Shale oil well pressure calculation model construction method based on replacement condition

Abstract

The invention discloses a shale oil well pressure calculation model construction method based on a replacement condition. The method comprises the following steps that 1, a calculation formula of an annular pressure calculation model is determined; step 2, determining a calculation formula of the temperature model; 3, determining a calculation formula of the density model; step 4, determining a calculation formula of the pressure consumption model; and 5, solving the annulus pressure calculation model, the temperature model, the density model and the pressure consumption model. According to the shale oil well pressure calculation model construction method based on the replacement condition, the annulus pressure distribution in the shale oil well under the replacement condition and the influence of the annulus pressure distribution on the productivity and the oil well pressure can be more accurately predicted, and the annulus pressure of the shale oil well can be accurately calculated.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil engineering safety, and particularly relates to a method for constructing a shale oil well pressure calculation model based on displacement conditions. Background Art

[0002] Shale oil refers to the petroleum resources contained in shale formations mainly composed of shale, including petroleum in shale pores and fractures, as well as petroleum resources in tight carbonate rocks or clastic rock adjacent layers and interlayers in shale formations. Producing light oil products from shale oil is one of the methods with the lowest cost in the production of synthetic petroleum to obtain qualified liquid fuels.

[0003] With the increase in energy demand and the development of technology, shale oil has become a remarkable focus in the current energy field. However, during the drilling and production process of shale oil, a displacement phenomenon often occurs between the drilling fluid and the formation fluid. The displacement phenomenon refers to the situation where when the drilling fluid circulates in the annulus, the drilling fluid enters the formation while the formation fluid (oil, gas, brine, etc.) gradually invades the annulus and circulates together with the drilling fluid in the wellbore.

[0004] It should be noted that during the displacement process, a dynamic fluid exchange phenomenon will occur between the drilling fluid in the wellbore and the formation fluid around the well. This displacement phenomenon will cause changes in the composition of the fluid in the annulus, resulting in pressure changes in the annulus, and ultimately affecting the oil and gas migration and productivity in the oil well. At present, there is less research on the displacement phenomenon in horizontal well drilling, and there are still great deficiencies in understanding its occurrence mechanism and the influence law of parameters.

[0005] The accurate calculation of wellbore pressure is crucial for the safe and efficient exploitation of shale oil. Wellbore pressure is a key parameter for evaluating the well stability, predicting oil and gas productivity, and conducting effective production management. In tight reservoirs such as shale oil, pressure changes have a significant impact on productivity and recovery rate. Accurate wellbore pressure calculation can provide key information to help determine appropriate oil production strategies and optimize well spacing. In addition, understanding the changes in wellbore pressure also helps to predict processes such as fracture propagation, oil and gas flow, and water flooding, thereby guiding subsequent stimulation and optimization measures to achieve efficient and sustainable shale oil development.

[0006] During the drilling process of shale oil exploitation, the displacement phenomenon often occurs, which refers to the fluid exchange phenomenon between the oil-based mud and the formation fluid. This process has an important impact on the annulus pressure distribution in the wellbore. The existing annulus pressure calculation models cannot predict the annulus pressure distribution based on displacement conditions. To solve this problem, the present invention proposes a new wellbore pressure calculation model. Summary of the Invention

[0007] To solve the above problems, the present disclosure provides a method for constructing a shale oil well pressure calculation model under displacement conditions to accurately calculate the annulus pressure of shale oil wells during the drilling and production process of shale oil.

[0008] A method for constructing a shale oil well pressure calculation model under displacement conditions of the present invention includes the following steps:

[0009] Step 1: Determine the calculation formula of the annulus pressure calculation model;

[0010] Step 2: Determine the calculation formula of the temperature model;

[0011] Step 3: Determine the calculation formula of the density model;

[0012] Step 4: Determine the calculation formula of the pressure loss model;

[0013] Step 5: Solve the annulus pressure calculation model, temperature model, density model, and pressure loss model.

