CN117072157A - Method and system for quantitatively predicting salt-paste layer ground stress based on stuck drilling accident - Google Patents
Method and system for quantitatively predicting salt-paste layer ground stress based on stuck drilling accident Download PDFInfo
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- 238000005553 drilling Methods 0.000 title claims abstract description 120
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- 150000003839 salts Chemical class 0.000 claims abstract description 106
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- E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
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Abstract
The invention relates to a method and a system for quantitatively predicting the ground stress of a salt paste layer based on a drilling sticking accident, wherein the method comprises the following steps: determining drilling fluid density and salt bed borehole shrinkage rate according to the drilling log data; determining creep parameters according to a salt paste layer creep test experiment; establishing a relation model of the radial stress of the well periphery, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore based on the plane strain assumption condition; establishing a radial stress and salt paste layer ground stress relation model by combining stress coordinate system conversion; and establishing a relation model of the radial stress of the well periphery and the density, creep parameter and well shrinkage rate of the drilling fluid under the plane strain assumption condition, carrying out equivalent treatment by combining the relation model of the radial stress and the salt-paste layer ground stress established by converting a stress coordinate system, and determining the two-way horizontal ground stress of the salt-paste layer. The method can realize quantitative prediction of the two-way horizontal ground stress of the salt paste layer, and reduces underground complex accidents caused by error evaluation of drilling fluid tightness.
Description
Technical Field
The invention belongs to the technical field of petroleum and natural gas drilling, and particularly relates to a method and a system for quantitatively predicting the ground stress of a salt paste layer based on a stuck drilling accident.
Background
The deep land is an important successor field of energy, 39% of residual petroleum and 57% of residual natural gas are distributed in the deep land, and deep and ultra-deep oil and gas resources become the main battlefield of future oil and gas strategy. The salt paste layer is a natural good cover layer of oil and gas reservoir, however, the salt paste layer has strong fluidity under high-temperature and high-pressure environment, is extremely easy to cause necking and collapse of a well hole, causes complex accidents such as blocking, sticking, casing deformation and the like when drilling underground, even causes the risk of well scrapping, and brings serious challenges to safe drilling, so that the salt paste layer drilling is always a technical problem of world grade.
At present, a reaming while drilling technology is often adopted to drill through the salt paste layer in the salt paste layer drilling process, so that creep shrinkage displacement of the salt paste layer is reduced, and complex conditions such as drilling sticking and shrinkage are reduced or avoided; meanwhile, the thickness of the cement sheath can be increased, the capability of the cement sheath system for resisting stratum creep is improved, the well cementation quality is improved, and the oil layer casing is protected, so that the influence caused by creep of the salt paste layer is made up, and the purpose of changing time in space is achieved.
However, current computational models that determine reasonable drilling fluid densities typically assume uniform stress, which results in erroneous assessment of reasonable values of drilling fluid density, thereby affecting the effectiveness of the reaming while drilling operation. Therefore, reasonable judgment of the ground stress of the salt paste layer becomes a bottleneck problem which restricts the reaming while drilling operation effect and needs to be solved urgently.
Disclosure of Invention
Aiming at the problems, the invention aims to reasonably judge and determine the ground stress state of the salt paste layer when the salt paste layer is drilled, and provide guidance for determining reasonable drilling fluid density during reaming while drilling operation.
The technical scheme adopted by the invention is as follows: a method for quantitatively predicting salt-paste layer ground stress based on a stuck drilling accident, the method comprising the following steps: determining drilling fluid density and salt bed borehole shrinkage rate according to the drilling log data; determining creep parameters according to a salt paste layer creep test experiment; establishing a relation model of the radial stress of the well periphery, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore based on the plane strain assumption condition; establishing a radial stress and salt paste layer ground stress relation model by combining stress coordinate system conversion; and establishing a relation model of the radial stress of the well periphery and the density, creep parameter and well shrinkage rate of the drilling fluid under the plane strain assumption condition, carrying out equivalent treatment by combining the relation model of the radial stress and the salt-paste layer ground stress established by converting a stress coordinate system, and determining the two-way horizontal ground stress of the salt-paste layer.
