Method and system for regulating and controlling drilling fluid density of pre-exploratory well while drilling

Abstract

The invention provides a method and a system for regulating and controlling drilling fluid density of a pre-exploratory well while drilling, and relates to the technical field of safety monitoring of petroleum and natural gas drilling. According to the method provided by the invention, the corrected Dc index, the formation pore pressure gradient, the formation fracture pressure gradient and the rock anti-drilling strength of the pre-exploratory well can be determined by acquiring the drilling parameter data of the drilled section; then, the drilling fluid density safety margin weight of the pre-exploratory well at the first well depth is determined according to the corrected Dc index of the pre-exploratory well and the rock anti-drilling strength; according to the formation pore pressure gradient, the formation fracture pressure gradient and the drilling fluid density safety margin weight of the pre-exploratory well in the first well depth, the drilling fluid target density of the pre-exploratory well is determined; the drilling fluid density of the pre-exploratory well is adjusted to the target drilling fluid density; according to the method provided by the invention, the density of the drilling fluid can be accurately controlled, so that complex risks of well leakage and well kick accidents are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of safety monitoring of oil and gas drilling, and in particular to a method and system for regulating the density of drilling fluid in a pre-exploration well while drilling. Background Art

[0002] During the drilling process, the density of the drilling fluid needs to be controlled to ensure the balance of the bottom hole pressure and prevent well kicks and well leakage accidents during the drilling process. Pre-exploration wells are a type of drilling carried out for the purpose of confirming the location and properties of underground oil and gas. Due to the small number of wells drilled in the block where the pre-exploration well is located and the scarcity of reference data from adjacent wells, the uncertainty of the wellbore pressure profile of the pre-exploration well is large, and the wellbore pressure control and drilling fluid density control during the drilling process are difficult, which is prone to well control and well leakage risks, bringing huge challenges to the safe drilling of pre-exploration wells.

[0003] For pre-exploration wells, related technologies usually rely on seismic data to predict formation pore pressure and formation fracture pressure profiles to establish a wellbore drilling fluid density window. However, this method is limited by the accuracy of seismic data, resulting in large errors in the predicted drilling fluid density window, and the density window cannot be updated in real time during the drilling process. The drilling fluid density can only be regulated based on the drilling site experience. The lack of scientific data support leads to frequent well leakage and well kick accidents during the drilling process, which lengthens the drilling cycle and increases the drilling cost. CN116244938A proposes a method for optimizing the design of drilling fluid density in mud shale formations. The specific process includes obtaining the physical property parameters of mud shale cores; establishing a mechanical model of wellbore instability containing a weak surface structure according to the wellbore instability mechanism; judging the collapse of the rock around the well according to the Mohr-Coulomb failure criterion and the weak surface failure criterion, and determining the minimum drilling fluid density and the maximum drilling fluid density for maintaining the wellbore stability of the mud shale formation in combination with the allowable collapse degree of the project; fitting the relationship between the mechanical drilling speed and the static liquid column pressure of the mud shale formation at different depths, and calculating the upper limit of the drilling fluid density at the critical mechanical drilling speed; and obtaining the design range of the drilling fluid density window for the mud shale formation considering the wellbore stability and rapid drilling according to the minimum drilling fluid density, the maximum drilling fluid density and the upper limit of the drilling fluid density at the critical mechanical drilling speed. The above method is used to obtain the lower limit of drilling fluid density that meets the allowable collapse degree of the project and the upper limit of drilling fluid density for the optimal mechanical drilling speed. The lower limit of drilling fluid density that meets the allowable collapse degree of the project and the optimal mechanical drilling speed are determined by considering the maximum allowable wellbore collapse degree and the maximum mechanical drilling speed. However, this method still belongs to static design analysis and cannot update the drilling fluid density window and adjust the drilling fluid density according to the actual drilling information during the actual drilling process. CN109509111A proposes to calculate the rock density curve that has not been tested by shallow logging and splice it with the density curve obtained by logging to obtain the density curve from the surface to the deep reservoir section; calculate the overlying formation pressure and hydrostatic pressure based on the density curve; calculate the formation pressure of the shallow clastic rock formation; calculate the formation pressure of the gas-bearing shale reservoir; calculate the formation pressure of the carbonate reservoir; in the above steps, different pressure prediction models are used for different lithologies to improve the formation pressure prediction accuracy. However, this method still predicts formation pressure based on logging data of adjacent wells before drilling, and is not suitable for the situation where there is a lack of logging data of adjacent wells in the pre-exploration well. At the same time, the drilling fluid density cannot be updated and adjusted based on the actual drilling information during the drilling process.

[0004] Therefore, a method and system for regulating the density of drilling fluid in a pre-exploration well while drilling is urgently needed to realize real-time updating of the safe drilling fluid density window of the pre-exploration well during the drilling process, and then realize precise regulation of the drilling fluid density, thereby reducing the complex risks of well leakage and well kick accidents. Summary of the invention

[0005] The embodiment of the present invention provides a method and system for regulating the density of drilling fluid in a pre-exploration well while drilling, which can realize real-time updating of the safe drilling fluid density window of the pre-exploration well during the drilling process, and then realize precise regulation of the drilling fluid density, thereby reducing the complex risks of well leakage and well kick accidents.

[0006] To achieve the above object, the embodiments of the present invention adopt the following technical solutions:

[0007] In a first aspect, a method for controlling the density of drilling fluid in a pre-exploration well while drilling is provided, the method comprising: obtaining drilling parameter data of a drilled section, the parameter data including mechanical drilling speed, drill bit speed, drilling pressure, drill bit diameter, formation water density and actual drilling fluid density corresponding to different well depths; determining a modified Dc index corresponding to different well depths according to the drilling parameter data of the drilled section; determining a vertical stress gradient of the pre-exploration well according to the modified Dc index corresponding to different well depths, wherein the well of the drilled section is located in the pre-exploration well; determining the formation of the pre-exploration well according to the vertical stress gradient of the pre-exploration well. Pore ​​pressure gradient and formation fracture pressure gradient; determine the rock drilling resistance of the pre-exploration well according to the drilling parameter data of the drilled section; determine the drilling fluid density safety margin weight of the pre-exploration well at the first well depth according to the modified Dc index and rock drilling resistance of the pre-exploration well; determine the drilling fluid target density of the pre-exploration well according to the formation pore pressure gradient, formation fracture pressure gradient and drilling fluid density safety margin weight of the pre-exploration well at the first well depth; adjust the drilling fluid density of the pre-exploration well to the drilling fluid target density; the formula for determining the drilling fluid density safety margin weight of the pre-exploration well at the first well depth is:

[0008]

[0009] Where w is the safety margin weight of drilling fluid density; S n+1 is the rock drilling resistance of the exploration well at the first depth, S n Dc is the rock drilling resistance of the exploration well at the second well depth; n+1 is the modified Dc index of the pilot well at the first depth, Dc n is the modified Dc index of the exploration well at the second well depth, w n+1 is the safety margin weight of drilling fluid density at the first well depth of the pre-exploration well; w n is the safety margin weight of the drilling fluid density of the pre-exploration well at the second well depth; the first well depth is greater than the second well depth; ζ1, ζ2, ζ3 are model coefficients.

