction in step S2;

[0072] S303, according to the previous ant body attribute body model, cut out the ant body attribute section along the well along the direction of the well section in step S2;

[0073] S304, according to the previous maximum likelihood attribute volume model, cutting out the maximum likelihood attribute section along the well along the direction of the well-connected section in step S2;

[0074] S305, according to the previous wave impedance attribute body model, cut out the wave impedance inversion section along the well section direction in step S2;

[0075] S306, analyzing and comparing the five attribute maps obtained in the above five sub-steps, selecting the most suitable one according to regional experience and the commonalities in the attribute maps, combining the well-connected profile in S2, using the two corresponding points in the two maps, superimposing the two maps to establish an initial model for natural fracture correction.

[0076] Preferably, in step S4, during the drilling of the target well, a segmented multi-point while-drilling profile correction method is used to drill and correct one layer of the target well, and predict the next layer. The actual depth of each formation drilled in the target well is used to correct the corresponding well depth of the drilled natural fractures; the corresponding well depth of the natural fractures in the current layer is corrected according to the lithology of the formation being drilled, the while-drilling logging data, or the drilling engineering anomaly, and the previous prediction and the actual drilling depth error are combined to predict the corresponding well depth of the natural fractures around the well in the later stage, which specifically includes the following steps:

[0077] S401, obtaining the accurate depth of natural fractures in the actual drilling formation according to the logging, well logging and logging while drilling data of the current actual drilling formation, and translating the section corresponding to each predicted fracture in the upper formation up and down on the initial model for natural fracture correction to make it correspond to the fracture depth of the actual formation, completing the correction of the natural fracture corresponding to the well depth in the drilled formation, and recording the data difference between the predicted depth and the actual depth;

[0078] S402. In the drilling formation, according to whether there are drilling engineering geological anomalies such as blowdown, lost circulation in the fracture zone, stuck pipe in the fracture zone, increased rock block drop in the fracture zone, abnormal increase in gas logging base value, or the real depth of the fracture in the drilling formation is determined according to the logging while drilling data, the natural fractures predicted before within the range of ±λ / 4 (λ is the wavelength of the seismic wave) are translated to this depth, and the data difference between the predicted depth of the fracture and the actual depth is recorded;

[0079] S403. In the formation to be drilled, according to the data differences between all predicted depths and actual depths recorded in S401 and S402, find the variation law of the differences, and on the basis of this variation law, correct the well depth corresponding to the natural fractures predicted before the formation to be drilled, and complete the final correction of the well depth corresponding to the natural fractures.

[0080] Preferably, in step S5, for the predicted well depth corresponding to the natural fracture, the geostress state of the fracture is qualitatively analyzed through the geophysical profile around the well, and the fracture angle is measured to predict the geological risks such as leakage and jamming at the target well, which specifically includes the following steps:

[0081] S501. Determine whether the fracture is subjected to compression or tension based on the local micro-radial structure and fracture properties of the formation in the geophysical profile around the well, and determine whether the fracture is a high-angle fracture or a low-angle fracture based on the angle between the fracture and the horizontal direction;

[0082] S502. The pulling and squeezing states and high and low angle seams can be freely combined into four forms. According to experience, the high angle seams under pulling have a high risk of collapse, the high angle seams under pulling have a high risk of leakage, the low angle seams under squeezing have a low geological risk, and the high angle seams under squeezing have a high risk of drill sticking.

[0083] Example

[0084] See also Figures 1 to 10 In this embodiment, a method for natural fracture calibration and risk prediction while drilling is provided, comprising the following steps:

[0085] S1. Data standardization is carried out based on the well foundation, actual drilling well inclination, stratigraphic division, gas logging and lithology data of the neighboring wells in the region, as well as the well foundation, designed trajectory and actual drilling trajectory data of the target well: Data standardization is carried out using Well A as an example. The standardization processing is shown in Tables 1 to 5.