Further, the salt paste layer creep test experiment comprises: placing a standard rock sample on a true triaxial experimental instrument, wrapping a thermoplastic pipe outside the rock sample, placing a sensor on the outer side of the thermoplastic pipe, adjusting the position of a sensor probe, and then placing the sensor probe in the center of a base; the axial bias stress and confining pressure are loaded in a grading way through a servo control system on a true triaxial experimental instrument; and after the standard rock sample is destroyed, closing the servo control system, and unloading the axial bias force and the confining pressure.
Further, the standard rock sample size is 50mm×100mm; the step loading of axial bias stress and confining pressure by a servo control system on a true triaxial experimental instrument comprises the following steps: by controlling principal stress sigma 1 From the initial stress σ, in the case of =125 MPa unchanged 3 =120 MPa, offset stress difference σ 1 -σ 3 Starting with =5mpa, each stage decreases the confining pressure by 5MPa while increasing the deflection stress difference by 5 MPa.
Further, the determining creep parameters according to the salt paste layer creep test experiment comprises: and according to the salt paste layer creep test experiment, counting creep rate and bias stress difference of all rock samples, drawing point diagrams of the salt paste layer rock sample creep rate and bias stress difference at different depths, and fitting to determine creep parameters.
Further, the establishing a relation model of the circumferential radial stress of the well, the drilling fluid density, the creep parameter and the shrinkage rate of the well hole based on the plane strain hypothesis condition comprises the following steps: according to the theory of continuous medium mechanics, determining a basic differential equation of salt paste layer creep, including a balance equation, a geometric equation and boundary conditions; and (3) solving a basic differential equation, and determining a relation model of the radial stress around the well, the drilling fluid density, the creep parameter and the well bore shrinkage rate.
Further, the equilibrium equation is:σ r representing the circumferential radial stress, sigma, of the well θ Representing the circumferential tangential stress of the well, r representing the distance of the formation from the center of the borehole; the saidThe geometric equation is:
ε r indicating the circumferential radial strain of the well epsilon θ Indicating the circumferential tangential strain of the well, u indicating the displacement rate on the well wall; the boundary conditions are:
P m representing the fluid column pressure, sigma, in the well bore H Representing the maximum horizontal ground stress, sigma h Representing a minimum horizontal ground stress; p (P) m ＝ρ m gH，ρ m Represents the drilling fluid density, and H represents the drilling fluid depth.
Further, the basic differential equation is solved, and the relation model for determining the radial stress around the well, the density of drilling fluid, creep parameters and the shrinkage rate of the well is as follows:
wherein->a represents the wellbore radius, A, B the rheological constant; c represents a predetermined constant, μ c The Poisson's ratio of the salt paste layer is represented by E, the activation energy of the salt paste layer is represented by R, the ideal gas constant is represented by R, and the absolute temperature is represented by T.
Further, the plane strain assumption includes a plane strain basic assumption along the wellbore direction, specifically: assuming that the salt formation is isotropic; considering the wellbore as an infinitely long cylinder, assuming that no strain is created during the drilling process along the axis of the wellbore; when the stress state of the surrounding rock of the well wall is below the expansion boundary line of the salt rock and the salt rock is in an elastic stress state, the ground stress of the salt rock stratum is nonuniform.
