A method for designing wellbore structure in deep wells with complex formations based on multi-objective optimization

Abstract

The present invention discloses a method for designing a wellbore structure in a deep well with complex formations based on multi-objective optimization, including: step one, quantitative description of formation pressure uncertainty of the well to be analyzed; step two, establishment of a safe drilling fluid density window for the well to be analyzed; step three, quantitative risk assessment for a specific wellbore structure scheme for the well to be analyzed; if the result of the quantitative risk assessment is less than the preset risk value, a specific wellbore structure scheme is selected; if the result of the quantitative risk assessment is greater than or equal to the preset risk value, the wellbore structure scheme is readjusted. In this scheme, a casing layer and down-depth potential risk assessment method based on reliability theory is established to conduct risk assessment on wellbore structures of different schemes, so as to select the scheme with the least risk; at the same time, the probability of risk occurrence can be reduced by optimizing the construction parameters, so as to maximize the drilling safety in the design stage.

Description

Technical Field

[0001] The invention relates to the technical field of deep well complex formation drilling, and in particular to a deep well complex formation wellbore structure design method based on multi-objective optimization. Background Art

[0002] Wellbore structure design is an important prerequisite for ensuring safe and efficient drilling. A reasonable wellbore structure scheme can effectively avoid drilling risks that may occur during drilling operations, such as well kick, well leakage, well wall collapse, and stuck drill. Wellbore structure design plays a connecting role in drilling engineering. Domestic and foreign petroleum researchers have conducted many years of exploration in this field and have achieved some research results. Looking at the historical trajectory of its development process, it can be roughly divided into three stages: experience accumulation stage, theoretical development stage, and system engineering stage. At present, the wellbore structure design methods at home and abroad are developing in the direction of system engineering. The basic idea is to form a system for all aspects of wellbore structure design, and then, based on the principles and methods of system engineering, the pressure balance relationship (formation pore pressure, formation fracture pressure, etc.), engineering constraints (collapsed well section, lost well section and stuck drill section), accident probability and other related factors, adopt risk decision-making technology to carry out reasonable wellbore structure design.

[0003] Conventional wellbore structure design is a system-wide local optimization method, while the wellbore structure design method for solving complex geological conditions is a system-wide comprehensive optimization method, which is a completely new concept in terms of both quality and quantity.

[0004] In particular, the particularity of deep drilling and the complexity and uncertainty of geological conditions are one of the main reasons for the frequent occurrence of complex underground situations during the drilling process, which also affects the design of the wellbore structure. Summary of the invention

[0005] In view of this, the present invention provides a method for designing a wellbore structure in deep wells with complex formations based on multi-objective optimization, which can reduce the probability of risk occurrence and maximize drilling safety during the design stage.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for designing a wellbore structure in a deep well with complex formations based on multi-objective optimization, comprising:

[0008] Step 1: Quantitative description of the uncertainty of formation pressure of the well to be analyzed;

[0009] Step 2: Establishment of safe drilling fluid density window for the well to be analyzed;

[0010] Step 3: Conduct a quantitative risk assessment on a specific wellbore structure scheme for the well to be analyzed; if the result of the quantitative risk assessment is less than the preset risk value, select a specific wellbore structure scheme; if the result of the quantitative risk assessment is greater than or equal to the preset risk value, redesign the wellbore structure scheme.

[0011] Preferably, in step 1, the uncertainty of the formation pressure of the well to be analyzed is quantitatively described, including:

[0012] Using Monte Carlo and uncertainty theory, we can obtain the formation pressure p of different types of wells to be analyzed. t Formation pressure profile with credibility;

[0013] A probability distribution model of formation pressure with depth in the well to be analyzed is established.

[0014] Preferably, the Monte Carlo and uncertainty theory are used to obtain the formation pressure p of different types of wells to be analyzed. t Credible formation pressure profiles, including:

[0015] The expression of the formation pressure curve with cumulative probability j0 is:

[0016]

[0017] In the formula, p t Represents different types of formation pressure, when t=p p Indicates the formation pore pressure, t = p cmin Indicates the minimum formation collapse pressure, t = p cmax Indicates the maximum formation collapse pressure, t = p f Indicates the formation fracture pressure;

[0018] According to probability statistics theory, the probability density function p of the formation pressure at each depth is t(h) [p t(h) ] and the cumulative probability distribution function F t(h) [p t(h) ]The analytical solution expression is as follows:

[0019]

[0020]

[0021] In the formula,

[0022] Preferably, in step 2, establishing the safe drilling fluid density window of the well to be analyzed includes:

[0023] According to the pressure constraint criterion, the upper and lower limits of safe drilling fluid density of the well to be analyzed are determined.

