Dynamic wellbore structure optimization design method during drilling based on while-drilling data

Abstract

The present invention discloses a method for optimizing the dynamic wellbore structure during drilling based on the data while drilling. First, the pore pressure of the formation with credibility is predicted before drilling based on the seismic layer velocity; then the pore pressure of the formation with credibility is corrected in real time based on the logging data while drilling; and finally, the dynamic wellbore structure risk is evaluated during drilling. The pore pressure of the formation with credibility is corrected in real time by the logging data while drilling, so as to improve the pressure prediction accuracy of the lower undrilled formation, and a dynamic wellbore structure risk evaluation method during drilling is established in combination with the safety density window constraint condition and probability theory, so as to perform a real-time quantitative evaluation of the wellbore structure risk of the lower undrilled formation during drilling. And according to the final evaluation, it is determined whether to redesign the wellbore structure of the lower undrilled formation in real time, so as to avoid engineering risks to the greatest extent.

Description

Technical Field

[0001] The invention relates to the field of deep well complex formation drilling, and in particular to a dynamic wellbore structure optimization design method during the drilling process based on while-drilling data. Background Art

[0002] The narrow safety density window problem in deep well drilling in complex formations has always been one of the difficulties faced by wellbore structure design and safe construction, and as the well depth increases, the narrow safety density window problem becomes more and more prominent. Existing technologies generally use advanced new process technologies such as underbalanced drilling, managed pressure drilling, and aerated drilling, as well as risk assessment technologies such as pre-drilling wellbore structure design and risk assessment methods based on probability statistics, which have solved this problem to a certain extent.

[0003] However, new technologies such as underbalanced drilling, managed pressure drilling, and aerated drilling in the existing technologies, as well as risk assessment technologies such as pre-drilling wellbore structure design and risk assessment methods based on probability statistics, do not combine the accurate determination of pre-drilling uncertainty parameters such as formation pressure and rock mechanics parameters of the drilled section, and therefore cannot eliminate the potential risks caused by formation uncertainty parameters from the root. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides a dynamic wellbore structure optimization design method during the drilling process based on downhole data, so as to solve the problem that new process technologies such as underbalanced drilling, pressure-controlled drilling, and aerated drilling in the prior art, as well as risk assessment technologies such as pre-drilling wellbore structure design and risk assessment methods based on probability statistics are not combined with accurate determination of pre-drilling uncertainty parameters such as formation pressure and rock mechanics parameters of the drilled section, resulting in potential risks.

[0005] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0006] The dynamic wellbore structure optimization design method during drilling based on the drilling data includes:

[0007] Step 1: Pre-drilling reliable formation pore pressure prediction based on seismic interval velocity;

[0008] Step 2: Correct the pore pressure of the reliable formation in real time based on the logging while drilling data;

[0009] Step 3: Dynamic wellbore structure risk assessment during drilling.

[0010] Preferably, the prediction of formation pore pressure with credibility before drilling based on seismic layer velocity in step 1 includes:

[0011] Based on the acquired seismic layer velocity data, preprocessing the seismic layer velocity data to determine the overlying rock pressure gradient;

[0012] Calculate formation pore pressure based on Fillippone method;

[0013] Inversely calculate the Eaton index in combination with the Eaton method, and obtain the distribution state based on the Eaton index;

[0014] Re-substitute the Eaton method to calculate the reliable formation pore pressure.

[0015] Preferably, the real-time correction of the reliable formation pore pressure based on the logging while drilling data in step 2 includes:

[0016] (1) Calculation of formation pore pressure G based on seismic data p , Combined with the Eaton method to calculate the Eaton index, a large sample library n(h) is obtained, and the Eaton index of the entire well section is counted to obtain the distribution status;

[0017] (2) Based on the formation pore pressure G obtained by logging while drilling p ′, invert the Eaton index of the drilled section and obtain the small sample library n′(h 1 ), and n′(h 1 ) replaces the Eaton index n(h) of the drilled section 1 ) to form a new large sample library n′(h) and obtain a new distribution state; and then re-substitute the Eaton method to calculate the credible pore pressure of the lower undrilled formation.

[0018] Preferably, after obtaining the formation credible pore pressure, step 2 further includes:

[0019] Using the formula Calculate the formation fracture pressure P corresponding to the formation pore pressure at different probabilities under the condition of confidence J f ′, where σ h , σ H , α, μ, f and S t To predict the rock mechanical parameters of the next geological layer using the data from adjacent wells;

[0020] When drilling to the preset distance Δh from the top of the next geological layer, the rock mechanical parameters x′(σ h ′、σ H ′, α′, μ′, f′, S t The average value of is the true value of the stratum, and uses Recalculate the formation fracture pressure P of the current geological layer f ″.