[0086] Table 1 Well basic standardized information

[0087]

[0088] Table 2 Standardized information of designed trajectory / actual drilling trajectory

[0089]

[0090] Table 3 Standardized information of stratigraphic division

[0091]

[0092] Table 4 Gas measurement data standardization information

[0093]

[0094] Table 5 Standardized information of lithology data

[0095]

[0096] S2. Conduct correlation analysis of adjacent wells, select two wells with high correlation, and establish a well-connected profile. By assigning different weights to multiple factors: formation continuity 0.3, local structural unit difference 0.4, and well distance 0.3, select two adjacent wells with high correlation.

[0097] Table 6 Correlation analysis of adjacent wells

[0098] well name Stratigraphic continuity Structural differences Distance Total score Neighboring Well A 1 1 1 1 Neighboring well B 1 1 1 1 Neighboring Well C 1 1 0 0.7 Neighboring well D 1 0 0 0.3 Neighboring Well E 0 0 1 0.3

[0099] S3. Use the two adjacent wells selected in S2 as references to establish a well-connected profile. Combine the coherence, curvature, ant body, maximum likelihood or commonality of wave impedance, select one of the wave impedance seismic inversion attributes to cut the target well along the well trajectory, and establish an initial model for natural fracture correction.

[0100] S4. Using the natural fracture correction initial model established in S3, during the drilling process of the target well, the segmented multi-point while-drilling profile correction method is used to drill and correct one layer of the target well and predict the next layer. 0 The actual depth of 6880m and the leakage depth of F1 fault zone of 6792m were used to correct the depth of the intersection center of the drilled natural fracture F1 and the well trajectory to 6792m; according to the emptying and leakage point of the drilling formation at 7410m, the top depth of the natural fracture F2 in this layer was corrected to 7410m, and the predicted F2 fault zone (oblique depth of 7445-7460m) was shifted upward by 35m to make it consistent with the actual situation; finally, combined with the previous prediction and the actual drilling depth error of 35m, the predicted depth of the natural fracture F3 around the well in the later period was changed from the oblique depth of 7690-7700m to the predicted oblique depth of F3 of 7655-7665m.

[0101] S5. Based on the corresponding well depths of the F2 and F3 fault zones predicted in S4, the pulling and squeezing states of F2 and F3 were analyzed, and it was determined that F2 was a high-angle fracture and F3 was a low-angle fracture. It was predicted that the leakage risk at the F2 fault zone (oblique depth 7410-7425m) was extremely high, and the leakage risk at F3 (oblique depth 7655-7665m) was small.

[0102] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for natural fracture calibration and risk prediction while drilling, characterized in that: The following steps are involved: S1. Data standardization is carried out based on the well foundation, actual drilling well inclination, stratigraphic division, gas logging and lithology data of the regional neighboring wells and the well foundation, design trajectory and actual drilling trajectory data of the target wells; S2. Conduct correlation analysis of adjacent wells, select two wells with high correlation in micro-geological structures around the wells, and establish a well-connected profile; S3, based on the well-connected profile established in S2, a profile of the target well along the well trajectory is cut in combination with one of the seismic inversion attributes of coherence, curvature, ant body, maximum likelihood or wave impedance, and an initial model for natural fracture correction is established; S4. Using the natural fracture correction initial model established in S3, during the drilling process of the target well, the segmented multi-point while-drilling profile correction method is used to drill and correct one layer of the target well and predict the next layer; using the actual depth of each formation drilled by the target well, the corresponding well depth of the drilled natural fracture is corrected; according to the lithology of the formation being drilled, the while-drilling logging data, or the drilling engineering anomaly, the natural fracture depth of the current layer is corrected, and combined with the previous prediction and the actual drilling depth error, the seismic profile of the lower formation is translated up and down to predict the corresponding well depth of the natural fractures around the well in the later period; S5. For the predicted natural fractures at the corresponding well depth, the geostress state of the fractures is qualitatively analyzed through the geophysical profile around the well, and the fracture angle is measured to predict the geological risk of the target well.