Further, the establishing a radial stress and salt paste layer ground stress relation model by combining stress coordinate system conversion comprises the following steps: dividing wellbore ambient load under non-uniform stressThe solution is that the three conditions of internal pressure action only, bidirectional stress compression and pulling and pressing combined action are adopted: radial stress sigma of well circumference when only subjected to internal pressure r1 The method comprises the following steps:
well circumferential radial stress sigma of two-way stress compression r2 The method comprises the following steps:
drawing-pressing combined well circumferential radial stress sigma r3 The method comprises the following steps:
θ represents the angle between the X axis and the line connecting any point of the well and the origin in the polar coordinates; obtaining the radial stress of the periphery of the well under the action of non-uniform ground stress>The equation of (2) is:
assuming that the deformation is smaller in the single stress state around the shaft, the stress relation model for determining the radial stress and the salt paste layer ground stress at the infinite distance from the shaft by using the stress superposition principle is as follows:
further, establishing a relation model of the radial stress of the well periphery and the density of drilling fluid, creep parameters and the shrinkage rate of the well hole under the plane strain assumption condition, performing equivalent treatment on the relation model of the radial stress and the ground stress of the salt deposit layer by combining stress coordinate system conversion, and determining the two-way horizontal ground stress of the salt deposit layer comprises the following steps:
building plane strain hypothesis conditionsThe relationship model of the radial stress around the vertical shaft and the density of drilling fluid, creep parameter and the shrinkage rate of the borehole is equivalent processed by establishing the relationship model of the radial stress and the ground stress of the salt paste layer by combining the conversion of the stress coordinate system, namely sigma' r ＝σ r Respectively substituting sigma' r Sum sigma r Is obtained by the relation model of (1):
further, the salt-paste layer well bore diameter shrinkage rate is:
n＝S 0 /BS·T 0 n represents the well bore shrinkage rate, S 0 Representing the shrinkage deformation of the borehole during the drilling or the hanging of the drill, BS representing the borehole size, T 0 Indicating the wellbore safety time.
Further, the borehole shrinkage deformation, the borehole size and the drilling fluid density during the drilling or the hanging are all determined according to the drilling log data, specifically: judging whether a drilling sticking accident occurs in the salt-gypsum layer section according to the drilling log data; if the drilling sticking accident occurs, the shrinkage deformation of the well hole, the size of the well hole and the density of the drilling fluid are determined according to the blocking of the salt paste layer and the drilling sticking data.
In addition, the invention also provides a system for quantitatively predicting the ground stress of the salt paste layer based on the stuck drilling accident, which comprises: the system comprises a first determining module, a second determining module, a first establishing module, a second establishing module and an equivalent processing module; the first determining module is used for determining the drilling fluid density and the salt-paste layer borehole diameter reduction rate according to the drilling log data; the second determining module is used for determining creep parameters according to a salt paste layer creep test experiment; the first building module is used for building a relation model of the circumferential radial stress of the well, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore based on plane strain hypothesis conditions; the second establishing module is used for establishing a radial stress and salt paste layer ground stress relation model by combining stress coordinate system conversion; the equivalent processing module is used for establishing a relation model of the radial stress of the well periphery, the density of drilling fluid, creep parameters and the shrinkage rate of the well hole under the condition of plane strain assumption, carrying out equivalent processing on the relation model of the radial stress and the ground stress of the salt deposit layer by combining stress coordinate system conversion, and determining the two-way horizontal ground stress of the salt deposit layer.
Further, the second determining module comprises a statistics unit and a fitting unit, wherein the statistics unit is used for counting all rock sample creep rates and bias stress differences according to a salt-paste layer creep test experiment; and the fitting unit is used for drawing point line graphs of salt-paste layer rock-like creep rate and bias stress difference at different depths and fitting and determining creep parameters.
Further, the first establishing module comprises a first determining unit and a solving unit, wherein the determining unit is used for determining a basic differential equation of the salt paste layer creep according to the continuous medium mechanics theory, and the basic differential equation comprises a balance equation, a geometric equation and a boundary condition; the solving unit is used for solving a basic differential equation and determining a relation model of the circumferential radial stress of the well, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore.
Further, the second establishing module comprises a decomposing unit and a second determining unit; the decomposing unit is used for decomposing the load around the shaft under the action of non-uniform stress into three conditions of only internal pressure action, two-way stress compression and pulling and pressing combined action; the second determining unit is used for determining a relation model of radial stress and salt paste layer ground stress at an infinite distance from the shaft by using a stress superposition principle on the assumption that deformation is small under an independent stress state around the shaft.