[0024] Preferably, the upper and lower limits of the safe drilling fluid density include: the lower limit value of the anti-kickback drilling fluid density ρ k(h) , Lower limit of drilling fluid density for preventing wellbore collapse ρ c1(h) , Upper limit value of drilling fluid density for preventing wellbore collapse ρ c2(h) , the upper limit value of drilling fluid density to prevent differential pressure sticking ρ sk(h) and the upper limit of the density of the anti-lost drilling fluid ρ L(h) ;

[0025] Determining the upper and lower limits of safe drilling fluid density of the well to be analyzed according to the pressure constraint criterion includes:

[0026] (1) Lower limit of drilling fluid density for preventing well kick ρ k(h) :

[0027] ρ k(h) =p t(h) +S b +Δρ,t=p p Indicates the formation pore pressure (4)

[0028] (2) Lower limit of drilling fluid density for preventing wellbore collapse ρ c1(h) and the upper limit of drilling fluid density ρ c2(h) :

[0029] ρ c1(h) =p t(h) +S b ,t=p cmin Indicates the minimum collapse pressure of the formation (5)

[0030] ρ c2(h) =p t(h) -S g ,t=p cmax Indicates the maximum collapse pressure of the formation (6)

[0031] (3) Upper limit of drilling fluid density ρ to prevent differential pressure sticking sk(h) :

[0032] t=p p Indicates the formation pore pressure (7)

[0033] (4) Upper limit of drilling fluid density for preventing leakage ρ L(h) :

[0034] ρ L(h) =p t(h) -S g -S f -S w -S c ,t=p f Indicates formation fracture pressure (8)

[0035] In the formula, S b is the pumping pressure coefficient, g / cm 3 ; S g is the excitation pressure coefficient, g / cm 3 ; Δρ is the additional drilling fluid density, g / cm 3 ; S f Increase the safety of formation fracture pressure, g / cm 3 ; S w Adding value to deepwater drilling fluid safety, g / cm 3 ; S c is the cycle pressure loss coefficient, g / cm 3 ; S k Well kick allowance, g / cm 3 ; ΔP is the allowable value of differential pressure for drilling, MPa; h pmax is the depth of the maximum formation pore pressure in the open hole section, m; h is the well depth, m.

[0036] Preferably, in step 3, a quantitative risk assessment is performed for a specific wellbore structure scheme of the well to be analyzed, including:

[0037] According to the upper and lower limits of safe drilling fluid density and its distribution state, the risk of well kick, well wall collapse, drilling leakage and differential pressure sticking at depth h are determined based on the reliability theory of generalized stress and strength interference:

[0038]

[0039]

[0040]

[0041] R L(h) =P(ρ d >ρ L(h) )=F ρL(h) (ρ d ) (12)

[0042] In the formula, R k(h) , R c(h) , R sk(h) , R L(h) They represent the risk of well kick, wellbore collapse, drilling leakage, and differential pressure sticking at depth h, respectively; ρ d is the density of drilling fluid during drilling, g / cm 3 .

[0043] Preferably, in step 3, after performing a risk quantitative assessment on a specific wellbore structure scheme of the well to be analyzed, the method further includes:

[0044] Step 4: Based on the risk assessment result of the wellbore structure scheme, if the risk assessment result is less than the risk preset value, a specific wellbore structure scheme is selected; if the risk quantitative assessment result is greater than or equal to the risk preset value, the construction parameters of the wellbore structure scheme are optimized.

[0045] Preferably, the construction parameters include: drilling fluid performance parameters, drilling fluid density parameters and / or drilling fluid drilling parameters.