[0021] Preferably, the step 2 is performed in the utilization Recalculate the formation fracture pressure P of the current geological layer f "After that, it also includes:

[0022] The average value of each rock mechanical parameter in the well section Δh+δh of the geological layer measured by logging while drilling is The δh is the distance to be drilled when the drilling reaches the preset distance Δh from the top of the next geological layer;

[0023] when When In The average values ​​of the rock mechanical parameters in are replaced by And recalculate the formation fracture pressure p″′ of the geological layer f ,in, It is the average value of various rock mechanical parameters of the local geological layer measured by logging while drilling.

[0024] Preferably, in step 3, the dynamic wellbore structure risk assessment during drilling includes:

[0025] Determine the distribution zone based on the corrected credible formation pressure of the undrilled formation;

[0026] Based on the distribution zone, determining a lower limit curve and an upper limit curve of a safe drilling fluid density window;

[0027] Risk assessment of dynamic wellbore structure during drilling.

[0028] Preferably, the determining distribution zone of the formation pore pressure with credibility based on the corrected undrilled formation comprises:

[0029] Based on the corrected credible formation pressure of the undrilled formation, a calculated value of the formation pressure is determined, wherein the calculated value of the formation pressure includes a credible distribution zone.

[0030] Preferably, the risk assessment of the dynamic wellbore structure during drilling includes:

[0031] Based on the pre-established wellbore structure risk assessment model for the lower undrilled formation, the dynamic wellbore structure risk assessment during the drilling process is performed;

[0032] The risk assessment model of the wellbore structure of the lower undrilled formation includes: well kick risk: Risks of drill bit sticking due to differential pressure: Risk of leakage during drilling: R 井涌(h) , R 压差卡钻(h) , R 钻进井漏(h)are the risk of well kick, differential pressure sticking, and drilling leakage at well depth h; p(x) is the probability of event x; ρ 下 (h) and ρ 上 (h) are the equivalent densities corresponding to the lower limit curve and upper limit curve of the reliable safety drilling fluid density window at the well depth h; is the cumulative probability distribution of formation pore pressure at well depth h; is the cumulative probability distribution of formation fracture pressure at well depth h.

[0033] Preferably, after executing step 3, the dynamic wellbore structure risk assessment during drilling, the method further includes:

[0034] Step 4: If there is a risk in the wellbore during the drilling process, redesign the wellbore structure;

[0035] If there is no risk in the wellbore during the drilling process, execute step 2.

[0036] Preferably, in step 4, if there is a risk in the wellbore during the drilling process, redesigning the wellbore structure includes:

[0037] If there is a risk in the wellbore during the drilling process, a safe drilling fluid density window constraint condition is established; the safe drilling fluid density window constraint condition includes: Among them, ρ pmax ′ is the maximum formation pore pressure gradient in the lower undrilled formation pressure prediction section after correction based on the measurement while drilling data, ρ pmin ′ is the minimum formation pore pressure gradient in the lower undrilled formation pressure prediction section after correction based on the measurement while drilling data, ρ fmin ′ is the minimum formation fracture pressure gradient in the lower undrilled formation pressure prediction section after correction based on the measurement while drilling data, S b ′ is the suction pressure coefficient calculated based on the real-time wellbore structure and drilling conditions, S g ′ is the excitation pressure coefficient calculated based on the real-time wellbore structure and drilling conditions, and Δρ′ is the additional drilling fluid density calculated based on the real-time wellbore structure and drilling conditions.

[0038] From the above content, it can be known that the present invention discloses a method for optimizing the design of dynamic wellbore structure during drilling based on the data while drilling. First, the pore pressure of the formation with credibility is predicted before drilling based on the seismic layer velocity; then the pore pressure of the formation with credibility is corrected in real time based on the logging data while drilling; finally, the dynamic wellbore structure risk is evaluated during drilling. The pore pressure of the formation with credibility is corrected in real time by the logging data while drilling, so as to improve the pressure prediction accuracy of the lower undrilled formation, and a dynamic wellbore structure risk evaluation method during drilling is established in combination with the safety density window constraint condition and probability theory, so as to perform real-time quantitative evaluation of the wellbore structure risk of the lower undrilled formation during drilling. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0040] Figure 1 A flow chart of a method for optimizing the dynamic wellbore structure during drilling based on while-drilling data provided by an embodiment of the present invention;

[0041] Figure 2 A flow chart of formation pore pressure prediction with credibility based on seismic layer velocity provided by an embodiment of the present invention;

[0042] Figure 3 The Eaton index distribution form of the whole well section provided by the embodiment of the present invention;

[0043] Figure 4 A flow chart of formation pore pressure prediction with credibility based on logging while drilling data provided by an embodiment of the present invention;

[0044] Figure 5 A flow chart of dynamic wellbore structure risk assessment during drilling provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] In this application, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0047] The embodiment of the present invention provides a method for optimizing the dynamic wellbore structure during drilling based on the drilling data. Figure 1 and Figure 2 , Figure 1 The present invention is a flow chart of a method for optimizing the dynamic wellbore structure during drilling based on the drilling data. The method comprises at least the following steps:

[0048] Step 1: Pre-drilling reliable formation pore pressure prediction based on seismic interval velocity;

[0049] It should be noted that by predicting the target well pressure based on the seismic layer velocity ratio and using the logging data of adjacent wells, the present application will not be affected by the abundance of adjacent well data, and is also conducive to correcting the pressure of the drilled formation and related calculation parameters in combination with the MWD, LWD and other logging while drilling data.