The method comprehensively utilizes field data analysis and theoretical model deduction to reasonably determine the ground stress state of the salt paste layer, and provides a reference for determining reasonable drilling fluid density during reaming while drilling operation. Meanwhile, the method for quantitatively predicting the ground stress of the salt paste layer based on the stuck drilling accident can realize quantitative prediction of the two-way horizontal ground stress of the salt paste layer, is beneficial to improving the reaming operation effect while drilling, reduces underground complex accidents caused by error evaluation of the drilling fluid tightness, shortens the drilling period of the salt paste layer and saves the drilling construction cost.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for quantitatively predicting the ground stress of a salt paste layer based on a stuck drilling accident;
FIG. 2 is a schematic illustration of deformation between a drilling assembly and wellbore dimensions during creep section drilling;
FIG. 3 is a plot of a dotted line fit of salt bed creep rate and bias stress differences;
FIG. 4 is a diagram of a mechanical model around a salt bed wellbore;
FIG. 5a is a schematic diagram of superimposed forces around a salt deposit wellbore when only internal pressure is applied; FIG. 5b is a schematic diagram of superimposed forces around a salt-paste layer wellbore during bi-directional stress compression; FIG. 5c is a schematic diagram of superimposed forces around a salt-paste layer wellbore when the pulling and pressing forces act together;
FIG. 6 is a schematic diagram of a system for quantitatively predicting the ground stress of a salt deposit based on a stuck drilling accident.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention designs a method for quantitatively predicting the ground stress of a salt paste layer based on a drilling sticking accident, which is shown in figure 1 and comprises the following steps: determining drilling fluid density and salt bed borehole shrinkage rate according to the drilling log data; determining creep parameters according to a salt paste layer creep test experiment; establishing a relation model of the radial stress of the well periphery, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore based on the plane strain assumption condition; establishing a radial stress and salt paste layer ground stress relation model by combining stress coordinate system conversion; and establishing a relation model of the radial stress of the well periphery and the density, creep parameter and well shrinkage rate of the drilling fluid under the plane strain assumption condition, carrying out equivalent treatment by combining the relation model of the radial stress and the salt-paste layer ground stress established by converting a stress coordinate system, and determining the two-way horizontal ground stress of the salt-paste layer.
Specifically, the well log data comprises data such as a creep section depth range, a well bore size, a drilling speed, a well bore safety time, a drilling fluid density, a well bore diameter reduction deformation amount during drilling sticking or hanging sticking, and the like, and a salt paste layer well bore diameter reduction rate calculation formula is as follows: n=s 0 /BS·T 0 N represents the well bore shrinkage rate, S 0 Representing the shrinkage deformation of the borehole during the drilling or the hanging of the drill, BS representing the borehole size, T 0 Indicating the wellbore safety time.
The method for determining the drilling fluid density and the salt-paste layer borehole shrinkage rate according to the drilling log data comprises the following steps: judging whether a drilling sticking accident occurs in the salt-gypsum layer section according to the drilling log data; if the drilling sticking accident occurs, the diameter reduction deformation of the well hole, the well hole size and the drilling fluid density during the drilling sticking or the hanging of the drilling sticking are determined according to the blocking and the drilling sticking data of the salt paste layer, and then the diameter reduction rate of the well hole of the salt paste layer is determined according to the diameter reduction deformation of the well hole and the well hole size during the drilling sticking or the hanging of the drilling sticking. FIG. 2 is a schematic diagram of the amount of deformation between the drill assembly and the borehole size during creep section drilling, where the amount of deformation in FIG. 2 is the difference between the borehole size and the outside diameter of the