[0014] In specific implementation, in step 1, the premise of determining the annulus pressure calculation formula is to assume that the annulus flow of variable pressure gradient drilling under normal circulation conditions is a steady flow, and at the same time consider the difference in the density of the annulus fluid above and below the displacement point.

[0015] In specific implementation, in step 1, the annulus pressure calculation formula is shown in formula (1);

[0016]

[0017] In formula (1), ρ a1 is the density of the mixed fluid in the annulus and the formation, with the unit of g / cm 3 ; θ is the angle between the wellbore direction and the horizontal direction, with the unit of °; P wh is the wellhead back pressure, with the unit of Pa; ΔP a is the frictional pressure drop of the mixed drilling fluid density per unit length, with the unit of Pa / m; h1 is the height of the displacement point from the bottom of the well, with the unit of m; h is the distance from any height to the bottom of the well, with the unit of m; H is the total well depth, with the unit of m; ρ a1 is the density of the mixed fluid, with the unit of g / cm 3 ; ρ a is the density of the annulus drilling fluid mixture, with the unit of g / cm 3 ; ΔP a1 is the frictional pressure drop of the annulus drilling fluid density per unit length, with the unit of Pa / m; g is the acceleration due to gravity, with the unit of m / s 2 .

[0018] In specific implementation, in step 2, the calculation formula of the temperature model is shown in formula (2);

[0019]

[0020] In formula (2), the calculation of parameters C1 to C7 is shown in formula (3);

[0021]

[0022] In formulas (2) and (3), c a1 is the specific heat capacity of the mixed micro - element flowing out of the annulus, with the unit of J / (kg·℃); ρ a1 is the density of the mixed fluid after displacement in the annulus, with the unit of kg / m 3 ; S a is the flow area of the fluid in the annulus, with the unit of m 2 ; c a is the specific heat capacity of the fluid flowing into the annulus, with the unit of J / (kg·℃); q ma is the mass flow rate of the fluid flowing into the annulus, with the unit of kg / s; q maL is the mass flow rate of the fluid flowing out of the annulus after displacement in the annulus, with the unit of kg / s; R p is the outer diameter of the drill pipe, with the unit of m; H p is the wall thickness of the drill pipe, m; λ p is the thermal conductivity of the drill pipe, with the unit of W / (m·℃); R Tf is the outer diameter of the cylinder at the geothermal temperature position, with the unit of m; λ f is the thermal conductivity of the wellbore wall, with the unit of W / (m·℃); D Tf is the outer diameter of the cylinder at the geothermal temperature position, with the unit of m; c f is the specific heat capacity of the formation fluid flowing into the annulus, with the unit of J / (kg·℃); q mf is the mass flow rate of the formation fluid flowing into the annulus fluid, with the unit of kg / s; Δq maL is the mass flow rate of the annulus fluid flowing into the formation fluid, with the unit of kg / s; T a(L+△L) , T aL are the temperatures of the fluid flowing into and out of the micro - element in the annulus respectively, with the unit of ℃; T f(L+△L) is the original formation temperature at depth L + ΔL, with the unit of ℃; T pL is the temperature of the drill pipe at depth L, with the unit of ℃. ΔL is the length of the micro - element, with the unit of m; L is the position depth of any micro - element, with the unit of m; △t is the time step, s; i represents the i - th moment.

[0023] In specific implementation, in step 3, the calculation formula of the density model is shown in formula (4);

[0024]

[0025] In formula (4), ρ (P,T) is the density of the drilling fluid at a pressure of P MPa and a temperature of T °C, with the unit of g / cm 3 ; ρ 0(P,T) is the density of the drilling fluid at a pressure of P0 MPa and a temperature of T0 °C, with the unit of g / cm 3 ; a, b, and c are all model coefficients, with dimensionless units.

[0026] During specific implementation, the density of the mixed fluid also needs to be calculated in step 3; the density of the mixed fluid includes the density of the annulus drilling fluid mixture ρ a and the density of the mixture of the annulus and formation fluids ρ a1 .