[0050] In the process of executing step 1, the specific execution process mainly includes the following steps:

[0051] Firstly, based on the acquired seismic layer velocity data, the seismic layer velocity data is preprocessed to determine the overlying rock pressure gradient;

[0052] Secondly, the formation pore pressure is calculated based on the Fillippone method;

[0053] Then, the Eaton index is back-calculated in combination with the Eaton method, and the distribution state is obtained based on the Eaton index;

[0054] Finally, the Eaton method is substituted back to calculate the reliable formation pore pressure.

[0055] It should also be noted that the calculation of formation breakdown pressure requires the use of formation pore pressure. Therefore, the calculated value of formation breakdown pressure also contains a distribution zone with the same credibility. At the same time, rock mechanics parameters can be transplanted and calculated according to different geological layers based on the logging data of adjacent wells.

[0056] The formation fracture pressure is calculated using the Huang Rongzun method, and the calculation formula is formula (1).

[0057]

[0058] Where P f is the formation fracture pressure, in MPa; σ H Maximum horizontal in-situ stress, σ h is the minimum horizontal stress; f is the porosity; P p is the formation fracture pressure, MPa; S t is the tensile strength of the formation; μ is the Poisson's ratio; α is the effective stress coefficient.

[0059] Step 2: Correct the credible formation pore pressure in real time based on the logging while drilling data;

[0060] It should be noted that in step 2, by analyzing the execution process in step 1, The inversion calculation obtains the statistical results of the Eaton index distribution in the whole well section.

[0061] However, since the Eaton index changes with the well depth, and the method in step 1 performs probability statistics on the Eaton index of the entire well section to obtain the formation pressure distribution under different credibility conditions, although the calculation results have sufficient accuracy, for wells with large changes in the Eaton index along the well depth, the predicted credibility formation pressure distribution zone will be wider, which is not conducive to the wellbore structure design and risk avoidance of the narrow safety density window formation. Therefore, the Eaton index of the drilled formation can be re-inverted and calculated using the logging while drilling data to seek a reasonable method to correct the predicted pressure distribution zone of the lower undrilled formation.

[0062] Combination Figure 2 ,refer to Figure 4 , which is a flow chart of real-time correction of reliable formation pore pressure based on LWD data, mainly including the following steps:

[0063] (1) Calculation of formation pore pressure G based on seismic data p , Combined with the Eaton method to calculate the Eaton index, a large sample library n(h) is obtained, and the Eaton index of the entire well section is counted to obtain the distribution status;

[0064] (2) Based on the formation pore pressure G obtained by logging while drilling p ′, invert the Eaton index of the drilled section and obtain the small sample library n′(h 1 ), and n′(h 1 ) replaces the Eaton index n(h) of the drilled section 1 ) to form a new large sample library n′(h) and obtain a new distribution state; and then re-substitute the Eaton method to calculate the credible pore pressure of the lower undrilled formation.

[0065] Preferably, using the formula Calculate the formation fracture pressure P corresponding to the formation pore pressure at different probabilities under the condition of confidence J f ′, where σ h , σ H , α, μ, f and S t The rock mechanical parameters of the next geological layer are predicted by using the data from adjacent wells; then, when drilling to the preset distance Δh from the top of the next geological layer, the rock mechanical parameters x′(σ h ′、σ H ′, α′, μ′, f′, S t The average value of is the true value of the stratum, and uses Recalculate the formation fracture pressure P of the current geological layer f ″.

[0066] Preferably, the average value of each rock mechanical parameter in the well section Δh+δh of the geological layer measured by logging while drilling is The δh is the distance to be drilled when the drilling reaches the preset distance Δh from the top of the next geological layer;

[0067] when When In The average values ​​of the rock mechanical parameters in are replaced by And recalculate the formation fracture pressure p″′ of the geological layer f ,in, It is the average value of various rock mechanical parameters of the local geological layer measured by logging while drilling.

[0068] It should be noted that, through the above steps, a reliable formation pressure prediction method based on logging while drilling data is established. This method is used to perform real-time correction of the reliable formation pore pressure and formation fracture pressure of the lower undrilled formation based on the logging while drilling data. It not only has the advantages of the reliable formation pressure prediction method before drilling in step 1, but also can make up for the prediction error caused by insufficient abundance of adjacent well data, thereby improving the pressure prediction accuracy of the lower undrilled formation.

[0069] Step 3: Dynamic wellbore structure risk assessment during drilling.