[0046] Preferably, after step 4, the method further comprises:

[0047] Step 5: Based on the principle of lenient at the top and strict at the bottom and risk sharing, establish a wellbore structure design plan; the wellbore structure design plan includes:

[0048] (1) Establishment of the depth range below the surface casing;

[0049] (2) Establishment of the bandwidth of the first vertical strip;

[0050] (3) extension and folding of the belt;

[0051] (4) Establishment of casing layers and depth range.

[0052] Preferably, the (1) establishment of the depth range below the surface casing includes:

[0053] Based on the formation lithology data and the reference to the surface casing depth data of adjacent wells, the surface casing depth range is determined to be D 11 ~D 12 (D 11 <D 12 );Depth range B1=D 12 -D 11 Defined as the bandwidth of the first horizontal band, and called D 11 is the top edge of the horizontal strip, D 12 for the bottom edge;

[0054] The (2) establishment of the first vertical stripe bandwidth includes:

[0055] Extend the horizontal strip with bandwidth B1 horizontally, and the strips are respectively aligned with the curve and Intersecting at four points And M1 is defined as the bandwidth of the first vertical band:

[0056]

[0057] Similar to horizontal stripes, For this reason, the top edge of the vertical strip, for the bottom edge;

[0058] The (3) extension and folding of the belt comprises:

[0059] Similar to the establishment method of the first horizontal strip and the first vertical strip, the first vertical strip is extended downward to align with the curve The intersection produces the second horizontal strip, and so on, the strips extend and fold in a step-like manner until the final well depth; the calculation formula for the width of the vertical strips and horizontal strips during the extension and folding process is:

[0060]

[0061] Where, L -1 is the inverse function of L, n is the total number of casing layers;

[0062] The (4) establishment of casing layers and depth range includes:

[0063] The lower depth range of each layer of casing is the top and bottom edges of the corresponding horizontal strip.

[0064] It can be seen from the above technical solutions that the method for designing a wellbore structure in a deep well with complex formations based on multi-objective optimization provided by the present invention has the following beneficial effects:

[0065] 1. Taking into account the uncertainty of the geological environment of deep well drilling in complex formations, the formation pressure profile (or the upper and lower limits of the safe drilling fluid density window) used for wellbore structure design is no longer a single fixed value, but an interval with probability distribution characteristics; this processing method makes the formation pressure more consistent with the actual situation downhole, which is more conducive to wellbore structure design;

[0066] 2. A casing layer and depth potential risk assessment method based on reliability theory has been established, which can be used to conduct risk assessment on wellbore structures of different schemes, so as to select the scheme with the lowest risk. At the same time, the probability of risk can be reduced by optimizing the construction parameters, thus maximizing the drilling safety during the design stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] 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 some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0068] Figure 1 A flow chart of the wellbore structure design for deep wells with complex formations based on multi-objective optimization provided by an embodiment of the present invention;

[0069] Figure 2 A schematic diagram of a wellbore structure design method based on the principles of leniency above and strictness below and risk sharing provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0070] In order to overcome the defects of the background technology, the present invention discloses a method for designing a wellbore structure for complex formations in deep wells based on multi-objective optimization. Based on a quantitative description method for the complex geological environment with uncertainty in deep oil and gas drilling, a credible formation pressure profile of a deep well is constructed, and a reliability theory based on generalized stress and strength interference is used to quantitatively evaluate the potential engineering risks of the wellbore structure scheme; combined with the numerical simulation results of the drilling construction process under different wellbore structure schemes, the influence of each main construction parameter on the potential risk of a specific scheme is analyzed, and the mutual restriction relationship between the main construction parameters, casing layers and depth and other factors and the downhole engineering risks is determined; based on the principles of sharing the risks of each layer of casing, widening the top and tightening the bottom, and combining the adjustment of construction parameters with the adjustment of the wellbore structure, a wellbore structure design method based on multi-objective optimization suitable for complex formations in deep wells is established by using methods such as decision trees.

[0071] 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.