[0010] In a possible implementation manner of the first aspect, a formula for determining the modified Dc index Dc is:

[0011]

[0012] Among them, ROP is the mechanical drilling speed, in m / h; RPM is the drill bit speed, in r / min; WOB is the drilling pressure, in kN; d b is the drill bit diameter, in mm; ρ w is the formation water density, in g / cm 3 , the value is 1.05g / cm 3 ρ 钻井液 The actual drilling fluid density of the drilled section, in g / cm 3 .

[0013] In a possible implementation of the first aspect, determining the vertical stress gradient of the exploration well according to the modified Dc index corresponding to different well depths includes:

[0014] Determine the formation porosity based on the modified Dc index corresponding to different well depths;

[0015] Determine the density of formation rocks based on formation porosity;

[0016] Determine the vertical stress gradient of the pilot well according to the rock density of the formation;

[0017] The formula for determining the formation porosity φ is the first formula or the second formula. The first formula is:

[0018] φ=aexp (b×Dc) ;

[0019] a and b are model coefficients;

[0020] The second formula is:

[0021]

[0022] Among them, A, B, λ and k are model coefficients, and md is the well depth in meters.

[0023] In a possible implementation of the first aspect, a formula for determining the formation rock density ρ is:

[0024] ρ=ρ matrix (1-φ)+ρ w φ;

[0025] ρ matrix is the rock skeleton density, in g / cm 3 ;

[0026] Vertical stress gradient ρ v The formula for determining is:

[0027]

[0028] ρ v =σv ×0.00981 / TVD;

[0029] σ v is the vertical stress, in MPa; g is the gravitational acceleration, in m / s 2 ; ρ is the rock density of the calculated well section dTVD formation, in g / cm 3 ; TVD1 is the starting vertical depth, the unit is m, and the value is 0; TVD2 is the ending vertical depth, the unit is m, and TVD is the vertical depth of the calculation point, the unit is m.

[0030] In a possible implementation of the first aspect, determining a formation pore pressure gradient and a formation fracture pressure gradient of the exploration well according to a vertical stress gradient of the exploration well includes:

[0031] Determine the formation pore pressure corresponding to different well depths of the exploration well according to the vertical stress gradient of the exploration well;

[0032] Determine the formation pore pressure gradient of the exploration well according to the formation pore pressure and vertical stress gradient corresponding to different well depths of the exploration well;

[0033] Determine the formation fracture pressure gradient of the exploration well according to the formation pore pressure gradient of the exploration well;

[0034] The formula for determining formation pore pressure is:

[0035] σ e =σ vA -P pA =σ vB -P pB ;

[0036] P pB =P pA -(σ vA -σ vB );

[0037] Among them, σ e Effective overburden pressure, in MPa; σ vA The vertical stress at the well depth A is in MPa; P pA The formation pore pressure at the well depth A, in MPa; σ vB The vertical stress at the well depth B is in MPa; P pB The formation pore pressure at the well depth B, in MPa;

[0038] Formation pore pressure gradient ρ of the pilot well p The formula for determining is:

[0039] ρ p =P p / (0.00981×TVD);

[0040] Among them, P p is the formation pore pressure, in MPa;

[0041] Formation fracture pressure gradient ρ of the pilot well f The determination formula is the third formula or the fourth formula;

[0042] The third formula is:

[0043]

[0044] Wherein, μ is the Poisson’s ratio of the formation rock, dimensionless;

[0045] The fourth formula is:

[0046] ρ f =k1+k2(P p -P n ) / (TVD*0.00981);

[0047] P n =1.05×0.00981×TVD;

[0048] k1 and k2 are model coefficients; P n The pore pressure of the formation under normal compaction conditions, in MPa.

[0049] In a possible implementation of the first aspect, a formula for determining the rock anti-drilling strength S of the pilot well is:

[0050] S=2×WOB / (d b ×ROP / RPM)

[0051] Among them, RPM is the drill speed.

[0052] In a possible implementation of the first aspect, determining a target density of drilling fluid in the pilot well according to a formation pore pressure gradient, a formation fracture pressure gradient, and a drilling fluid density safety margin weight of the pilot well at a first well depth includes:

[0053] Determine the drilling fluid safety density window of the pre-exploration well according to the formation pore pressure gradient, formation fracture pressure gradient and drilling fluid density safety margin weight of the pre-exploration well;

[0054] Determine the drilling fluid target density of the pre-exploration well according to the drilling fluid safety density window and the drilling fluid density safety margin weight of the pre-exploration well;

[0055] The formula for determining the drilling fluid safety density window △ρ is:

[0056] Δρ=ρ f -ρ p=(1-w)Δρ 上 +wΔρ 下 =(1-w)ρ f -wρ p +(2w-1)ρ 钻井液 ;

[0057] Δρ 上 =ρ f -ρ 钻井液 ;

[0058] Δρ 下 =ρ 钻井液 -ρ p ;

[0059] Among them, △ρ 上 is the upper boundary safety margin; △ρ 下 is the lower boundary safety margin.

[0060] In a possible implementation of the first aspect, the drilling fluid target density ρ 目标密度 The formula for determining is:

[0061]

[0062] The beneficial effects of the present invention are as follows: the method provided by the present invention can determine the safe drilling fluid density window of the pre-exploration well and the drilling fluid density corresponding to the pre-exploration well at different well depths by acquiring the drilling parameter data of the drilled section, thereby realizing accurate control of the drilling fluid density, thereby reducing the complicated risks of well leakage and well kick accidents. In other words, the method provided by the present invention aims at the problems of little drilling data for the pre-exploration well, low accuracy in establishing the safe density window through seismic data, and high risk of well kick and well leakage due to the use of inappropriate drilling fluid density during the drilling process. A method for determining the safe density window while drilling and controlling the drilling fluid density that does not rely on logging and seismic data is proposed, which improves the ability to control the wellbore pressure during the drilling of the pre-exploration well, and provides an effective technical solution for reducing the risk of well leakage and well kick during the drilling of the pre-exploration well.