[0070] In the process of performing step 3 of real-time correction of the reliable formation pore pressure based on the logging while drilling data, the specific execution process includes the following steps:

[0071] First, the distribution zone is determined based on the corrected credible formation pressure of the undrilled formation;

[0072] Specifically, based on the corrected credible formation pressure of the undrilled formation, a calculated value of the formation pressure is determined, wherein the calculated value of the formation pressure includes a credible distribution zone.

[0073] Then, based on the distribution band, a lower limit curve and an upper limit curve of a safe drilling fluid density window are determined.

[0074] Finally, the dynamic wellbore structure risk during drilling is evaluated.

[0075] First, a risk assessment model for the wellbore structure of the lower undrilled formation needs to be established;

[0076] Then, based on the wellbore structure risk assessment model of the lower undrilled formation, the dynamic wellbore structure risk during the drilling process is assessed;

[0077] The risk assessment model of the lower undrilled formation wellbore structure includes:

[0078] Kick risk: Risks of drill bit sticking due to differential pressure: Risk of leakage during drilling: R 井涌(h) , R 压差卡钻(h) , R 钻进井漏(h) are the risk of well kick, differential pressure sticking, and drilling leakage at well depth h; p(x) is the probability of event x; ρ 下 (h) and ρ 上 (h) are the equivalent densities corresponding to the lower limit curve and upper limit curve of the reliable safety drilling fluid density window at the well depth h; is the cumulative probability distribution of formation pore pressure at well depth h; is the cumulative probability distribution of formation fracture pressure at well depth h.

[0079] Through the above disclosed technical scheme, firstly, the credible formation pore pressure is predicted before drilling based on the seismic layer velocity; then the credible formation pore pressure is corrected in real time based on the logging while drilling data; finally, the dynamic wellbore structure risk is evaluated during the drilling process. The credible formation pore pressure is corrected in real time by the logging while drilling data to improve the pressure prediction accuracy of the lower undrilled formation, and a dynamic wellbore structure risk assessment method during the drilling process is established in combination with the safety density window constraint and probability theory, so as to perform a real-time quantitative assessment of the wellbore structure risk of the lower undrilled formation during the drilling process.

[0080] Further, based on the above steps 1 to 3, refer to Figure 5 .

[0081] Step 4: If there is a risk in the wellbore during the drilling process, redesign the wellbore structure;

[0082] If there is no risk to the wellbore during the drilling process, execute step 2 again.

[0083] It should be noted that, since a dynamic wellbore structure risk assessment can be obtained in the above embodiment, the assessment results can be used to determine whether there is a risk in the wellbore during the drilling process. If there is a risk, the wellbore structure is redesigned. If there is no risk, step 2 is re-executed to obtain the logging data while drilling and make real-time corrections to the credible formation pore pressure.

[0084] In the process of redesigning the wellbore structure, the specific implementation process is:

[0085] The established safe drilling fluid density window constraint condition includes:

[0086] Among them, ρ pmax ′ is the maximum formation pore pressure gradient in the lower undrilled formation pressure prediction section after correction based on the measurement while drilling data, ρ pmin ′ is the minimum formation pore pressure gradient in the lower undrilled formation pressure prediction section after correction based on the measurement while drilling data, ρ fmin ′ is the minimum formation fracture pressure gradient in the lower undrilled formation pressure prediction section after correction based on the measurement while drilling data, S b ′ is the suction pressure coefficient calculated based on the real-time wellbore structure and drilling conditions, S g ′ is the excitation pressure coefficient calculated based on the real-time wellbore structure and drilling conditions, and Δρ′ is the additional drilling fluid density calculated based on the real-time wellbore structure and drilling conditions.

[0087] In order to facilitate the understanding of the above scheme, the following is a further introduction to this scheme:

[0088] This application proposes a new method for optimizing the design of dynamic wellbore structure during drilling based on while-drilling data, which fully utilizes the advantages of technologies such as logging while drilling to seek methods to improve the prediction accuracy of formation pressure in a narrow safety density window, eliminates potential risks caused by formation uncertainty parameters from the root, and on this basis studies the identification methods of engineering risks such as leakage, blowout, collapse, and sticking during drilling, and establishes a dynamic wellbore structure risk assessment method during drilling; at the same time, studies the uncertainty parameters in existing wellbore structure design methods, improves the design methods, and thus minimizes the risks of wellbore structure design.

[0089] The technical solution is:

[0090] Firstly, the formation pressure of the target deep well with complex formation is predicted with credibility using seismic data, and the pressure of the drilled formation is corrected with the LWD data, and then the pressure of the lower undrilled formation is re-predicted; then, based on the confidence-based safe drilling fluid density window corrected by the LWD data, the risk assessment of the existing wellbore structure design scheme can be carried out according to the pressure balance constraint condition; at the same time, if the risk assessment method is used to predict that the existing wellbore structure design scheme of the lower undrilled formation has a large risk during the drilling process, it should be adjusted to avoid the risk. Therefore, a dynamic wellbore structure design method based on LWD data is proposed during the drilling process.