[0072] The method for designing a wellbore structure in a deep well with complex formations based on multi-objective optimization is provided in an embodiment of the present invention. Figure 1 As shown, including:

[0073] Step 1: Quantitative description of the uncertainty of formation pressure of the well to be analyzed;

[0074] Step 2: Establishment of safe drilling fluid density window for the well to be analyzed;

[0075] Step 3: Conduct a quantitative risk assessment on a specific wellbore structure scheme for the well to be analyzed; if the result of the quantitative risk assessment is less than the preset risk value, select a specific wellbore structure scheme; if the result of the quantitative risk assessment is greater than or equal to the preset risk value, redesign the wellbore structure scheme.

[0076] It can be seen from the above technical solutions that the method for designing a wellbore structure in a deep well with complex formations based on multi-objective optimization provided by the embodiment of the present invention has the following beneficial effects:

[0077] 1. Taking into account the uncertainty of the geological environment of deep well drilling in complex formations, the formation pressure profile (or the upper and lower limits of the safe drilling fluid density window) used for wellbore structure design is no longer a single fixed value, but an interval with probability distribution characteristics; this processing method makes the formation pressure more consistent with the actual situation downhole, which is more conducive to wellbore structure design;

[0078] 2. A casing layer and depth potential risk assessment method based on reliability theory has been established, which can be used to conduct risk assessment on wellbore structures of different schemes, so as to select the scheme with the lowest risk. At the same time, the probability of risk can be reduced by optimizing the construction parameters, thus maximizing the drilling safety during the design stage.

[0079] Furthermore, in step 1 of this scheme, the Monte Carlo and uncertainty theory are used to obtain the formation pressure p of different types of wells to be analyzed. t Credibility-based formation pressure profile; establish a probability distribution model of the formation pressure with depth in the well to be analyzed. Step 1 of this solution is designed in this way, taking into account the uncertainty of the geological environment of deep well drilling in complex formations, so that the formation pressure profile (or the upper and lower limits of the safe drilling fluid density window) used for wellbore structure design is no longer a single fixed value, but an interval with probability distribution characteristics; in this way, the formation pressure is more consistent with the actual situation downhole, which is more conducive to wellbore structure design. Figure 1 As shown, specifically:

[0080] Step 1: Quantitative description of formation pressure uncertainty of the well to be analyzed:

[0081] Formation pores, collapse and fracture pressures are the basic data for wellbore structure design. According to the special geological conditions of deep well complex formations, Monte Carlo and uncertainty theory can be used to obtain different types of formation pressures p t The formation pressure profile with credibility and the formation pressure curve with cumulative probability j0 (expressed in equivalent drilling fluid density) are expressed as follows:

[0082]

[0083] In the formula, p t Represents different types of formation pressure, when t=p p Indicates the formation pore pressure, t = p cmin Indicates the minimum formation collapse pressure, t = p cmax Indicates the maximum formation collapse pressure, t = p f Indicates the formation fracture pressure;

[0084] According to probability statistics theory, the probability density function p of the formation pressure at each depth is t(h) [p t(h) ] and the cumulative probability distribution function F t(h) [p t(h) ]The analytical solution expression is as follows:

[0085]

[0086]

[0087] In the formula,

[0088] Through the above steps, a probability distribution model of the formation pressure (including formation pore pressure, formation fracture pressure, and formation collapse pressure) of the well to be analyzed with depth can be established.

[0089] Furthermore, in step 2 of this solution, the upper and lower limits of safe drilling fluid density of the well to be analyzed are determined according to the pressure constraint criterion. Step 2 of this solution is designed in this way to facilitate the realization of reasonable wellbore structure design. The upper and lower limits of safe drilling fluid density include: the lower limit value of anti-blowout drilling fluid density ρ k(h) , Lower limit of drilling fluid density for preventing wellbore collapse ρ c1(h) , Upper limit value of drilling fluid density for preventing wellbore collapse ρ c2(h) , the upper limit value of drilling fluid density to prevent differential pressure sticking ρ sk(h) and the upper limit of the density of the anti-lost drilling fluid ρ L(h) ;like Figure 1 As shown, specifically:

[0090] Step 2: Establishment of safe drilling fluid density window for the well to be analyzed:

[0091] According to the pressure constraint criterion, the expressions for determining the upper and lower limits of safe drilling fluid density are as follows:

[0092] (1) Lower limit of drilling fluid density for preventing well kick ρ k(h) :