[0027] During specific implementation, the calculation formula for the density of the annulus drilling fluid mixture ρ a is shown in formula (5);

[0028]

[0029] In formula (5), ρ a is the density of the annulus drilling fluid mixture, with the unit of g / cm 3 ; ρ p is the density of the drilling fluid inside the drill pipe, with the unit of kg / m 3 ; Q1 is the displacement of the drilling fluid per unit time, with the unit of m 3 / s; ρ c is the density of the cuttings, with the unit of kg / m 3 ; Q c is the displacement of the cuttings, with the unit of m / s.

[0030] During specific implementation, the calculation formula for the density of the formation mixed fluid ρ a1 is shown in formula (6);

[0031]

[0032] In formula (6), ρ a1 is the density of the mixture of the annulus and formation fluids, with the unit of g / cm 3 ; ρ p is the density of the drilling fluid inside the drill pipe, with the unit of kg / m 3 ; Q1 is the displacement of the drilling fluid per unit time, with the unit of m 3 / s; ρ c is the density of the cuttings, with the unit of kg / m3; Q c is the displacement of the cuttings, with the unit of m / s; ΔQ1 is the displacement of the mixed fluid flowing into the formation in the annulus per unit time, with the unit of m 3 / s; ρ f is the density of the mixed fluid in the formation, with the unit of kg / m3 ; Q f is the displacement of formation fluid per unit time, with the unit of m / s.

[0033] During specific implementation, the calculation formula of the pressure loss model is shown in Formula (7);

[0034]

[0035] In Formula (7), f is the Fanning friction factor, dimensionless; ρ is the density of the annulus fluid, with the unit of g / cm 3 ; v is the average fluid velocity, m 3 / s; L is the position depth of any infinitesimal element, with the unit of m; D is the diameter of the pipe, with the unit of m.

[0036] The present invention also provides an electronic device, including at least one processor and a memory communicatively connected to the at least one processor; wherein, the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the method for constructing a shale oil well pressure calculation model based on replacement conditions.

[0037] The present invention also provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the method for constructing a shale oil well pressure calculation model based on replacement conditions is implemented.

[0038] Compared with the prior art, the present disclosure has the following advantages:

[0039] The method for constructing a shale oil well pressure calculation model based on replacement conditions of the present invention includes the following steps: Step 1: Determine the calculation formula of the annulus pressure calculation model; Step 2: Determine the calculation formula of the temperature model; Step 3: Determine the calculation formula of the density model; Step 4: Determine the calculation formula of the pressure loss model; Step 5: Solve the annulus pressure calculation model, temperature model, density model and pressure loss model.

[0040] The method for constructing a shale oil well pressure calculation model based on replacement conditions of the present invention, based on the change of wellbore pressure caused by the interchange of drilling fluid and formation fluid under the special working conditions of replacement conditions, comprehensively considers the influence of various factors on the wellbore pressure during the fluid replacement phenomenon in the drilling process, so as to accurately predict the annulus pressure distribution. The invention of this new model can provide a new method for the pressure calculation of shale oil wells, fill the research gap of the existing annulus pressure calculation model under replacement conditions, and provide practical support for the efficient development and utilization of shale oil.

[0041] The method for constructing a shale oil well pressure calculation model based on displacement conditions according to the present invention comprehensively considers the movement of shale oil in rock pores and the dynamic process of fluid displacement, and will be able to more accurately predict the annulus pressure distribution in the shale oil well under displacement conditions and its influence on productivity and well pressure, and can accurately calculate the annulus pressure of the shale oil well. This research will be of great significance for optimizing the exploitation strategy and production management of shale oil wells, and providing scientific guidance for the efficient development and utilization of energy resources.

[0042] The method for constructing a shale oil well pressure calculation model based on displacement conditions according to the present invention can more accurately predict the annulus pressure distribution in the shale oil well under displacement conditions and its influence on productivity and well pressure, and accurately calculate the annulus pressure of the shale oil well.