drill. Specifically, determining creep parameters according to a salt-paste layer creep test experiment includes: the salt paste layer creep test experiment comprises the following steps: step 1: and (5) placing the completely cut standard rock sample on a true triaxial experimental instrument, and assembling equipment and pipelines. During assembly, the rock sample is wrapped with the thermoplastic pipe, the sensor is arranged outside the thermoplastic pipe, and the sensor probe is arranged after the position of the sensor probe is adjustedAt the center of the base, the standard rock sample size is 50mm×100mm; step 2: axial bias stress and confining pressure are loaded in stages through a servo control system on a true triaxial experimental instrument, and main stress sigma is controlled 1 From the initial stress σ, in the case of =125 MPa unchanged 3 =120 MPa, offset stress difference σ 1 -σ 3 Starting with =5 MPa, each stage is reduced by 5MPa confining pressure (σ 3 ) Is increased by 5MPa (sigma) 1 -σ 3 ) Thereby ensuring the main stress to be unchanged and gradually increasing the axial bias stress of 5 MPa; step 3: after the rock sample is destroyed, the experimental instrument is stopped, the servo system is closed after the experimental instrument is cooled to the room temperature, the axial pressure and the confining pressure are unloaded, and the experiment is finished. Determining creep parameters according to a salt paste layer creep experiment, including: and (5) calculating creep rate and bias stress difference of all rock sample salt paste layers. And drawing point line graphs of salt-paste layer rock-like creep rate and deviation stress difference at different depths, and fitting to determine creep parameters as shown in fig. 2. In FIG. 3, the abscissa indicates the differential deflection stress (σ 1 -σ 3 ) The ordinate is the salt paste creep rate epsilon, a plurality of groups of data (salt paste creep rate and bias stress difference) are obtained through fitting the salt paste creep experiment, and the relation between the salt paste creep rate and the bias stress difference is obtained as follows: y=1×10 -5 x 3 -5×10 -9 x 2 +2×10 -7 x-6×10 -7 The correlation coefficient is R 2 =0.9974. The creep parameter was determined to be a=0.071 and b=0.65 from the fitting result of fig. 3.
Specifically, establishing a relationship model of the circumferential radial stress of the well, the drilling fluid density, the creep parameter and the borehole shrinkage rate based on the plane strain hypothesis condition comprises the following steps: the plane strain hypothesis includes a plane strain base hypothesis along the wellbore direction: (1) assuming that the salt formation is isotropic; (2) Considering the wellbore as an infinitely long cylinder, assuming that no strain is created during the drilling process along the axis of the wellbore; (3) When the stress state of the surrounding rock of the well wall is below the expansion boundary line of the rock salt, the rock salt is in an elastic stress state, and the ground stress of the rock salt stratum is nonuniform.
FIG. 4 is a graph of a mechanical model around a salt-slurry wellbore including a basic differential equation for determining salt-slurry creep based on continuous medium mechanics theory, includingBalance equations, geometric equations and boundary conditions; the equilibrium equation is:σ r representing the circumferential radial stress, sigma, of the well θ Representing the circumferential tangential stress of the well, r representing the distance of the formation from the center of the borehole; the geometric equation is: />ε r Indicating the circumferential radial strain of the well epsilon θ Indicating the circumferential tangential strain of the well, u indicating the displacement rate on the well wall; the boundary conditions are:P m representing the fluid column pressure, sigma, in the well bore H Representing the maximum horizontal ground stress, sigma h Representing the minimum horizontal ground stress, where P m ＝ρ m gH，ρ m Represents the drilling fluid density, and H represents the drilling fluid depth. Solving a basic differential equation, and determining a relation model of the radial stress of the well periphery and the density, creep parameter and the shrinkage rate of the well bore as follows:
wherein->a represents the wellbore radius, A, B the rheological constant; c represents a predetermined constant, μ c The Poisson's ratio of the salt paste layer is represented by E, the activation energy of the salt paste layer is represented by R, the ideal gas constant is represented by R, and the absolute temperature is represented by T.