[0063] In a second aspect, an embodiment of the present invention provides a drilling fluid density while-drilling control system for a pre-exploration well, the system comprising: a data acquisition module for acquiring drilling parameter data of a drilled section, the parameter data including mechanical drilling speed, drill bit speed, drilling pressure, drill bit diameter, formation water density and actual drilling fluid density corresponding to different well depths; an index determination module for determining a modified Dc index corresponding to different well depths according to the drilling parameter data of the drilled section; a stress determination module for determining a vertical stress gradient of the pre-exploration well according to the modified Dc index corresponding to different well depths, wherein the drilling of the drilled section is located in the pre-exploration well; a pressure determination module for determining a vertical stress gradient of the pre-exploration well according to the modified Dc index corresponding to different well depths. The vertical stress gradient of the exploration well determines the formation pore pressure gradient and formation fracture pressure gradient of the pre-exploration well; the strength determination module is used to determine the rock drilling resistance strength of the pre-exploration well according to the drilling parameter data of the drilled section; the weight determination module is used to determine the drilling fluid density safety margin weight of the pre-exploration well at the first well depth according to the modified Dc index and rock drilling resistance strength of the pre-exploration well; the density determination module is used to determine the drilling fluid target density of the pre-exploration well according to the formation pore pressure gradient, formation fracture pressure gradient and drilling fluid density safety margin weight of the pre-exploration well at the first well depth; the density control module is used to adjust the drilling fluid density of the pre-exploration well to the drilling fluid target density;

[0064] The formula for determining the safety margin weight of the drilling fluid density of the pilot well at the first well depth is:

[0065]

[0066] Where w is the safety margin weight of drilling fluid density; S n+1 is the rock drilling resistance of the exploration well at the first depth, S n Dc is the rock drilling resistance of the exploration well at the second well depth; n+1 is the modified Dc index of the pilot well at the first depth, Dc n is the modified Dc index of the exploration well at the second well depth, w n+1 is the safety margin weight of drilling fluid density at the first well depth of the pre-exploration well; w n is the safety margin weight of the drilling fluid density of the pre-exploration well at the second well depth; the first well depth is greater than the second well depth; ζ1, ζ2, ζ3 are model coefficients.

[0067] According to a third aspect, an electronic device is provided, comprising a memory and one or more processors; the memory is coupled to the processor; wherein the memory stores computer program code, the computer program code comprises computer instructions, and when the computer instructions are executed by the processor, the electronic device executes a method as in any implementation of the first aspect.

[0068] According to a fourth aspect, a computer-readable storage medium is provided, comprising computer instructions. When the computer instructions are executed on an electronic device, the electronic device executes the method in any implementation of the first aspect.

[0069] According to a fifth aspect, a computer program product is provided. When the computer program product is run on a computer, the computer is enabled to execute the method in any implementation of the first aspect.

[0070] It can be understood that the beneficial effects that can be achieved by the system of the second aspect, the electronic device of the third aspect, the computer-readable storage medium of the fourth aspect, and the computer program product of the fifth aspect provided above can be referred to the beneficial effects in the first aspect and any possible design method thereof, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 A schematic diagram of the hardware structure of an electronic device shown in an embodiment of the present invention;

[0072] Figure 2 A flow chart of a method for controlling the density of drilling fluid in a prospecting well while drilling is shown in an embodiment of the present invention;

[0073] Figure 3 A data diagram of a modified Dc index of a prospecting well shown in an embodiment of the present invention;

[0074] Figure 4 A flow chart of another method for controlling the density of drilling fluid in a prospecting well while drilling is shown in an embodiment of the present invention;

[0075] Figure 5 A data diagram of formation rock density of a pre-exploration well shown in an embodiment of the present invention;

[0076] Figure 6 A data diagram of a vertical stress gradient of a formation in a pre-exploration well shown in an embodiment of the present invention;

[0077] Figure 7 A data diagram of a formation pore pressure gradient of a pre-exploration well shown in an embodiment of the present invention;

[0078] Figure 8 A data diagram of a formation fracture pressure gradient of a pre-exploration well shown in an embodiment of the present invention;

[0079] Fig. 9 A data diagram of a drilling fluid target density of a pre-exploration well shown in an embodiment of the present invention;

[0080] Fig.10 The figure is a schematic diagram of the hardware structure of a control system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0081] The technical solution in the embodiment of the present invention will be described below in conjunction with the accompanying drawings in the embodiment of the present invention. Among them, in the description of the present invention, unless otherwise specified, " / " indicates that the objects associated before and after are in an "or" relationship, for example, A / B can represent A or B; the "or" in the present invention is only a description of the association relationship of associated objects, indicating that there can be three relationships, for example, A or B can represent: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. And, in the description of the present invention, unless otherwise specified, "multiple" means two or more than two. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items.

[0082] In addition, in order to clearly describe the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, the words "first", "second", etc. are used to distinguish the same items or similar items with substantially the same functions and effects. Those skilled in the art can understand that the words "first", "second", etc. do not limit the quantity and execution order, and the words "first", "second", etc. do not necessarily limit the difference.

[0083] Meanwhile, in the embodiments of the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way for easy understanding.

[0084] During the drilling process, the density of the drilling fluid needs to be controlled to ensure the balance of the bottom hole pressure and prevent well kicks and well leakage accidents during the drilling process. Pre-exploration wells are a type of drilling carried out for the purpose of confirming the location and properties of underground oil and gas. Due to the small number of wells drilled in the block where the pre-exploration well is located and the scarcity of reference data from adjacent wells, the uncertainty of the wellbore pressure profile of the pre-exploration well is large, and the wellbore pressure control and drilling fluid density control during the drilling process are difficult, which is prone to well control and well leakage risks, bringing huge challenges to the safe drilling of pre-exploration wells.