[0093] ρ k(h) =p t(h) +S b +Δρ,t=p p Indicates the formation pore pressure (4)

[0094] (2) Lower limit of drilling fluid density for preventing wellbore collapse ρ c1(h) and the upper limit of drilling fluid density ρ c2(h) :

[0095] ρ c1(h) =p t(h) +S b ,t=p cmin Indicates the minimum collapse pressure of the formation (5)

[0096] ρ c2(h) =p t(h) -S g ,t=p cmax Indicates the maximum collapse pressure of the formation (6)

[0097] (3) Upper limit of drilling fluid density ρ to prevent differential pressure sticking sk(h) :

[0098] t=p p Indicates the formation pore pressure (7)

[0099] (4) Upper limit of drilling fluid density for preventing leakage ρ L(h) :

[0100] ρ L(h) =p t(h) -S g -S f -S w -S c ,t=p f Indicates formation fracture pressure (8)

[0101] In the formula, S b is the pumping pressure coefficient, g / cm 3 ; S g is the excitation pressure coefficient, g / cm 3 ; Δρ is the additional drilling fluid density, g / cm 3 ; S f Increase the safety of formation fracture pressure, g / cm 3 ; S w Adding value to deepwater drilling fluid safety, g / cm 3 ; S c is the cycle pressure loss coefficient, g / cm 3 ; S k Well kick allowance, g / cm 3 ; ΔP is the allowable value of differential pressure for drilling, MPa; h pmax is the depth of the maximum formation pore pressure in the open hole section, m; h is the well depth, m.

[0102] Furthermore, in step 3 of this solution, based on the upper and lower limits of safe drilling fluid density and its distribution state, the risk of well kick, well wall collapse, drilling leakage, and differential pressure sticking at depth h are determined based on the reliability theory of generalized stress and strength interference. Step 3 of this solution is designed in this way to help improve the reliability of the quantitative assessment of the wellbore structure solution risk. Figure 1 As shown, specifically:

[0103] Step 3: Conduct a quantitative risk assessment for a specific wellbore structure solution:

[0104] According to the upper and lower limits of safe drilling fluid density and its distribution state, there are four risks: well kick risk R k 、Risk of well wall collapse R c , Drilling leakage risk L , Risk of drill bit stuck due to differential pressure sk Based on the reliability theory of generalized stress and strength interference, it is defined as follows:

[0105]

[0106]

[0107]

[0108] R L(h) =P(ρ d >ρ L(h) )=F ρL(h) (ρ d ) (12)

[0109] In the formula, R k(h) , R c(h) , R sk(h) , R L(h) They represent the risk of well kick, wellbore collapse, drilling leakage, and differential pressure sticking at depth h, respectively; ρ d is the density of drilling fluid during drilling, g / cm 3 .

[0110] Furthermore, in step 3 of this solution, after the risk quantitative assessment is performed on a specific wellbore structure solution of the well to be analyzed, the following steps are also included:

[0111] Step 4: Based on the risk assessment results of the wellbore structure plan, if the risk assessment result is less than the risk preset value, a specific wellbore structure plan is selected; if the risk quantitative assessment result is greater than or equal to the risk preset value, the construction parameters of the wellbore structure plan are optimized. Step 4 of this plan is designed in this way to reduce the risk of drilling projects. Figure 1 As shown, specifically:

[0112] Step 4: Based on the risk assessment results, optimize the construction parameters to reduce the risks:

[0113] If the risk assessment result exceeds the existing risk, the construction parameters are adjusted (such as optimizing the design of drilling fluid performance and density, and finely controlling drilling parameters, reducing suction and agitation pressure, etc.), and the influence of each main construction parameter on the risk of specific wellbore structure design scheme is analyzed. The mutual restraint relationship between the main construction parameters, casing layers and depth and other factors and the downhole engineering risks is determined, and the risk is reduced by optimizing the construction parameters.

[0114] Furthermore, after step 4 of this solution, the following steps are also included:

[0115] Step 5: Based on the principle of lenient at the top and strict at the bottom and risk sharing, establish a wellbore structure design plan; the wellbore structure design plan includes:

[0116] (1) Establishment of the depth range below the surface casing;

[0117] (2) Establishment of the bandwidth of the first vertical strip;

[0118] (3) extension and folding of the belt;

[0119] (4) Establishment of casing layers and depth range.