Establishing a radial stress and salt layer ground stress relation model by combining stress coordinate system conversion, wherein fig. 5a is a schematic diagram of superposition of stress around a salt layer shaft when only internal pressure acts; FIG. 5b is a schematic diagram of superimposed forces around a salt-paste layer wellbore during bi-directional stress compression; FIG. 5c is a schematic diagram of superimposed forces around a salt-paste layer wellbore when the pulling and pressing forces act together; comprising decomposing the load surrounding the well bore under non-uniform stress into pressure-only stressesThree conditions of combined action of compression and tension and compression of two-way stress: (1) Radial stress sigma of well circumference when only subjected to internal pressure r1 The method comprises the following steps:(2) Well circumferential radial stress sigma of two-way stress compression r2 The method comprises the following steps: />(3) Drawing-pressing combined well circumferential radial stress sigma r3 The method comprises the following steps:
θ represents the angle between the X axis and the line connecting any point of the well and the origin in the polar coordinates;
obtaining the radial stress of the periphery of the well under the action of non-uniform ground stressThe equation of (2) is:
determining infinity from a wellbore using stress superposition principles (i.e.)The distance r of the formation from the borehole center tends to infinity) radial stress versus salt bed earth stress model is:
specifically, establishing a relation model of the radial stress of the well periphery, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore by using the plane strain assumption condition, performing equivalent treatment by combining the relation model of the radial stress and the ground stress of the salt deposit layer by converting a stress coordinate system, and determining the two-way horizontal ground stress of the salt deposit layer comprises the following steps:
establishing a relation model of the radial stress of the well periphery and the density, creep parameter and well shrinkage rate of the drilling fluid under the plane strain assumption condition, and performing equivalent treatment by combining the relation model of the radial stress and the salt-paste layer ground stress established by the conversion of a stress coordinate system, namely sigma r ＝σ r Respectively substituting sigma' r Sum sigma r Is obtained by the relation model of (1):
in addition, the invention also designs a system for quantitatively predicting the ground stress of the salt paste layer based on the stuck drilling accident, as shown in fig. 6, the system comprises: the system comprises a first determining module, a second determining module, a first establishing module, a second establishing module and an equivalent processing module; the first determining module is used for determining the drilling fluid density and the salt-paste layer borehole diameter reduction rate according to the drilling log data; the second determining module is used for determining creep parameters according to a salt paste layer creep test experiment; the first building module is used for building a relation model of the circumferential radial stress of the well, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore based on plane strain hypothesis conditions; the second establishing module is used for establishing a radial stress and salt paste layer ground stress relation model by combining stress coordinate system conversion; the equivalent processing module is used for establishing a relation model of the radial stress of the well periphery, the density of drilling fluid, creep parameters and the shrinkage rate of the well hole under the condition of plane strain assumption, carrying out equivalent processing on the relation model of the radial stress and the ground stress of the salt deposit layer by combining stress coordinate system conversion, and determining the two-way horizontal ground stress of the salt deposit layer.
Specifically, the second determining module comprises a statistics unit and a fitting unit, wherein the statistics unit is used for counting all rock sample creep rates and stress differences according to a salt-paste layer creep test experiment; and the fitting unit is used for drawing point diagrams of salt-paste layer rock-like creep rates and stress differences at different depths and fitting and determining creep parameters.
Specifically, the first establishing module comprises a first determining unit and a solving unit, wherein the determining unit is used for determining a basic differential equation of the salt paste layer creep according to the continuous medium mechanics theory, and the basic differential equation comprises a balance equation, a geometric equation and a boundary condition; the solving unit is used for solving a basic differential equation and determining a relation model of the circumferential radial stress of the well, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore.
Specifically, the second establishing module comprises a decomposing unit and a second determining unit; the decomposing unit is used for decomposing the load around the shaft under the action of non-uniform stress into three conditions of only internal pressure action, two-way stress compression and pulling and pressing combined action; the second determining unit is used for determining a relation model of radial stress and salt paste layer ground stress at an infinite distance from the shaft by using a stress superposition principle on the assumption that deformation is small under an independent stress state around the shaft.
Although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (16)
1. A method for quantitatively predicting salt-paste layer ground stress based on a stuck drilling accident, the method comprising the following steps:
determining drilling fluid density and salt bed borehole shrinkage rate according to the drilling log data;
determining creep parameters according to a salt paste layer creep test experiment;
establishing a relation model of the radial stress of the well periphery, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore based on the plane strain assumption condition;
establishing a radial stress and salt paste layer ground stress relation model by combining stress coordinate system conversion;
and establishing a relation model of the radial stress of the well periphery and the density, creep parameter and well shrinkage rate of the drilling fluid under the plane strain assumption condition, carrying out equivalent treatment by combining the relation model of the radial stress and the salt-paste layer ground stress established by converting a stress coordinate system, and determining the two-way horizontal ground stress of the salt-paste layer.