2. The method for natural fracture calibration and risk prediction while drilling according to claim 1, characterized in that: The step S1 specifically includes the following steps: S101. Based on the data import requirements of the used guidance software, the well foundation, actual drilling inclination, designed trajectory, formation division, gas measurement and lithology data of the target well and adjacent wells are prepared or converted into corresponding formats as required; S102. Create a new work area in the study area and import the data of the target well and adjacent wells into the work area.

3. The method for natural fracture calibration and risk prediction while drilling according to claim 1, characterized in that: The step S2 specifically includes the following steps: S201. Different weights are assigned to factors such as formation continuity, belonging to the same local structural unit without fracture separation or distance, etc., and correlation analysis between the target well and the adjacent wells is carried out to select two wells with high correlation; S202: Establish a formation well-connected profile based on the actual depth data of the drilled formations of the adjacent wells and the relative positions of the wellhead coordinates of the target well and the two adjacent wells.

4. The method for natural fracture calibration and risk prediction while drilling according to claim 1, characterized in that: The step S3 specifically comprises the following steps: S301, according to the previous coherent attribute volume model, cut out the coherent attribute section along the well section direction in step S2; S302, according to the previous curvature attribute body model, cutting out the curvature attribute section along the well section direction in step S2; S303, according to the previous ant body attribute body model, cut out the ant body attribute section along the well along the direction of the well section in step S2; S304, according to the previous maximum likelihood attribute volume model, cutting out the maximum likelihood attribute section along the well along the direction of the well section in step S2; S305, according to the previous wave impedance attribute body model, cut out the wave impedance inversion section along the well section direction in step S2; S306, analyzing and comparing the five attribute maps obtained in the above five sub-steps, selecting the most suitable one, combining it with the well-connected profile in S2, using two corresponding points in the two maps, superimposing the two maps to establish an initial model for natural fracture correction.

5. The method for natural fracture calibration and risk prediction while drilling according to claim 1, characterized in that: The step S4 specifically comprises the following steps: S401, obtaining the accurate depth of natural fractures in the actual drilling formation according to the logging, well logging and logging while drilling data of the currently drilled formation, and translating up and down the section corresponding to each predicted fracture in the upper formation on the initial model for natural fracture correction so that it corresponds to the fracture depth of the actual formation, completing the correction of the natural fracture depth of the drilled formation, and recording the data difference between the predicted depth and the actual depth; S402, in the drilling formation, according to whether there is a drilling engineering geological anomaly, or according to the logging data while drilling, the real depth of the fracture in the drilling formation is determined, and the natural fracture previously predicted within the range of ±λ / 4 of this depth value is translated to this depth, where λ is the wavelength of the seismic wave, and the data difference between the previously predicted depth of this fracture and the actual depth is recorded; S403. In the formation to be drilled, according to the data differences between all predicted depths and actual depths recorded in S401 and S402, find the variation law of the differences, and on the basis of this variation law, correct the natural fracture depth predicted before the formation to be drilled, so as to complete the natural fracture depth correction.

6. The method for natural fracture calibration and risk prediction while drilling according to claim 1, characterized in that: The step S5 specifically comprises the following steps: S501. Determine whether the fracture is subjected to compression or tension based on the local micro-radial structure and fracture properties of the formation in the geophysical profile around the well, and determine whether the fracture is a high-angle fracture or a low-angle fracture based on the angle between the fracture and the horizontal direction; S502. The pulling and squeezing states and high and low angle seams are freely combined into four forms. Based on experience, it is judged that the high angle seams under pulling have a high risk of collapse, the high angle seams under pulling have a high risk of leakage, the low angle seams under squeezing have a low geological risk, and the high angle seams under squeezing have a high risk of drill sticking.

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