[0043] Other features and advantages of the present invention will be described in the following specification, and, in part, will become apparent from the specification, or will be understood by practicing the present invention. The objectives and other advantages of the present invention can be achieved and obtained by the structures pointed out in the specification, claims, and drawings. Brief Description of the Drawings

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0045] Figure 1 Shows a schematic diagram of ground - wellbore - formation fluid flow;

[0046] Figure 2 Is a schematic flow diagram of the temperature - pressure coupling solution of the present invention;

[0047] Figure 3 Schematic diagram of the influence of different displacement point positions on the wellbore pressure in the present invention. Detailed Description of the Invention

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0049] Such as Figures 1-3, A method for constructing a shale oil well pressure calculation model based on replacement conditions according to the present invention includes the following steps:

[0050] Step 1: Determine the calculation formula of the annulus pressure calculation model;

[0051] Step 2: Determine the calculation formula of the temperature model;

[0052] Step 3: Determine the calculation formula of the density model;

[0053] Step 4: Determine the calculation formula of the pressure loss model;

[0054] Step 5: Solve the annulus pressure calculation model, temperature model, density model and pressure loss model.

[0055] The method for constructing a shale oil well pressure calculation model based on replacement conditions according to the present invention comprehensively considers the steady-state flow under normal circulation conditions and the difference in the annulus fluid density at the upper and lower parts of the replacement point to determine the annulus pressure calculation formula. Since the high-temperature environment will significantly change the physical properties of the fluid, such as viscosity and expansion effect, which will have an important impact on the flow characteristics of the fluid. Therefore, when calculating the annulus pressure in high-temperature and high-pressure wells, the influence of the temperature model, density model and pressure loss model must be considered, so the calculation formulas of the three models, namely the temperature model, density model and pressure loss model, are determined.

[0056] During specific implementation, in the said Step 1, the premise for determining the annulus pressure calculation formula is to assume that the annulus flow of variable pressure gradient drilling under normal circulation conditions is a steady flow, and at the same time consider the difference in the annulus fluid density at the upper and lower parts of the replacement point.

[0057] During specific implementation, in the said Step 1, the annulus pressure calculation formula is shown in Formula (1);

[0058]

[0059] In Formula (1), ρ a1 is the density of the annulus and formation mixed fluid, with the unit of g / cm 3 ; θ is the angle between the wellbore direction and the horizontal direction, with the unit of °; P wh is the wellhead back pressure, with the unit of Pa; ΔP a is the frictional pressure drop of the mixed drilling fluid density per unit length, with the unit of Pa / m; h1 is the height of the replacement point from the bottom of the well, with the unit of m; h is the distance from any height to the bottom of the well, with the unit of m; H is the total well depth, with the unit of m; ρ a1 is the density of the mixed fluid, with the unit of g / cm 3 ; ρ a is the density of the annulus drilling fluid mixture, with the unit of g / cm 3 ; ΔP a1is the frictional pressure drop of the annulus drilling fluid density per unit length, with the unit of Pa / m; g is the acceleration due to gravity, with the unit of m / s 2 .

[0060] In the process of establishing the above annulus pressure calculation formula, the premise is to assume that under normal circulation conditions, the annulus flow in variable pressure gradient drilling is a steady flow, and the difference in annulus fluid density between the upper and lower parts of the displacement point is considered. First, the steady flow under normal circulation conditions is considered. In this case, it is assumed that the annulus fluid in the wellbore satisfies a constant pressure gradient and the flow process is stable. This assumption is to establish the basic framework of the annulus pressure calculation model of the present invention. Second, the difference in annulus fluid density between the upper and lower parts of the displacement point is concerned. During the displacement process, the drilling fluid in the wellbore and the formation fluid are displaced, and the annulus fluid density of the upper and lower parts will be different. Considering this factor, it is recognized that the pressure distribution of annulus fluids with different densities will change near the displacement point. Therefore, the annulus pressure calculation formula can comprehensively consider the steady flow under normal circulation conditions and the difference in annulus fluid density between the upper and lower parts of the displacement point. Through this annulus pressure calculation formula, the pressure distribution of the shale oil wellbore under displacement conditions can be predicted more accurately.