[0085] For pre-exploration wells, related technologies usually rely on seismic data to predict formation pore pressure and formation fracture pressure profiles to establish a wellbore drilling fluid density window. However, this method is limited by the accuracy of seismic data, resulting in large errors in the predicted drilling fluid density window, and the density window cannot be updated in real time during the drilling process. The drilling fluid density can only be regulated based on the drilling site experience. The lack of scientific data support leads to frequent well leakage and well kick accidents during the drilling process, which lengthens the drilling cycle and increases the drilling cost. CN116244938A proposes a method for optimizing the design of drilling fluid density in mud shale formations. The specific process includes obtaining the physical property parameters of mud shale cores; establishing a mechanical model of wellbore instability containing a weak surface structure according to the wellbore instability mechanism; judging the collapse of the rock around the well according to the Mohr-Coulomb failure criterion and the weak surface failure criterion, and determining the minimum drilling fluid density and the maximum drilling fluid density for maintaining the wellbore stability of the mud shale formation in combination with the allowable collapse degree of the project; fitting the relationship between the mechanical drilling speed and the static liquid column pressure of the mud shale formation at different depths, and calculating the upper limit of the drilling fluid density at the critical mechanical drilling speed; and obtaining the design range of the drilling fluid density window for the mud shale formation considering the wellbore stability and rapid drilling according to the minimum drilling fluid density, the maximum drilling fluid density and the upper limit of the drilling fluid density at the critical mechanical drilling speed. The above method is used to obtain the lower limit of drilling fluid density that meets the allowable collapse degree of the project and the upper limit of drilling fluid density for the optimal mechanical drilling speed. The lower limit of drilling fluid density that meets the allowable collapse degree of the project and the optimal mechanical drilling speed are determined by considering the maximum allowable wellbore collapse degree and the maximum mechanical drilling speed. However, this method still belongs to static design analysis and cannot update the drilling fluid density window and adjust the drilling fluid density according to the actual drilling information during the actual drilling process. CN109509111A proposes to calculate the rock density curve that has not been tested by shallow logging and splice it with the density curve obtained by logging to obtain the density curve from the surface to the deep reservoir section; calculate the overlying formation pressure and hydrostatic pressure based on the density curve; calculate the formation pressure of the shallow clastic rock formation; calculate the formation pressure of the gas-bearing shale reservoir; calculate the formation pressure of the carbonate reservoir; in the above steps, different pressure prediction models are used for different lithologies to improve the formation pressure prediction accuracy. However, this method still predicts formation pressure based on logging data of adjacent wells before drilling, and is not suitable for the situation where there is a lack of logging data of adjacent wells in the pre-exploration well. At the same time, the drilling fluid density cannot be updated and adjusted based on the actual drilling information during the drilling process.

[0086] Therefore, a method and system for regulating the density of drilling fluid in a pre-exploration well while drilling is urgently needed to realize real-time updating of the safe drilling fluid density window of the pre-exploration well during the drilling process, and then realize precise regulation of the drilling fluid density, thereby reducing the complex risks of well leakage and well kick accidents.

[0087] In view of this, an embodiment of the present invention provides a method for controlling the density of drilling fluid in a pre-exploration well while drilling, the method comprising: obtaining drilling parameter data of a drilled section, the parameter data including mechanical drilling speed, drill bit speed, drilling pressure, drill bit diameter, formation water density and actual drilling fluid density corresponding to different well depths; determining a modified Dc index corresponding to different well depths according to the drilling parameter data of the drilled section; determining the vertical stress gradient of the pre-exploration well according to the modified Dc index corresponding to different well depths, wherein the drilling of the drilled section is located in the pre-exploration well; determining the vertical stress gradient of the pre-exploration well according to the modified Dc index corresponding to the different well depths ... The vertical stress gradient of the well determines the formation pore pressure gradient and formation fracture pressure gradient of the pre-exploration well; the rock drilling resistance of the pre-exploration well is determined according to the drilling parameter data of the drilled section; the drilling fluid density safety margin weight of the pre-exploration well at the first well depth is determined according to the modified Dc index and rock drilling resistance of the pre-exploration well; the drilling fluid target density of the pre-exploration well is determined according to the formation pore pressure gradient, formation fracture pressure gradient and drilling fluid density safety margin weight of the pre-exploration well at the first well depth; the drilling fluid density of the pre-exploration well is adjusted to the drilling fluid target density.

[0088] The method provided by the present invention can determine the safe drilling fluid density window of the pre-exploration well and the drilling fluid density corresponding to the pre-exploration well at different well depths by acquiring the drilling parameter data of the drilled section, thereby realizing accurate control of the drilling fluid density, thereby reducing the complicated risks of well leakage and well kick accidents. In other words, the method provided by the present invention aims at the problems of little drilling data for the pre-exploration well, low accuracy in establishing the safe density window through seismic data, and high risk of well kick and well leakage due to the use of inappropriate drilling fluid density during the drilling process. A method for determining the safe density window while drilling and controlling the drilling fluid density that does not rely on logging and seismic data is proposed, which improves the ability to control the wellbore pressure during the drilling of the pre-exploration well, and provides an effective technical solution for reducing the risk of well leakage and well kick during the drilling of the pre-exploration well.

[0089] In some embodiments, the method for controlling the density of drilling fluid in a pre-exploration well while drilling provided by the embodiments of the present invention can be performed by a system 100 for controlling the density of drilling fluid in a pre-exploration well while drilling (hereinafter referred to as the control system 100). As an example, the control system 100 can be any electronic device 200 with data processing capabilities, such as a general-purpose computer, a personal computer, a laptop computer, a switch or a tablet computer, etc. The specific implementation of the purchase list control system 100 is not limited here.

[0090] Figure 1 The hardware structure diagram of the electronic device provided by the embodiment of the present invention is shown. The electronic device 200 includes a processor 210, a memory 220 and a communication interface 230.

[0091] The processor 210 may include one or more processing cores. The processor 210 uses various interfaces and lines to connect various parts in the electronic device 200, and executes various functions and processes data of the electronic device 200 by running or executing instructions, programs, code sets or instruction sets stored in the memory 220, and calling data stored in the memory 220. Optionally, the processor 210 can be implemented in at least one hardware form of a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processing (DSP), a field-programmable gate array (FPGA), and a programmable logic array (PLA).

[0092] The memory 220 may include a random access memory (RAl) or a read-only memory (ROL). Optionally, the memory 220 includes a non-transitory computer-readable storage medium (non-transitory colputer-readable storage lediul). The memory 220 may be used to store instructions, programs, codes, code sets or instruction sets. The memory 220 may include a program storage area. The program storage area may store instructions for implementing an operating system, instructions for implementing at least one function (such as a data acquisition function, a density control function, etc.), instructions for implementing the above-mentioned various method embodiments, etc.

[0093] The communication interface 230 is used to communicate with other devices, equipment or communication networks, such as data storage devices, image processing equipment or Ethernet, radio access network (RAN), wireless local area networks (WLAN), etc.

[0094] In physical implementation, the above-mentioned components (such as processor 210, memory 220 and communication interface 230) can be components in the same device (such as a laptop). Alternatively, at least two of the components can be set in the same device, that is, as different components in one device, such as a deployment method similar to devices or components in a distributed system.

[0095] It is to be understood that the structure illustrated in this embodiment does not constitute a specific limitation on the electronic device 200. In other embodiments of the present invention, the electronic device 200 may include more or fewer components than those illustrated, or combine certain components, or separate certain components, or arrange the components differently. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.

[0096] The following describes the method for controlling the density of drilling fluid in a pre-exploration well while drilling provided by an embodiment of the present invention in conjunction with the accompanying drawings.

[0097] Figure 2 The flowchart of a method for controlling the density of drilling fluid in a prospecting well while drilling is provided in an embodiment of the present invention. Optionally, the method may be Figure 1 The electronic device 200 shown is executed, that is, executed by the control system 100. The method may include the following steps:

[0098] S1. Obtain drilling parameter data of the drilled section.