[0120] Step 5 of this plan proposes the principle of upper leniency and lower strictness and risk sharing in view of the special drilling geological conditions of deep wells with complex formations. The upper casing shares the risk of the lower casing as much as possible, thereby reducing the risk of construction operations in the harsh geological environment below. Figure 1 As shown, specifically:

[0121] Step 5: Based on the principle of leniency at the top and strictness at the bottom and risk sharing, a wellbore structure design scheme based on multi-objective optimization is proposed:

[0122] For deep well drilling in complex formations, due to the limited understanding of formation information, in order to leave a larger adjustment space for subsequent drilling, based on the principle of wide at the top and strict at the bottom and risk sharing, a top-down wellbore structure design method is adopted, so that each layer of casing is drilled to the deepest, and the upper casing bears as much risk of the lower casing as possible, which can maximize the guarantee of drilling safety; at the same time, if the drilling encounters an abnormally complex formation, the probability of complex drilling accidents can be reduced by adding a layer of spare casing.

[0123] The mud density upper and lower limit profiles with credibility established according to the above steps are as follows: Figure 2 As shown in the figure They represent the lower limit curves of mud density with cumulative probabilities j0 and j1, They are the upper limit curves of mud density with cumulative probabilities j0 and j1 respectively. The credibility of the upper and lower limit profiles of safe mud density is |j1-j0|×100%.

[0124] (1) Establishment of the depth range below the surface casing (width of the first horizontal zone)

[0125] Based on the formation lithology data and the reference to the surface casing depth data of adjacent wells, the surface casing depth range is determined to be D 11 ~D 12 (D 11 <D 12 );Depth range B1=D 12 -D 11 Defined as the bandwidth of the first horizontal band, and called D 11 is the top edge of the horizontal strip, D 12 for the bottom edge;

[0126] (2) Establishment of the first vertical stripe bandwidth

[0127] Extend the horizontal strip with bandwidth B1 horizontally, and the strips are respectively aligned with the curve and Intersecting at four points And M1 is defined as the bandwidth of the first vertical band:

[0128]

[0129] Similar to horizontal stripes, For this reason, the top edge of the vertical strip, for the bottom edge;

[0130] (3) Extension and folding of belt

[0131] Similar to the establishment method of the first horizontal strip and the first vertical strip, the first vertical strip is extended downward to align with the curve The intersection produces the second horizontal strip, and so on, the strips extend and fold in a step-like manner until the final well depth; the calculation formula for the width of the vertical strips and horizontal strips during the extension and folding process is:

[0132]

[0133] Where, L -1 is the inverse function of L, n is the total number of casing layers;

[0134] (4) Establishment of casing layers and depth range

[0135] From the above, we can see that the design results of the casing layer and the bottom depth are no longer a single value, but a range. The bottom depth range of each layer of casing is the top and bottom of the corresponding horizontal strip. And the casing layer may also change. From the design results (such as Figure 2 From Table 1), we can see that the deepest depth D of the fourth level casing is 42 It is possible to go directly to the final well depth D5, thereby reducing the number of casing layers from the original 5 to 4. Figure 2 As shown by the dotted step line, the current three-layer casing depth is greater than D1 * 、D2 * and D3 * When the design requirements are met, only 4 layers of casing are needed (as shown in Table 2).

[0136] Table 1 Casing layer and depth design results

[0137] Casing level Down depth or down depth range Credibility Surface casing <![CDATA[D 11 ~D 12 ]]> Technical casing 1 <![CDATA[D 21 ~D 22 ]]> <![CDATA[|j1-j0|×100%]]> Technical casing 2 <![CDATA[D 31 ~D 32 ]]> <![CDATA[|j1-j0|×100%]]> Technical casing 3 <![CDATA[D 41 ~D 42 ]]> <![CDATA[|j1-j0|×100%]]> Oil layer casing (or open hole completion) <![CDATA[D5]]> <![CDATA[|j1-j0|×100%]]>

[0138] Table 2 Requirements for each casing layer and depth of the four-layer scheme