[0061] In specific implementation, in step 2, the calculation formula of the temperature model is shown in formula (2);

[0062]

[0063] In formula (2), the calculation of parameters C1 to C7 is shown in formula (3);

[0064]

[0065] In formula (2) and formula (3), c a1 is the specific heat capacity of the mixed microelement flowing out of the annulus in the annulus, with the unit of J / (kg·℃); ρ a1 is the density of the mixed fluid after displacement in the annulus, with the unit of kg / m 3 ; S a is the area of fluid flow in the annulus, with the unit of m 2 ; c a is the specific heat capacity of the fluid flowing into the annulus, with the unit of J / (kg·℃); q ma is the mass flow rate of the fluid flowing into the annulus, with the unit of kg / s; q maL is the mass flow rate of the fluid flowing out of the annulus after displacement in the annulus, with the unit of kg / s; R p is the outer diameter of the drill pipe, with the unit of m; H p is the wall thickness of the drill pipe, m; λ p is the thermal conductivity of the drill pipe, with the unit of W / (m·℃); R Tfis the outer diameter of the cylinder at the geothermal temperature position, in m; λ f is the thermal conductivity of the wellbore, in W / (m·°C); D Tf is the outer diameter of the cylinder at the geothermal temperature position, in m; c f is the specific heat capacity of the formation fluid flowing into the annulus, in J / (kg·°C); q mf is the mass flow rate of the formation fluid flowing into the annulus fluid, in kg / s; Δq maL is the mass flow rate of the annulus fluid flowing into the formation fluid, in kg / s; T a(L+△L) ,T aL are the fluid temperatures of the micro - element flowing into and out of the annulus respectively, in °C; T f(L+△L) is the original formation temperature at depth L + ΔL, in °C; T pL is the drill pipe temperature at depth L, in °C. ΔL is the length of the micro - element, in m; L is the position depth of any micro - element, in m; △t is the time step, in s; i represents the i - th moment.

[0066] The use of the temperature model is crucial for estimating the temperature distribution of the fluid. A high - temperature environment will cause non - uniform distribution of the fluid temperature. Therefore, an accurate temperature model can provide information on how the fluid temperature changes with well depth and the wellbore wall, providing a basis for annulus pressure calculation.

[0067] During specific implementation, in step 3, the calculation formula of the density model is shown in formula (4);

[0068]

[0069] In formula (4), ρ (P,T) is the density of the drilling fluid at pressure P in MPa and temperature T in °C, in g / cm 3 ; ρ 0(P,T) is the density of the drilling fluid at pressure P0 in MPa and temperature T0 in °C, in g / cm 3 ; a, b, and c are all model coefficients, dimensionless units.

[0070] In high - temperature and high - pressure wells, the density of the fluid will change with temperature and pressure. Therefore, an accurate density model can help us calculate the fluid density at different temperatures and pressures, which in turn affects the calculation result of the annulus pressure.

[0071] During specific implementation, in step 3, it is also necessary to calculate the density of the mixed fluid; the density of the mixed fluid includes the density of the annulus drilling fluid mixture ρ a and the density of the annulus - formation mixed fluid ρ a1 .

[0072] During the drilling process, a small amount of cuttings may enter the annulus, and when the annulus is replaced with the formation, the thermodynamic properties of the mixed fluid in a single annulus environment will change.

[0073] During specific implementation, the mixed density ρ of the annulus drilling fluid a The calculation formula is shown in Formula (5);

[0074]

[0075] In Formula (5), ρ a is the mixed density of the annulus drilling fluid, with the unit of g / cm 3 ; ρ p is the density of the drilling fluid in the drill pipe, with the unit of kg / m 3 ; Q1 is the displacement of the drilling fluid per unit time, with the unit of m 3 / s; ρ c is the density of the cuttings, with the unit of kg / m 3 ; Q c is the displacement of the cuttings, with the unit of m / s.