[0099] The parameter data include mechanical drilling speed, drill bit speed, drilling pressure, drill bit diameter, formation water density and actual drilling fluid density corresponding to different well depths.

[0100] S2. Determine the modified Dc index corresponding to different well depths according to the drilling parameter data of the drilled section.

[0101] Specifically, the modified Dc index is the Dc index, which is an index for calculating pressure by correcting the drilling fluid density or the formation pressure index. During the drilling process, the Dc index is used to reflect the relationship between the ratio of the drilling fluid density to the actual drilling fluid density and the Dc index.

[0102] In a possible implementation, the formula for determining the modified Dc index Dc is:

[0103]

[0104] Among them, ROP is the mechanical drilling speed, in m / h; RPM is the drill bit speed, in r / min; WOB is the drilling pressure, in kN; d b is the drill bit diameter, in mm; ρ w is the formation water density, in g / cm 3 ; The value is 1.05g / cm 3 ρ 钻井液 The actual drilling fluid density of the drilled section, in g / cm 3 .

[0105] For example, see Figure 3 , Figure 3This is a data diagram of a modified Dc index of a pre-exploration well shown in an embodiment of the present invention. Different modified Dc indexes (Dc indexes) correspond to well depths from 0 meters to 3600 meters.

[0106] S3. Determine the vertical stress gradient of the exploration well according to the modified Dc index corresponding to different well depths.

[0107] Among them, the drilling of the drilled section is located in the pre-exploration well.

[0108] In some embodiments, see Figure 4 The above S3 specifically includes the following steps:

[0109] S31. Determine the formation porosity according to the modified Dc index corresponding to different well depths.

[0110] Specifically, the formula for determining the formation porosity φ is the first formula or the second formula, and the first formula is:

[0111] φ=aexp (b×Dc) ;

[0112] a and b are model coefficients;

[0113] The second formula is:

[0114]

[0115] Among them, A, B, λ and k are model coefficients, and md is the well depth in meters.

[0116] S32. Determine the rock density of the formation based on the porosity of the formation.

[0117] Specifically, the formula for determining the formation rock density ρ is:

[0118] ρ=ρ matrix (1-φ)+ρ w φ;

[0119] ρ matrix is the rock skeleton density, in g / cm 3 .

[0120] For example, see Figure 5 , Figure 5 A data diagram of formation rock density of a pilot well shown in an embodiment of the present invention.

[0121] S33. Determine the vertical stress gradient of the pilot well according to the formation rock density.

[0122] Specifically, the vertical stress gradient ρ v The formula for determining is:

[0123]

[0124] ρ v =σ v ×0.00981 / TVD;

[0125] σ v is the vertical stress, in MPa; g is the gravitational acceleration, in m / s 2 ; ρ is the rock density of the calculated well section dTVD formation, in g / cm 3 ; TVD1 is the starting vertical depth, the unit is m, and the value is 0; TVD2 is the ending vertical depth, the unit is m, and TVD is the vertical depth of the calculation point, the unit is m.

[0126] Exemplary, combined Figure 5 , see Figure 6 , Figure 6 Based on Figure 5 The formation rock density profile shown is a data diagram of the vertical stress gradient of the formation in the exploration well obtained by integrating the formation rock density at a depth of 0-3600m.

[0127] S4. Determine the formation pore pressure gradient and formation fracture pressure gradient of the exploration well according to the vertical stress gradient of the exploration well.

[0128] In some embodiments, the above S4 includes:

[0129] Determine the formation pore pressure corresponding to different well depths of the pre-exploration well according to the vertical stress gradient of the pre-exploration well; determine the formation pore pressure gradient of the pre-exploration well according to the formation pore pressure and vertical stress gradient corresponding to different well depths of the pre-exploration well; determine the formation fracture pressure gradient of the pre-exploration well according to the formation pore pressure gradient of the pre-exploration well;

[0130] Specifically, the formula for determining the formation pore pressure is:

[0131] σ e =σ vA -P pA =σ vB -P pB ;

[0132] P pB =P pA -(σ vA -σ vB );

[0133] Among them, σ e Effective overburden pressure, in MPa; σ vA The vertical stress at the well depth A is in MPa; P pA The formation pore pressure at the well depth A, in MPa; σ vBThe vertical stress at the well depth B is in MPa; P pB The formation pore pressure at the well depth B, in MPa;

[0134] The control system 100 determines the normal formation pore pressure at the well depth A according to the drilling parameter data of the drilled section, and then obtains the formation pore pressure P at the well depth B according to the vertical stress at the well depths A and B in the vertical stress gradient. pB , and then the formation pore pressure corresponding to the exploration well at different depths can be obtained, thereby obtaining the formation pore pressure gradient ρ of the exploration well p .

[0135] Furthermore, the formation pore pressure gradient ρ of the pilot well p The formula for determining is:

[0136] ρ p =P p / (0.00981×TVD);

[0137] Among them, P p is the formation pore pressure, in MPa;

[0138] For example, see Figure 7 , Figure 7 This is a data diagram of the formation pore pressure gradient of a pre-exploration well shown in an embodiment of the present invention.

[0139] In a possible implementation, the formation fracture pressure gradient ρ of the pilot well is f The determination formula is the third formula or the fourth formula;

[0140] The third formula is:

[0141]

[0142] Wherein, μ is the Poisson’s ratio of the formation rock, dimensionless;

[0143] The fourth formula is:

[0144] ρ f =k1+k2(P p -P n ) / (TVD*0.00981);

[0145] P n =1.05×0.00981×TVD;

[0146] k1 and k2 are model coefficients; P n The pore pressure of the formation under normal compaction conditions, in MPa.

[0147] It should be understood that the model coefficients k1 and k2 can be flexibly set according to the actual usage scenario, and the embodiment of the present invention does not impose any particular limitation on the specific values ​​of the model coefficients k1 and k2.

[0148] For example, see Figure 8 , Figure 8 This is a data diagram of the formation fracture pressure gradient of a pre-exploration well shown in an embodiment of the present invention.

[0149] S5. Determine the rock drilling resistance of the pre-exploration well based on the drilling parameter data of the drilled section.

[0150] Specifically, the formula for determining the rock drilling resistance S of the pilot well is:

[0151] S=2×WOB / (d b ×ROP / RPM).

[0152] Among them, RPM is the drill speed.

[0153] S6. Determine the drilling fluid density safety margin weight of the exploration well at the first well depth according to the modified Dc index of the exploration well and the rock drilling resistance strength.