[0139] 4-level solution Down depth or down depth range Credibility Surface casing <![CDATA[D1 * ~D 12 ]]> Technical casing 1 <![CDATA[D2 * ~D 21 ]]> <![CDATA[|j1-j0|×100%]]> Technical casing 2 <![CDATA[D3 * ~D 32 ]]> <![CDATA[|j1-j0|×100%]]> Oil layer casing (or open hole completion) <![CDATA[D5]]> <![CDATA[|j1-j0|×100%]]>

[0140] The technical solution of the present invention is further introduced below:

[0141] Based on the quantitative description method of the complex geological environment with uncertainty in deep oil and gas drilling, a reliable formation pressure profile of the well to be analyzed is constructed. On this basis, combined with the pressure constraint criterion of the open hole section, a safe drilling fluid density window for quantitatively evaluating the potential risks of the wellbore structure scheme is constructed; then, combined with the reliability theory method, a risk quantitative assessment is performed on any set of wellbore structure schemes; if the risk is evaluated to exist, the influence of each main construction parameter on the potential risk of the specific scheme is analyzed by adjusting the construction parameters (such as optimizing the design of drilling fluid performance and density, and finely controlling the drilling parameters, reducing the suction and agitation pressure, etc.), and the mutual constraint relationship between the main construction parameters, casing layers and depth and the downhole engineering risks is determined; finally, based on the principle of risk coordination and lenient at the top and strict at the bottom, a wellbore structure design method based on multi-objective optimization suitable for complex formations in deep wells is established by using methods such as decision trees.

[0142] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0143] 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 method for designing a wellbore structure in a deep well with complex formations based on multi-objective optimization, characterized in that: include: Step 1: Quantitative description of the uncertainty of formation pressure of the well to be analyzed; Step 2: Establishing a safe drilling fluid density window for the well to be analyzed, including: determining the upper and lower limits of the safe drilling fluid density for the well to be analyzed according to the pressure constraint criterion; The safe drilling fluid density upper and lower limits include: anti-kickback drilling fluid density lower limit value ρ k(h) , Lower limit of drilling fluid density for preventing wellbore collapse ρ c1(h) , Upper limit value of drilling fluid density for preventing wellbore collapse ρ c2(h) , the upper limit value of drilling fluid density to prevent differential pressure sticking ρ sk(h) and the upper limit of the density of the anti-lost drilling fluid ρ L(h) ; Determining the upper and lower limits of safe drilling fluid density of the well to be analyzed according to the pressure constraint criterion includes: (1) Lower limit of drilling fluid density for preventing well kick ρ k(h) : ρ k(h) =p t(h) +S b +△ρ, t=p p Indicates the formation pore pressure (4) (2) Lower limit of drilling fluid density for preventing wellbore collapse ρ c1(h) and the upper limit of drilling fluid density ρ c2(h) : ρ c1(h) =p t(h) +S b , t=p cmin Indicates the minimum collapse pressure of the formation (5) ρ c2(h) =p t(h) -S g , t=p cmax Indicates the maximum collapse pressure of the formation (6) (3) Upper limit of drilling fluid density ρ to prevent differential pressure sticking sk(h) : (4) Upper limit of drilling fluid density for preventing leakage ρ L(h) : ρ L(h) =p t(h) -S g -S f -S w -S c , t=p f Indicates formation fracture pressure (8) In the formula, S b is the pumping pressure coefficient, g / cm 3 ; S g is the excitation pressure coefficient, g / cm 3 ; △ρ is the additional drilling fluid density, g / cm 3 ; S f Increase the safety of formation fracture pressure, g / cm 3 ; S w Adding value to deepwater drilling fluid safety, g / cm 3 ; S c is the cycle pressure loss coefficient, g / cm 3 ; S k Well kick allowance, g / cm 3 ; △P is the allowable value of differential pressure for drilling, MPa; h pmax is the depth of the maximum formation pore pressure in the open hole section, m; h is the well depth, m; Step 3: Performing a quantitative risk assessment on a specific wellbore structure scheme for the well to be analyzed; if the result of the quantitative risk assessment is less than the preset risk value, then selecting a specific wellbore structure scheme; if the result of the quantitative risk assessment is greater than or equal to the preset risk value, then redesigning the wellbore structure scheme; the quantitative risk assessment on a specific wellbore structure scheme for the well to be analyzed includes: According to the upper and lower limits of safe drilling fluid density and its distribution state, the risk of well kick, well wall collapse, drilling leakage and differential pressure sticking at depth h are determined based on the reliability theory of generalized stress and strength interference: In the formula, R k(h) , R c(h) , R sk(h) , R L(h) They represent the risk of well kick, wellbore collapse, drilling leakage, and differential pressure sticking at depth h, respectively; ρ d is the drilling fluid density during drilling, g / cm 3 ; Step 4: Based on the risk assessment result of the wellbore structure scheme, if the risk assessment result is less than the risk preset value, a specific wellbore structure scheme is selected; if the risk quantitative assessment result is greater than or equal to the risk preset value, the construction parameters of the wellbore structure scheme are optimized.