[0076] During specific implementation, the density ρ of the formation mixed fluid a1 The calculation formula is shown in Formula (6);

[0077]

[0078] In Formula (6), ρ a1 is the density of the mixed fluid in the annulus and the formation, with the unit of g / cm 3 ; ρ p is the density of the drilling fluid in the drill pipe, with the unit of kg / m 3 ; Q1 is the displacement of the drilling fluid per unit time, with the unit of m 3 / s; ρ c is the density of the cuttings, with the unit of kg / m 3 ; Q c is the displacement of the cuttings, with the unit of m / s; ΔQ1 is the displacement of the mixed fluid in the annulus flowing into the formation per unit time, with the unit of m 3 / s; ρ f is the density of the mixed fluid in the formation, with the unit of kg / m 3 ; Q f is the displacement of the formation fluid per unit time, with the unit of m / s.

[0079] During specific implementation, the calculation formula of the pressure loss model is shown in Formula (7);

[0080]

[0081] In formula (7), f is the Fanning friction factor, dimensionless; ρ is the density of the annulus fluid, with the unit of g / cm 3 ; v is the average fluid velocity, in m 3 / s; L is the position depth of any infinitesimal element, with the unit of m; D is the diameter of the pipe, with the unit of m.

[0082] The consideration of the pressure loss model is to accurately estimate the pressure loss during the fluid flow in the wellbore. Under high-temperature and high-pressure environments, the friction, inertia of the fluid, and the changes in well depth and well diameter will cause the reduction of fluid pressure. Therefore, it is necessary to consider the influence of these factors on the annulus pressure and use an appropriate pressure loss model for calculation.

[0083] The present invention also provides an electronic device, including at least one processor and a memory communicatively connected to the at least one processor; wherein, the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the method for constructing a shale oil well pressure calculation model based on replacement conditions.

[0084] The present invention also provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the method for constructing a shale oil well pressure calculation model based on replacement conditions is implemented.

[0085] The solution of the model under the condition of temperature-pressure coupling is important for understanding and predicting complex thermodynamic processes. Under high-temperature and high-pressure environments, the temperature and pressure of the fluid interact with each other, resulting in changes in physical properties, such as density, viscosity, and heat conduction performance, etc. This coupling effect has a significant impact on fluid flow, heat transfer, and mass transfer processes. Therefore, establishing and solving the temperature-pressure coupling model can help us more accurately describe and predict these complex thermodynamic phenomena.

[0086] When solving the annulus temperature and pressure model for variable pressure gradient drilling, the double-loop iteration method is adopted. This method first conducts the convergence calculation of pressure and then conducts the convergence calculation of temperature. The solution process of the double-loop iteration method is as follows:

[0087] (1) First, according to the initial conditions and boundary conditions, iterative calculations are carried out using the pressure equation to obtain the pressure distribution at each point in the annulus. During this process, considering the influence of fluid flow and wellbore geometry, the convergence of pressure is achieved through iterative solution.

[0088] (2) Once the convergent solution of the pressure distribution is obtained, the convergence calculation of temperature is then carried out. Using the temperature equation and the known pressure distribution, the temperature distribution at each point in the annulus is obtained through iterative solution. In this step, factors such as fluid heat conduction, heat transfer, and environmental heat exchange are considered to achieve the convergence of temperature.

[0089] By using the double-loop iteration method, we can adjust the pressure and temperature iteratively during the solution process until the convergence criterion is met. This method fully considers the mutual influence between pressure and temperature and can accurately calculate the temperature and pressure distributions in the annulus of variable-pressure-gradient drilling.

[0090] By using the double-loop iteration method to solve the model, we can better understand and predict the thermodynamic behavior of the annulus in variable-pressure-gradient drilling. This solution method can provide accurate temperature and pressure distributions, providing a reliable basis for operations and equipment design during the drilling process. The specific solution steps are as Figure 2 shown.

[0091] In specific implementation, the new wellbore pressure calculation model based on displacement conditions established according to the present invention is applied to the actual drilling data of Well X in a certain oilfield in Xinjiang, and the analysis calculation results are as Figure 3 shown.