[0154] In a possible implementation, the formula for determining the safety margin weight of the drilling fluid density of the pre-exploration well at the first well depth is:

[0155]

[0156]

[0157] Where w is the safety margin weight of drilling fluid density; S n+1 is the rock drilling resistance of the exploration well at the first depth, S n Dc is the rock drilling resistance of the exploration well at the second well depth; n+1 is the modified Dc index of the pilot well at the first depth, Dc n is the modified Dc index of the exploration well at the second well depth, w n+1 is the safety margin weight of drilling fluid density at the first well depth of the pre-exploration well; w n is the safety margin weight of the drilling fluid density of the pre-exploration well at the second well depth; the first well depth is greater than the second well depth; ζ1, ζ2, ζ3 are model coefficients.

[0158] It should be noted that when the depth of the pre-exploration well increases from the second depth to the first depth, when the rock drilling resistance increases, it means that the formation fracture pressure increases, and vice versa; when the modified Dc index increases, the formation pore pressure increases, and vice versa.

[0159] Specifically, the weight of the drilling fluid density safety margin of the pre-exploration well at the first well depth is determined according to the modified Dc index and the rock drill resistance. When the well depth of the pre-exploration well increases from the second well depth to the first well depth, when the modified Dc index and the rock drill resistance increase at the same time, the risk of formation overflow increases, and the weight of the drilling fluid density safety margin also needs to be increased accordingly; when the rock drill resistance increases and the modified Dc index decreases, the pressure system is relatively safe, and the weight of the drilling fluid density safety margin remains unchanged; when the rock drill resistance decreases and the modified Dc index increases, the risk of formation overflow and leakage increases, and the weight of the drilling fluid density safety margin increases; when the rock drill resistance decreases and the modified Dc index decreases, the risk of formation leakage increases, and the weight of the drilling fluid density safety margin decreases.

[0160] In one example, the drilling fluid density safety margin weight w of the pilot well at the second well depth is n is 0.5. It should be noted that technicians can adjust the drilling fluid density safety margin weight w of the pre-exploration well at the second well depth according to the actual scenario. n The above is only an example and is not particularly limited.

[0161] In another example, the first well depth is 2910 meters, and the formation pore pressure gradient at the well depth of 2910m is 1.05g / cm 3 , rupture pressure gradient 1.79g / cm 3 At this time, the rock drilling resistance is 358.6MPa, the mechanical drilling speed is 8.5m / hr, and the Dc index is 18.4. The second well depth is 2900 meters. At 2900m, the rock drilling resistance is 89MPa, the mechanical drilling speed is 19.5m / hr, and the Dc index is 4. n is 0.2, obviously the rock drilling resistance and Dc index both increase.

[0162] w n+1 =w n +ζ1w n =0.888.

[0163] S7. Determine the target density of the drilling fluid of the exploration well according to the formation pore pressure gradient, formation fracture pressure gradient, and drilling fluid density safety margin weight of the exploration well at the first well depth.

[0164] In some embodiments, the above S7 includes:

[0165] Determine the drilling fluid safety density window of the pre-exploration well according to the formation pore pressure gradient, formation fracture pressure gradient and drilling fluid density safety margin weight of the pre-exploration well; determine the drilling fluid target density of the pre-exploration well according to the drilling fluid safety density window and drilling fluid density safety margin weight of the pre-exploration well;

[0166] The formula for determining the drilling fluid safety density window △ρ is:

[0167] Δρ=ρ f -ρ p =(1-w)Δρ 上 +wΔρ 下 =(1-w)ρ f -wρ p +(2w-1)ρ 钻井液 ;

[0168] Δρ 上 =ρ f -ρ 钻井液 ;

[0169] Δρ 下 =ρ 钻井液 -ρ p ;

[0170] Among them, △ρ 上 is the upper boundary safety margin; △ρ 下 is the lower boundary safety margin.

[0171] From the above, it can be seen that the method provided in the embodiment of the present invention determines the drilling fluid safety density window of the pre-exploration well according to the formation pore pressure gradient, formation fracture pressure gradient and drilling fluid density safety margin weight of the pre-exploration well, and can realize safety monitoring of the pre-exploration well according to the drilling fluid safety density window to avoid safety accidents.

[0172] Drilling fluid target density ρ 目标密度 The formula for determining is:

[0173]

[0174] For example, see Fig. 9 , Fig. 9 This is a data graph of drilling fluid target density of a pilot well shown in an embodiment of the present invention. It includes formation pore pressure gradient, formation fracture pressure gradient and drilling fluid target density corresponding to different well depths of the pilot well. Among them, the data line on the left is the formation pore pressure corresponding to different well depths, the data line in the middle is the drilling fluid target density corresponding to different well depths, and the data line on the right is the formation fracture pressure corresponding to different well depths.

[0175] S8. Adjust the drilling fluid density of the pilot well to the target drilling fluid density.

[0176] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in combination with a specific example, taking the exploration well A as the exploration well as an example.

[0177] As can be seen from S1-S8 above, the method provided by the embodiment of the present invention can determine the safe drilling fluid density window of the pre-exploration well and the drilling fluid density corresponding to the pre-exploration well at different well depths by acquiring the drilling parameter data of the drilled section, thereby realizing accurate control of the drilling fluid density, thereby reducing the complicated risks of well leakage and well kick accidents. In other words, the method provided by the present invention aims at the problems of little drilling data for the pre-exploration well, low accuracy in establishing the safe density window through seismic data, and high risk of well kick and well leakage due to the use of inappropriate drilling fluid density during the drilling process. A method for determining the safe density window while drilling and controlling the drilling fluid density that does not rely on logging and seismic data is proposed, which improves the ability to control the wellbore pressure during the drilling of the pre-exploration well, and provides an effective technical solution for reducing the risk of well leakage and well kick during the drilling of the pre-exploration well.

[0178] The above mainly introduces the scheme of the embodiment of the present invention from the perspective of the method. It can be understood that in order to realize the above functions, the control system 100 includes at least one of the hardware structure and software modules corresponding to each function. It should be easy for those skilled in the art to realize that, in combination with the units and algorithm steps of each example described in the embodiment disclosed in this article, the embodiment of the present invention can be implemented in the form of hardware or a combination of hardware and computer software. Whether a function is executed in the form of hardware or computer software driving hardware depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the embodiment of the present invention.

[0179] The embodiment of the present invention can divide the control system 100 into functional units according to the above method example. For example, the control system 100 can be divided into functional units corresponding to various functions, or two or more functions can be integrated into one processing unit. The above integrated unit can be implemented in the form of hardware or in the form of software functional units. It should be noted that the division of units in the embodiment of the present invention is schematic and is only a logical functional division. There may be other division methods in actual implementation.