[0091] The main steps are:

[0092] Step 1: Pre-drilling reliable formation pressure prediction based on seismic layer velocity;

[0093] Step 2: Real-time correction of formation pressure with credibility based on logging while drilling data;

[0094] Step 3: Dynamic wellbore structure risk assessment during drilling;

[0095] Step 4: Dynamic wellbore structure optimization design during drilling.

[0096] The specific implementation process of each step:

[0097] Step 1: Pre-drilling reliable prediction of formation pressure based on seismic interval velocity.

[0098] In order to fully consider the uncertainty of formation parameters in deep wells with complex formations, Professor Guan Zhichuan and others proposed a method for predicting formation pressure based on probability statistics [Ke Ke, Guan Zhichuan, Zhou Xing. Credible method for establishing formation pore pressure before drilling deep wells with complex formations [J]. Journal of China University of Petroleum (Natural Science Edition), 2009, 33(5): 61-67.]. Starting from the principle of this method, seismic data are used to predict the formation pressure of the target deep well with complex formations with credibility, and the drilled formation pressure is corrected in combination with the logging data while drilling, and then the pressure of the lower undrilled formation is re-predicted. The seismic layer velocity ratio is used to predict the target well pressure using the logging data of adjacent wells. A very important advantage is that it is not affected by the abundance of adjacent well data. At the same time, it is conducive to combining the logging data while drilling such as MWD and LWD to correct the pressure of the drilled formation and related calculation parameters. This method uses the Eaton method, Fillippone method and effective stress method to jointly calculate the formation pore pressure. The specific process is as follows: Figure 2 shown.

[0099] The formation fracture pressure is calculated using the Huang Rongzun method, and the calculation formula is formula (1).

[0100]

[0101] Where P f is the formation fracture pressure, MPa; σ H and σ h is the maximum and minimum horizontal stress, MPa; f is the porosity, %; P p is the formation fracture pressure, MPa; S t is the formation tensile strength, MPa; μ is Poisson’s ratio, dimensionless; α is the effective stress coefficient, dimensionless.

[0102] The calculation of formation breakdown pressure requires the use of formation pore pressure. Therefore, the calculated value of formation breakdown pressure also contains a distribution zone with the same credibility. At the same time, the rock mechanics parameters in the formula can be transplanted and calculated according to different geological stratifications using the logging data of adjacent wells.

[0103] Step 2: Real-time correction of formation pressure with credibility based on LWD data.

[0104] From the analysis of the pre-drilling reliable formation pressure prediction method based on seismic layer velocity in step 1, we can see that the process Figure 1 The Eaton index distribution obtained by inversion of formula (2) is the statistical result of the whole well section, as shown in formula (3) and Figure 3 .

[0105]

[0106]

[0107] Since the Eaton index changes with the well depth, the method in step 1 performs probability statistics on the Eaton index of the entire well section to obtain the formation pressure distribution under different credibility conditions. Although the calculation results have sufficient accuracy, for wells with large changes in the Eaton index along the well depth, the predicted credibility formation pressure distribution zone will be wider, which is not conducive to the wellbore structure design and risk avoidance of the narrow safety density window formation. Therefore, the Eaton index of the drilled formation can be re-inverted and calculated using the logging while drilling data to find a reasonable method to correct the predicted pressure distribution zone of the lower undrilled formation.

[0108] Assume that the Eaton index obtained by inversion based on the seismic layer velocity before drilling using formula (2) is a large sample library n(h), where h is the depth of the target well, m; the depth of the drilled section is h 1 , the formation pore pressure obtained by logging while drilling is G p ′, g / cm 3 , then the Eaton index of the drilled formation can be corrected according to formula (4):

[0109]

[0110] In the formula, G h is the hydrostatic pressure, g / cm 3 ; G 0 is the pressure gradient of the overburden, g / cm 3 ; V n is the layer velocity under normal compaction conditions, m / s; V in is the layer velocity, m / s.

[0111] The Eaton index of the drilled formation corrected by the LWD data is regarded as a small sample library n′(h 1 ), and according to the previous assumption, the Eaton index of the entire well section obtained based on the seismic layer velocity inversion before drilling is a large sample library n(h), where 0-h 1 The Eaton index of the well section (drilled section) is the small sample library n(h 1 ), n′(h 1 ) replace n(h 1 ) to form a new large sample library n′(h), then the distribution form of the Eaton index in the new large sample library can be obtained by formula (5).

[0112]

[0113] Therefore, the distribution zone of the pore pressure in the lower undrilled formation with credibility can be corrected in real time according to the modified Eaton index distribution form and the method in step 1. The specific process is as follows: Figure 3 shown.