2. The method of claim 1, wherein the salt layer creep test experiment comprises:
placing a standard rock sample on a true triaxial experimental instrument, wrapping a thermoplastic pipe outside the rock sample, placing a sensor on the outer side of the thermoplastic pipe, adjusting the position of a sensor probe, and then placing the sensor probe in the center of a base;
the axial bias stress and confining pressure are loaded in a grading way through a servo control system on a true triaxial experimental instrument;
and after the standard rock sample is destroyed, closing the servo control system, and unloading the axial bias force and the confining pressure.
3. The method of claim 2, wherein the standard rock sample size is 50mm x 100mm; the step loading of axial bias stress and confining pressure by a servo control system on a true triaxial experimental instrument comprises the following steps:
by controlling principal stress sigma 1 From the initial stress σ, in the case of =125 MPa unchanged 3 =120 MPa, offset stress difference σ 1 -σ 3 Starting with =5mpa, each stage decreases the confining pressure by 5MPa while increasing the deflection stress difference by 5 MPa.
4. The method of claim 3, wherein the determining creep parameters from a salt bed creep test experiment comprises:
and according to the salt paste layer creep test experiment, counting creep rate and bias stress difference of all rock samples, drawing point diagrams of the salt paste layer rock sample creep rate and bias stress difference at different depths, and fitting to determine creep parameters.
5. The method of claim 1, wherein modeling the relationship of the well circumferential radial stress to the drilling fluid density, creep parameters, and the wellbore reduction rate based on the planar strain hypothesis conditions comprises:
according to the theory of continuous medium mechanics, determining a basic differential equation of salt paste layer creep, including a balance equation, a geometric equation and boundary conditions;
and (3) solving a basic differential equation, and determining a relation model of the radial stress around the well, the drilling fluid density, the creep parameter and the well bore shrinkage rate.
6. The method of claim 5, wherein the equilibrium equation is:
σ r representing the circumferential radial stress, sigma, of the well θ Representing the circumferential tangential stress of the well, r representing the distance of the formation from the center of the borehole;
the geometric equation is:
ε r indicating the circumferential radial strain of the well epsilon θ Indicating the circumferential tangential strain of the well, u indicating the displacement rate on the well wall;
the boundary conditions are:
P m representing the fluid column pressure, sigma, in the well bore H Representing the maximum horizontal ground stress, sigma h Representing a minimum horizontal ground stress;
ρ m ＝ρ m gH，ρ m represents the drilling fluid density, and H represents the drilling fluid depth.
7. The method of claim 6, wherein the solving the basic differential equation determines a relationship model of the radial stress around the well with the drilling fluid density, creep parameter, and the rate of shrinkage of the borehole as:
wherein->a represents the wellbore radius, A, B the rheological constant; c represents a predetermined constant, μ c The Poisson's ratio of the salt paste layer is represented by E, the activation energy of the salt paste layer is represented by R, the ideal gas constant is represented by R, and the absolute temperature is represented by T.
8. The method of any of claims 5-7, wherein the planar strain hypothesis comprises a planar strain base hypothesis along the wellbore direction, in particular:
assuming that the salt formation is isotropic;
considering the wellbore as an infinitely long cylinder, assuming that no strain is created during the drilling process along the axis of the wellbore;
when the stress state of the surrounding rock of the well wall is below the expansion boundary line of the salt rock and the salt rock is in an elastic stress state, the ground stress of the salt rock stratum is nonuniform.