[0180] For example, Fig.10The hardware structure diagram of a control system provided by an embodiment of the present invention is shown. The control system 100 includes: a data acquisition module 110, which is used to acquire drilling parameter data of the drilled section, and the parameter data includes mechanical drilling speed, drill bit speed, drilling pressure, drill bit diameter, formation water density and actual drilling fluid density corresponding to different well depths; an index determination module 120, which is used to determine the modified Dc index corresponding to different well depths according to the drilling parameter data of the drilled section; a stress determination module 130, which is used to determine the vertical stress gradient of the pre-exploration well according to the modified Dc index corresponding to different well depths, wherein the drilling of the drilled section is located in the pre-exploration well; a pressure determination module 140, which is used to determine the vertical stress gradient of the pre-exploration well according to the vertical stress gradient of the pre-exploration well The invention relates to a drilling fluid control module 180, which is used to determine the drilling fluid target density of the pre-exploration well according to the formation pore pressure gradient and formation fracture pressure gradient of the pre-exploration well; a strength determination module 150, which is used to determine the rock drilling resistance of the pre-exploration well according to the drilling parameter data of the drilled section; a weight determination module 160, which is used to determine the drilling fluid density safety margin weight of the pre-exploration well at the first well depth according to the modified Dc index and the rock drilling resistance of the pre-exploration well; a density determination module 170, which is used to determine the drilling fluid target density of the pre-exploration well according to the formation pore pressure gradient, the formation fracture pressure gradient and the drilling fluid density safety margin weight of the pre-exploration well at the first well depth; and a density control module 180, which is used to adjust the drilling fluid density of the pre-exploration well to the drilling fluid target density.

[0181] The formula for determining the safety margin weight of the drilling fluid density of the pilot well at the first well depth is:

[0182]

[0183] Where w is the safety margin weight of drilling fluid density; S n+1 is the rock drilling resistance of the exploration well at the first depth, S n Dc is the rock drilling resistance of the exploration well at the second well depth; n+1 is the modified Dc index of the pilot well at the first depth, Dc n is the modified Dc index of the exploration well at the second well depth, w n+1 is the safety margin weight of drilling fluid density at the first well depth of the pre-exploration well; w n is the safety margin weight of the drilling fluid density of the pre-exploration well at the second well depth; the first well depth is greater than the second well depth; ζ1, ζ2, ζ3 are model coefficients.

[0184] It should be understood that the specific description of the above optional methods can refer to the above method embodiments, which will not be repeated here. In addition, the explanation of any of the control systems 100 provided above and the description of the beneficial effects can refer to the above corresponding method embodiments, which will not be repeated here.

[0185] The embodiment of the present invention further provides a computer-readable storage medium, in which at least one computer instruction is stored, and the at least one computer instruction is loaded and executed by a processor to implement the methods of the above embodiments. For the explanation of the relevant contents and the description of the beneficial effects in any of the above-mentioned computer-readable storage media, reference can be made to the above-mentioned corresponding embodiments, which will not be repeated here.

[0186] The embodiment of the present invention further provides a chip. The chip integrates a control circuit and one or more ports for realizing the functions of the above-mentioned control system 100. Optionally, the functions supported by the chip can be referred to above and will not be described in detail here.

[0187] Those skilled in the art will appreciate that all or part of the steps of the above embodiments can be implemented by instructing the relevant hardware through a program, and the program can be stored in a computer-readable storage medium. The above-mentioned storage medium can be a read-only memory, a random access memory, etc. The above-mentioned processing unit or processor can be a central processing unit, a general-purpose processor, a specific circuit structure (application specific integrated circuit, ASIC), a microprocessor (digital signal processor, DSP), a field programmable gate array (field programmable gate array, FPGA) or other programmable logic devices, transistor logic devices, hardware components or any combination thereof.

[0188] The embodiment of the present invention also provides a computer program product including instructions, when the instructions are run on a computer, the computer executes any one of the methods in the above embodiments. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on the computer, the process or function according to the embodiment of the present invention is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network or other programmable device. The computer instructions may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from one website, computer, server or data center to another website, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium may be any available medium that can be accessed by a computer or a data storage device such as a server or data center that includes one or more available media integrated therein. The available medium may be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., an SSD), etc.

[0189] It should be noted that the above-mentioned devices for storing computer instructions or computer programs provided in the embodiments of the present invention, such as but not limited to the above-mentioned memory, computer-readable storage medium and communication chip, etc., all have non-transitory. Those skilled in the art should be aware that in one or more of the above-mentioned examples, the functions described in the embodiments of the present invention can be implemented with hardware, software, firmware or any combination thereof. When implemented using software, these functions can be stored in a computer-readable storage medium or transmitted as one or more instructions or codes on a computer-readable storage medium. Computer-readable storage media include computer storage media and communication media, wherein the communication medium includes any medium that is convenient for transmitting a computer program from one place to another. The storage medium can be any available medium that a general or special-purpose computer can access.

[0190] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for controlling the density of drilling fluid in a pre-exploration well while drilling, characterized in that: The method comprises: Acquire drilling parameter data of the drilled section, wherein the parameter data includes mechanical drilling speed, drill bit speed, drilling pressure, drill bit diameter, formation water density and actual drilling fluid density corresponding to different well depths; Determining the modified Dc index corresponding to different well depths according to the drilling parameter data of the drilled section; Determining the vertical stress gradient of the pre-exploration well according to the modified Dc index corresponding to different well depths, wherein the well of the drilled section is located in the pre-exploration well; Determine the formation pore pressure gradient and formation fracture pressure gradient of the pre-exploration well according to the vertical stress gradient of the pre-exploration well; Determining the rock drilling resistance of the pre-exploration well according to the drilling parameter data of the drilled section; Determine the drilling fluid density safety margin weight of the pre-exploration well at the first well depth according to the modified Dc index of the pre-exploration well and the rock drilling resistance strength; Determine the drilling fluid target density of the pre-exploration well according to the formation pore pressure gradient, formation fracture pressure gradient, and drilling fluid density safety margin weight of the pre-exploration well at the first well depth; Adjusting the drilling fluid density of the pilot well to the drilling fluid target density; The formula for determining the safety margin weight of the drilling fluid density of the pilot well at the first well depth is: Where w is the safety margin weight of drilling fluid density; S n+1 is the rock drilling resistance strength of the pilot well at the first well depth, S n Dc is the rock drilling resistance of the pilot well at the second well depth; n+1 is the modified Dc index of the pilot well at the first well depth, Dc n is the modified Dc index of the pilot well at the second well depth, w n+1 w is the safety margin weight of the drilling fluid density of the pilot well at the first well depth; n is the safety margin weight of the drilling fluid density of the pre-exploration well at the second well depth; the first well depth is greater than the second well depth; ζ1, ζ2, ζ3 are model coefficients.