[0114] As for the formation breakdown pressure, it can be known from formula (1) that it can be corrected in real time with the correction of the formation pore pressure; at the same time, its calculation model involves many rock mechanics parameters, which are related to geological stratification, etc. In previous calculations, the regional transplantation prediction is generally carried out based on the logging data of adjacent wells, and the same geological stratification is regarded as a constant for calculation, so its value is uncertain. In order to obtain a more accurate prediction value of the formation breakdown pressure, the logging data while drilling can be used for correction. The specific steps are as follows:

[0115] (1) Based on the real-time correction value of the formation pore pressure, the formation pore pressure P at different probabilities under the condition of credibility J is calculated using formula (1): p ′Corresponding formation fracture pressure P f ′, as shown in formula (6):

[0116]

[0117] (2) If the rock mechanical parameters of the next geological layer predicted by adjacent well data before drilling are x(σ h , σH ,α,μ,f,S t ), when drilling to the distance Δh (the step length is set according to the actual situation) from the top of the next geological layer, it is considered that the rock mechanical parameters x′(σ h ′、σ H ′, α′, μ′, f′, S t The average value of is the true value of the layer, and the formation fracture pressure P of the local geological layer is recalculated using formula (7): f ″:

[0118]

[0119] (3) If drilling continues for δh, the average value of each rock mechanical parameter in the well section of the geological layer Δh+δh is measured by logging while drilling: When |x″-x′|>ε, use Replace (7) Recalculate the formation fracture pressure P″′ of the geological layer f ;

[0120] (4) Repeat step (3) until all the local geological layers are drilled.

[0121] Therefore, a reliable formation pressure prediction method based on LWD data was established. This method can be used to correct the reliable formation pore pressure and formation fracture pressure of the lower undrilled formation based on LWD data. It not only has the advantages of the reliable formation pressure prediction method before drilling in step one, but also can make up for the prediction error caused by insufficient abundance of adjacent well data, thereby improving the pressure prediction accuracy of the lower undrilled formation.

[0122] Step 3: Dynamic wellbore structure risk assessment during drilling.

[0123] Step 2 establishes a reliable formation pressure prediction method based on LWD data, which can correct the reliable formation pressure prediction value of the lower undrilled formation as the drilling depth increases, so the safe drilling fluid density window of the lower undrilled formation is also corrected in real time. Since the formation pressure profile established in step 1 is a reliable distribution zone, if the reliability J = 95% - 5% = 90% is selected, the formation pore pressure profile corresponding to the cumulative probability of 95% is defined as the lower limit curve of the safe drilling fluid density window, and the formation fracture pressure profile corresponding to the cumulative probability of 5% is defined as the upper limit curve of the safe drilling fluid density window, thus forming a safe drilling fluid density window with reliability J.

[0124] In the reliable safe drilling fluid density window established in step 2 based on the LWD data, the risk assessment of the existing wellbore structure design can be performed according to the pressure balance constraint. In order to ensure the safety of the open hole section, the following pressure balance constraints must be met:

[0125] Stop pump to prevent well surge:

[0126] ρ m (H i )≥ρ pmax +S b +Δρ (8)

[0127] Differential Pressure Tubing:

[0128] (ρ m (H i )-ρ pmin )×H pmin ×0.00981≤ΔP (9)

[0129] Drilling leak prevention:

[0130] ρ m (H i )+S g +S f ≤ρ fmin (10)

[0131] Leakage prevention when closing the well:

[0132]

[0133] Among them, H i is the depth of the calculation point, m; S b is the suction pressure coefficient, g / cm 3 ; S k is the allowable amount of well kick, g / cm 3 ; S g is the excitation pressure coefficient, g / cm 3 ρ m (H i ) is the static equivalent density of drilling fluid, g / cm 3 ρ pmax The maximum value of the formation pore pressure at the calculation point and above (the lower limit curve of the safe drilling fluid density window), g / cm 3 ρ pmin The minimum value of the formation pore pressure at and above the calculation point (the lower limit curve of the safe drilling fluid density window), g / cm 3 ; ΔP represents the allowable value of differential pressure for drilling, MPa; S f is the safety factor of formation fracture pressure, g / cm 3 ; Δρ is the additional drilling fluid density, g / cm3 ρ fmin The minimum value of the formation breakdown pressure (upper limit curve of the safe drilling fluid density window) at the calculation point and above the well section, g / cm 3 ;H pmin is the well depth where the formation pore pressure is minimum, m; H n-1 is the depth of the casing shoe of the previous casing, m.

[0134] Since the kick allowance S k and formation fracture pressure safety factor S f They are all safety factors added artificially due to inaccurate prediction of formation pressure, which represent the uncertainty of formation pressure. In the safe drilling fluid density window with credibility J, it is believed that the prediction of formation pressure is sufficiently accurate and reliable. Therefore, the kick allowance S can be used as k and formation fracture pressure safety factor S f Ignore, and then the equation (11) in the pressure balance constraint can be ignored, and equation (10) becomes:

[0135] Drilling leak prevention:

[0136] ρ m (H i )+S g ≤ρ fmin (12)

[0137] Therefore, equations (8), (9) and (12) constitute the pressure balance constraint conditions under the credibility J condition.

[0138] If the design drilling fluid density of the lower undrilled formation in the existing wellbore structure design satisfies equations (8), (9) and (12), it is considered that the current wellbore structure design has no engineering risks such as leakage, blowout and collapse. If not, the risk R at the well depth h can be calculated as follows: 井涌 / 压差卡钻 / 钻进井漏(h) Conduct quantitative assessment.