9. The method of claim 1, wherein the modeling radial stress versus salt layer ground stress relationship in conjunction with stress coordinate system transformations comprises:
under the action of non-uniform stress, the surrounding load of the shaft is decomposed into three conditions of only internal pressure action, bidirectional stress compression and pulling and pressing combined action:
radial stress sigma of well circumference when only subjected to internal pressure r1 The method comprises the following steps:
well circumferential radial stress sigma of two-way stress compression r2 The method comprises the following steps:
pulling and pressing combined well circumference radial directionStress sigma r3 The method comprises the following steps:
θ represents the angle between the X axis and the line connecting any point of the well and the origin in the polar coordinates;
obtaining the radial stress of the periphery of the well under the action of non-uniform ground stressThe equation of (2) is:
assuming that the deformation is smaller in the single stress state around the shaft, the stress relation model for determining the radial stress and the salt paste layer ground stress at the infinite distance from the shaft by using the stress superposition principle is as follows:
10. the method of claim 9, wherein modeling the planar strain hypothesis conditions as a relationship between the radial stress around the well and the drilling fluid density, creep parameters, and the wellbore shrinkage rate, and modeling the radial stress and the salt-paste layer ground stress relationship in combination with the stress coordinate system transformation are equivalent, and determining the salt-paste layer bi-directional horizontal ground stress comprises:
establishing a relation model of the radial stress of the well periphery and the density, creep parameter and well shrinkage rate of the drilling fluid under the plane strain assumption condition, and performing equivalent treatment by combining the relation model of the radial stress and the salt-paste layer ground stress established by the conversion of a stress coordinate system, namely sigma' r ＝σ r Respectively substituting sigma' r Sum sigma r Is obtained by the relation model of (1):
11. the method of claim 1, wherein the salt bed wellbore reduction rate is:
n＝S 0 /BS·T 0 n represents the well bore shrinkage rate, S 0 Representing the shrinkage deformation of the borehole during the drilling or the hanging of the drill, BS representing the borehole size, T 0 Indicating the wellbore safety time.
12. The method of claim 11, wherein the borehole shrinkage deformation, the borehole size, and the drilling fluid density are determined from drilling log data, in particular:
judging whether a drilling sticking accident occurs in the salt-gypsum layer section according to the drilling log data;
if the drilling sticking accident occurs, the shrinkage deformation of the well hole, the size of the well hole and the density of the drilling fluid are determined according to the blocking of the salt paste layer and the drilling sticking data.
13. A system for quantitatively predicting salt-paste layer ground stress based on a stuck-at accident, the system comprising: the system comprises a first determining module, a second determining module, a first establishing module, a second establishing module and an equivalent processing module;
the first determining module is used for determining the drilling fluid density and the salt-paste layer borehole diameter reduction rate according to the drilling log data;
the second determining module is used for determining creep parameters according to a salt paste layer creep test experiment;
the first building module is used for building a relation model of the circumferential radial stress of the well, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore based on plane strain hypothesis conditions;
the second establishing module is used for establishing a radial stress and salt paste layer ground stress relation model by combining stress coordinate system conversion;
the equivalent processing module is used for establishing a relation model of the radial stress of the well periphery, the density of drilling fluid, creep parameters and the shrinkage rate of the well hole under the condition of plane strain assumption, carrying out equivalent processing on the relation model of the radial stress and the ground stress of the salt deposit layer by combining stress coordinate system conversion, and determining the two-way horizontal ground stress of the salt deposit layer.
14. The system of claim 13, wherein the second determination module comprises a statistics unit for counting all rock sample creep rates and bias stress differences according to a salt bed creep test experiment, and a fitting unit; and the fitting unit is used for drawing point line graphs of salt-paste layer rock-like creep rate and bias stress difference at different depths and fitting and determining creep parameters.
15. The system of claim 13, wherein the first build module comprises a first determination unit and a solution unit, the determination unit to determine basic differential equations of salt bed creep, including equilibrium equations, geometric equations, and boundary conditions, based on continuous medium mechanics theory; the solving unit is used for solving a basic differential equation and determining a relation model of the circumferential radial stress of the well, the density of drilling fluid, creep parameters and the shrinkage rate of the well bore.
16. The system of claim 13, wherein the second setup module comprises a decomposition unit and a second determination unit; the decomposing unit is used for decomposing the load around the shaft under the action of non-uniform stress into three conditions of only internal pressure action, two-way stress compression and pulling and pressing combined action; the second determining unit is used for determining a relation model of radial stress and salt paste layer ground stress at an infinite distance from the shaft by using a stress superposition principle on the assumption that deformation is small under an independent stress state around the shaft.
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