2. The method according to claim 1, characterized in that The formula for determining the modified Dc index is: Among them, ROP is the mechanical drilling speed, in m / h; RPM is the drill bit speed, in r / min; WOB is the drilling pressure, in kN; d b is the drill bit diameter, in mm; ρ w is the formation water density, in g / cm 3 , the value is 1.05g / cm 3 ρ 钻井液 is the actual drilling fluid density of the drilled section, in g / cm 3 .

3. The method according to claim 2, characterized in that The method of determining the vertical stress gradient of the prospecting well according to the modified Dc index corresponding to different well depths includes: Determine the formation porosity based on the modified Dc index corresponding to different well depths; Determine the density of formation rocks based on formation porosity; Determine the vertical stress gradient of the pilot well according to the rock density of the formation; The formula for determining the formation porosity φ is the first formula or the second formula. The first formula is: φ=aexp (b×Dc) ; a and b are model coefficients; The second formula is: Among them, A, B, λ and k are model coefficients, and md is the well depth in meters.

4. The method according to claim 3, characterized in that The formula for determining the formation rock density ρ is: p=p matrix (1-φ)+ρ w f; ρ matrix is the rock skeleton density, in g / cm 3 ; Vertical stress gradient ρ v The formula for determining is: r v =s v ×0.00981 / TVD; σ v is the vertical stress, in MPa; g is the gravitational acceleration, in m / s 2 ; ρ is the rock density of the calculated well section dTVD formation, in g / cm 3 ; TVD1 is the starting vertical depth, the unit is m, and the value is 0; TVD2 is the ending vertical depth, the unit is m, and TVD is the vertical depth of the calculation point, the unit is m.

5. The method according to claim 4, characterized in that The step of determining the formation pore pressure gradient and the formation fracture pressure gradient of the pre-exploration well according to the vertical stress gradient of the pre-exploration well comprises: Determining the formation pore pressure corresponding to different well depths of the pre-exploration well according to the vertical stress gradient of the pre-exploration well; Determining the formation pore pressure gradient of the pre-exploration well according to the formation pore pressure and vertical stress gradient corresponding to different well depths of the pre-exploration well; Determining the formation fracture pressure gradient of the pre-exploration well according to the formation pore pressure gradient of the pre-exploration well; The formula for determining formation pore pressure is: s e =s vA -P pA =s vB -P pB ; P pB =P pA -(s vA -s vB ); Among them, σ e Effective overburden pressure, in MPa; σ vA The vertical stress at the well depth A is in MPa; P pA The formation pore pressure at the well depth A, in MPa; σ vB The vertical stress at the well depth B is in MPa; P pB The formation pore pressure at the well depth B, in MPa; Formation pore pressure gradient ρ of the pilot well p The formula for determining is: r p =P p / (0.00981×TVD); Among them, P p is the formation pore pressure, in MPa; Formation fracture pressure gradient ρ of the pilot well f The determination formula is the third formula or the fourth formula; The third formula is: Wherein, μ is the Poisson’s ratio of the formation rock, dimensionless; The fourth formula is: r f =k1+k2(P p -P n ) / (TVD*0.00981); P n =1.05×0.00981×TVD; k1 and k2 are model coefficients; P n The pore pressure of the formation under normal compaction conditions, in MPa.

6. The method according to claim 5, characterized in that The formula for determining the rock drilling resistance S of the pilot well is: S=2×WOB / (d b ×ROP / RPM); Among them, RPM is the drill speed.

7. The method according to claim 6, characterized in that Determining the drilling fluid target density of the pre-exploration well according to the formation pore pressure gradient, formation fracture pressure gradient, and drilling fluid density safety margin weight of the pre-exploration well at the first well depth includes: Determine the drilling fluid safety density window of the pre-exploration well according to the formation pore pressure gradient, formation fracture pressure gradient and drilling fluid density safety margin weight of the pre-exploration well; Determining the drilling fluid target density of the pre-exploration well according to the drilling fluid safety density window and the drilling fluid density safety margin weight of the pre-exploration well; The formula for determining the drilling fluid safety density window △ρ is: Dr=r f -r p =(1-w)Dr 上 +wDr 下 =(1-w)ρ f -wρ p +(2w-1)ρ 钻井液 ; Dr. 上 =ρ f -r 钻井液 ; Dr. 下 =ρ 钻井液 -r p ; Among them, △ρ 上 is the upper boundary safety margin; △ρ 下 is the lower boundary safety margin.

8. The method according to claim 7, characterized in that Drilling fluid target density ρ 目标密度 The formula for determining is:

9. A drilling fluid density control system for a pre-exploration well, characterized in that: The system comprises: A data acquisition module is used to acquire drilling parameter data of the drilled section, wherein the parameter data includes mechanical drilling speed, drill bit speed, drilling pressure, drill bit diameter, formation water density and actual drilling fluid density corresponding to different well depths; An index determination module, used to determine the modified Dc index corresponding to different well depths according to the drilling parameter data of the drilled section; A stress determination module, used to determine the vertical stress gradient of the pre-exploration well according to the modified Dc index corresponding to different well depths, wherein the well of the drilled section is located in the pre-exploration well; A pressure determination module, used to determine the formation pore pressure gradient and formation fracture pressure gradient of the pre-exploration well according to the vertical stress gradient of the pre-exploration well; A strength determination module, used to determine the rock drilling resistance strength of the pre-exploration well according to the drilling parameter data of the drilled section; A weight determination module, used to determine the drilling fluid density safety margin weight of the pre-exploration well at the first well depth according to the modified Dc index of the pre-exploration well and the rock drilling resistance strength; A density determination module, used to determine the target density of the drilling fluid of the pre-exploration well according to the formation pore pressure gradient, the formation fracture pressure gradient, and the drilling fluid density safety margin weight of the pre-exploration well at the first well depth; A density control module, used for adjusting the drilling fluid density of the pilot well to the drilling fluid target density; The formula for determining the safety margin weight of the drilling fluid density of the pilot well at the first well depth is: Where w is the safety margin weight of drilling fluid density; S n+1 is the rock drilling resistance strength of the pilot well at the first well depth, S n Dc is the rock drilling resistance of the pilot well at the second well depth; n+1 is the modified Dc index of the pilot well at the first well depth, Dc n is the modified Dc index of the pilot well at the second well depth, w n+1 w is the safety margin weight of the drilling fluid density of the pilot well at the first well depth; n is the safety margin weight of the drilling fluid density of the pre-exploration well at the second well depth; the first well depth is greater than the second well depth; ζ1, ζ2, ζ3 are model coefficients.

10. An electronic device, characterized in that: include: processor; a memory for storing instructions executable by the processor; The processor is configured to execute the instructions to implement the method for controlling the density of drilling fluid while drilling in a prospecting well as described in any one of claims 1 to 8.

Images