[0139] Kick risk:

[0140]

[0141] Risks of drill bit sticking due to differential pressure:

[0142]

[0143] Risk of lost circulation during drilling:

[0144]

[0145] In the formula, R 井涌(h) , R 压差卡钻(h) , R 钻进井漏(h)are the risk of well kick, differential pressure sticking, and drilling leakage at well depth h, respectively; p(x) is the probability of event x; ρ 下 (h) and ρ 上 (h) are the equivalent densities corresponding to the lower and upper limit curves of the reliable safety drilling fluid density window at the well depth h, g / cm 3 ; is the cumulative probability distribution of formation pore pressure at well depth h; is the cumulative probability distribution of formation fracture pressure at well depth h.

[0146] In the lower undrilled formation wellbore structure risk assessment model composed of equations (13), (14), and (15), ρ 下 (h) and ρ 上 (h) is updated in real time according to the logging while drilling data using the method in step 1; therefore, a dynamic risk assessment of the existing wellbore structure design scheme can be performed during the drilling process. If the assessment result indicates a high engineering risk, the existing wellbore structure design scheme should be adjusted and the risk assessment should be re-performed until the pressure balance constraint condition under the credibility condition J is met.

[0147] Step 4: Dynamic wellbore structure optimization design during drilling.

[0148] Previously, a pre-drilling wellbore structure design method was established based on the pre-drilling credible formation pressure prediction profile and with equations (8), (9), and (12) as safety density window constraints. This method improves the reliability of the pre-drilling wellbore structure design results, thereby reducing the potential risks of the pre-drilling wellbore structure design scheme. However, through the analysis of step one, although the pre-drilling credible formation pressure prediction method can improve the reliability of formation pressure prediction, for deep wells with complex formations where the abundance of adjacent well data is not high, it is still necessary to use the downhole logging data to make real-time corrections to maximize the prediction accuracy of formation pressure; at the same time, if the method in step three is used to predict that the existing wellbore structure design scheme for the lower undrilled formation has a large risk during the drilling process, it should be adjusted to avoid the risk. Therefore, this paper proposes a dynamic wellbore structure design method during drilling based on downhole logging. The process is as follows: Figure 4 shown.

[0149] Among them, the new safe drilling fluid density window constraint condition * as follows:

[0150]

[0151] In the formula, ρ pmax ′、ρ pmin ′、ρ fmin ′、S b ′、S g′ and Δρ′ are no longer constant values, but variables that change with the drilling process. pmax ′、ρ pmin ′、ρ fmin ′ are the maximum formation pore pressure gradient, minimum formation pore pressure gradient and minimum formation fracture pressure gradient in the lower undrilled formation pressure prediction profile after correction based on the measurement while drilling data, g / cm 3 ; S b ′、S g ′ and Δρ′ are the suction pressure coefficient, agitation pressure coefficient and additional drilling fluid density calculated based on the real-time wellbore structure and drilling conditions, g / cm 3 .

[0152] This method uses the logging while drilling data to make real-time corrections to the reliable formation pressure profile of the lower undrilled formation, and calculates the drilling fluid additional density Δρ and the agitation pressure coefficient S in real time according to the drilling depth and working conditions. g and suction pressure coefficient S b , thereby determining the new safety density window constraint condition (Equation (16)). On this basis, the risk of the lower undrilled formation is quantitatively evaluated using the method in step 3. Once a higher risk is found, the wellbore structure design of the lower formation is redesigned in a timely manner, thereby performing real-time dynamic wellbore structure design of the lower undrilled formation during the drilling process, thereby avoiding engineering risks to the greatest extent at the design level.

[0153] Beneficial effects:

[0154] 1. A reliable formation pressure prediction method based on LWD data was established. This method can correct the reliable pressure distribution zone of the lower undrilled formation in real time according to the LWD data, thus improving the pressure prediction accuracy of the lower undrilled formation.

[0155] 2. Based on the reliable formation pressure prediction method based on LWD data, combined with the safety density window constraint and probability theory, a dynamic wellbore structure risk assessment method during drilling was established, which can conduct real-time quantitative assessment of the wellbore structure risk of the lower undrilled formation during drilling;

[0156] 3. A dynamic wellbore structure design method during drilling is proposed, which can perform real-time dynamic wellbore structure design on the lower undrilled formation during drilling, thereby avoiding engineering risks to the greatest extent at the design level.