2. The method for designing a wellbore structure in a deep well with complex formations based on multi-objective optimization according to claim 1, characterized in that: In step 1, the uncertainty of the formation pressure of the well to be analyzed is quantitatively described, including: Using Monte Carlo and uncertainty theory, we can obtain the formation pressure p of different types of wells to be analyzed. t Formation pressure profile with credibility; A probability distribution model of formation pressure with depth in the well to be analyzed is established.

3. The method for designing a deep well structure in a complex formation based on multi-objective optimization according to claim 2, characterized in that: The Monte Carlo and uncertainty theory are used to obtain the formation pressure p of different types of wells to be analyzed. t Credible formation pressure profiles, including: The expression of the formation pressure curve with cumulative probability j0 is: In the formula, p t Represents different types of formation pressure, when t = p p Indicates the formation pore pressure, t = p cmin Indicates the minimum formation collapse pressure, t = p cmax Indicates the maximum formation collapse pressure, t = p f Indicates formation fracture pressure; According to probability statistics theory, the probability density function p of the formation pressure at each depth is t(h) [p t(h) ] and the cumulative probability distribution function F t(h) [p t(h) ]The analytical solution expression is as follows: In the formula, 4. The method for designing a wellbore structure in a deep well with complex formations based on multi-objective optimization according to claim 1, characterized in that: The construction parameters include: drilling fluid performance parameters, drilling fluid density parameters and / or drilling fluid drilling parameters.

5. The method for designing a wellbore structure in a deep well with complex formations based on multi-objective optimization according to claim 1, characterized in that: After step 4, the method further includes: Step 5: Based on the principle of lenient at the top and strict at the bottom and risk sharing, establish a wellbore structure design plan; the wellbore structure design plan includes: (1) Establishment of the depth range below the surface casing; (2) Establishment of the bandwidth of the first vertical strip; (3) extension and folding of the belt; (4) Establishment of casing layers and depth range.

6. The method for designing a wellbore structure in a deep well with complex formations based on multi-objective optimization according to claim 5, characterized in that: The (1) establishment of the depth range below the surface casing includes: Based on the formation lithology data and the reference to the surface casing depth data of adjacent wells, the surface casing depth range is determined to be D 11 ~D 12 (D 11 <D 12 );Depth range B1=D 12 -D 11 Defined as the bandwidth of the first horizontal band, and called D 11 is the top edge of the horizontal strip, D 12 for the bottom edge; The (2) establishment of the first vertical stripe bandwidth includes: Extend the horizontal strip with bandwidth B1 horizontally, and the strips are respectively aligned with the curve and Intersecting at four points And M1 is defined as the bandwidth of the first vertical band: Similar to horizontal stripes, For this reason, the top edge of the vertical strip, for the bottom edge; The (3) extension and folding of the belt comprises: Similar to the establishment method of the first horizontal strip and the first vertical strip, the first vertical strip is extended downward to coincide with the curve L j1 The intersection produces the second horizontal strip, and so on, the strips extend and fold in a step-like manner until the final well depth; the calculation formula for the width of the vertical strips and horizontal strips during the extension and folding process is: Where, L -1 is the inverse function of L, n is the total number of casing layers; The (4) establishment of casing layers and depth range includes: The lower depth range of each layer of casing is the top and bottom edges of the corresponding horizontal strip.

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