[0157] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0158] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0159] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A dynamic wellbore structure optimization design method during drilling based on drilling data, characterized in that: include: Step 1: Pre-drilling reliable formation pore pressure prediction based on seismic interval velocity; Step 2: Correct the credible formation pore pressure in real time based on the LWD data, including: (1) Calculation of formation pore pressure G based on seismic data p , Combined with the Eaton method to calculate the Eaton index, a large sample library n(h) is obtained, and the Eaton index of the entire well section is counted to obtain the distribution status; (2) Based on the formation pore pressure G obtained by logging while drilling p ′, invert the Eaton index of the drilled section to obtain a small sample library n′(h)1, and replace the Eaton index n(h1) of the drilled section with n′(h)1 to form a new large sample library n′(h) to obtain a new distribution state; re-substitute the Eaton method to calculate the credibility pore pressure of the lower undrilled formation; (3) Using the formula Calculate the formation fracture pressure P corresponding to the formation pore pressure at different probabilities under the condition of confidence J f ′, where σ h , σ H , α, μ, f and S t To predict the rock mechanical parameters of the next geological layer using the data from adjacent wells; When drilling to the preset distance Δh from the top of the next geological layer, the average value of each rock mechanical parameter x′ in the current geological layer obtained by logging while drilling is the true value of the layer, where x′ includes σ h ′、σ H ′, α′, μ′, f′ and S t ', said include and And use Recalculate the formation fracture pressure P of the current geological layer f ″; Step 3: Dynamic wellbore structure risk assessment during drilling.

2. The method according to claim 1, characterized in that The prediction of formation pore pressure with credibility before drilling based on seismic layer velocity in step 1 includes: Based on the acquired seismic layer velocity data, preprocessing the seismic layer velocity data to determine the overlying rock pressure gradient; Calculate formation pore pressure based on Fillippone method; Inversely calculate the Eaton index in combination with the Eaton method, and obtain the distribution state based on the Eaton index; Re-substitute the Eaton method to calculate the reliable formation pore pressure.

3. The method according to claim 1, characterized in that: Step 2 is to utilize Recalculate the formation fracture pressure P of the current geological layer f "After that, it also includes: (4) The average value of each rock mechanical parameter in the well section Δh+δh of the geological layer is measured by logging while drilling. The δh is the distance to be drilled when the drilling reaches the preset distance Δh from the top of the next geological layer; when When In Replace with And recalculate the formation fracture pressure p of the geological layer f "',in, The average values ​​of rock mechanical parameters of the local geological layers measured by logging while drilling include and 4. The method according to claim 1, characterized in that: In step 3, the dynamic wellbore structure risk assessment during drilling includes: Determine the distribution zone based on the corrected credible formation pressure of the undrilled formation; Based on the distribution zone, determining a lower limit curve and an upper limit curve of a safe drilling fluid density window; Risk assessment of dynamic wellbore structure during drilling.

5. The method according to claim 4, characterized in that The method of determining the distribution zone of the credible formation pore pressure based on the corrected undrilled formation comprises: Based on the corrected credible formation pressure of the undrilled formation, a calculated value of the formation pressure is determined, wherein the calculated value of the formation pressure includes a credible distribution zone.

6. The method according to claim 4, characterized in that The risk assessment of dynamic wellbore structure during drilling includes: Based on the pre-established wellbore structure risk assessment model for the lower undrilled formation, the dynamic wellbore structure risk assessment during the drilling process is performed; The risk assessment model of the wellbore structure of the lower undrilled formation includes: well kick risk: Risks of drill bit sticking due to differential pressure: Risk of drilling leakage: R 井涌(h) , R 压差卡钻(h) , R 钻进井漏(h) are the risk of well kick, differential pressure sticking, and drilling leakage at well depth h; p(x) is the probability of event x; ρ 下 (h) and ρ 上 (h) are the equivalent densities corresponding to the lower limit curve and upper limit curve of the reliable safety drilling fluid density window at the well depth h; is the cumulative probability distribution of formation pore pressure at well depth h; F ρf(h) (x) is the cumulative probability distribution of formation fracture pressure at well depth h.

7. The method according to claim 1, characterized in that After executing step 3, dynamic wellbore structure risk assessment during drilling, it also includes: Step 4: If there is a risk in the wellbore during the drilling process, redesign the wellbore structure; If there is no risk in the wellbore during the drilling process, execute step 2.

8. The method according to claim 7, characterized in that In step 4, if there is a risk in the wellbore during the drilling process, redesigning the wellbore structure includes: If there is a risk in the wellbore during the drilling process, a safe drilling fluid density window constraint condition is established; The safe drilling fluid density window constraint conditions include: Among them, ρ pmax is the maximum formation pore pressure gradient in the lower undrilled formation pressure prediction section after correction based on the measurement while drilling data, ρ pmin ′ is the minimum formation pore pressure gradient in the lower undrilled formation pressure prediction section after correction based on the measurement while drilling data, ρ fmin ′ is the minimum formation fracture pressure gradient in the lower undrilled formation pressure prediction section after correction based on the measurement while drilling data, S b ′ is the suction pressure coefficient calculated based on the real-time wellbore structure and drilling conditions, S g ′ is the excitation pressure coefficient calculated based on the real-time wellbore structure and drilling conditions, and △ρ′ is the additional drilling fluid density calculated based on the real-time wellbore structure and drilling conditions.

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