[0092] When the displacement occurs at the bottom of the well, there is no obvious inflection point in the annulus pressure distribution curve. When the displacement point is located in the upper open hole section, an inflection point appears in the curve, and the position of the inflection point is consistent with the position of the displacement point. From this result, we conclude that: at the moment of displacement inside the wellbore, pressure fluctuations are likely to occur at this point. Such pressure fluctuations may have a certain impact on the pressure distribution and stability inside the wellbore. This conclusion not only provides an important clue for us to deeply understand the pressure behavior inside the wellbore, but also provides a scientific basis for optimizing pressure management during drilling operations and production processes. Considering comprehensively, this research not only has important guiding significance for oilfield development practice, but also expands our understanding of wellbore pressure behavior in the field of oilfield engineering.

[0093] By comprehensively applying the temperature model, density model, and pressure loss model, we can more accurately calculate the annulus pressure in high-temperature and high-pressure wells. Such calculation results can provide a reliable basis for downhole operations and equipment design, thus ensuring the safety and effectiveness of the drilling process.

[0094] The method for constructing the pressure calculation model of shale oil wells based on displacement conditions of the present invention has the following characteristics.

[0095] 1. Improve calculation accuracy: Traditional shale oil well pressure calculation models often ignore the influence of the displacement between drilling fluid and formation fluid, resulting in inaccurate pressure calculation results. The model of the present invention can more accurately predict the change of wellbore pressure by considering the displacement process, improving the calculation accuracy.

[0096] 2. Improve production management decisions: Accurate wellbore pressure calculation results can provide an important basis for the production management of shale oil extraction. The pressure change law obtained by calculating with the model of the present invention can help formulate reasonable production strategies, improve production capacity and recovery rate, thereby improving the effect of production management decisions.

[0097] 3. Improve resource utilization efficiency: The model of the present invention can better reveal the dynamic pressure change law of shale oil wells and help optimize resource utilization. By reasonably predicting the wellbore pressure, the resource utilization efficiency can be improved and the extraction cost can be reduced.

[0098] 4. Save costs: Correctly estimating the annulus pressure distribution can avoid unnecessary trial and error and adjustments, thus saving time and costs during the extraction process. Reasonable extraction strategies and operations can reduce production costs and improve economic benefits.

[0099] The present invention provides a method for constructing a pressure calculation model for shale oil wells with downhole displacement of oil-based drilling fluid considering the influence of temperature and pressure, aiming to solve the problem of low calculation accuracy of traditional models when considering the displacement effect. This new model includes the following key steps: First, a calculation model for the wellbore pressure of shale oil wells under displacement conditions is established, and an advanced numerical solution method is used for solving. Second, by introducing an auxiliary model, the key parameters in the new pressure calculation model are effectively determined, further improving the accuracy and reliability of the model. The present invention fully considers the influence of displacement conditions on the wellbore pressure of shale oil wells and proposes a brand-new pressure calculation model. This invention can provide an important reference basis for the production and management of shale oil wells.

[0100] Generally speaking, the method for constructing a pressure calculation model for shale oil wells based on displacement conditions of the present invention can improve calculation accuracy, improve production management decisions, guide production increase and optimization measures, and improve resource utilization efficiency, which will promote the progress of shale oil extraction technology and facilitate the effective development and utilization of shale oil resources.

[0101] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0102] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment contains only one independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for constructing a pressure calculation model of a shale oil well under replacement conditions, characterized in that The method includes the following steps: Step 1: Establish the calculation formula of the annulus pressure calculation model; Step 2: Establish the calculation formula of the temperature model; Step 3: Establish the calculation formula of the density model; Step 4: Establish the calculation formula of the pressure loss model; Step 5: Solve the annulus pressure calculation model, temperature model, density model and pressure loss model.

2. The method for constructing a shale oil well pressure calculation model based on replacement conditions according to claim 1, wherein In the said Step 1, the premise of establishing the annulus pressure calculation formula is to assume that the annulus flow in variable pressure gradient drilling is a steady flow under normal circulation conditions, and at the same time consider the density difference of the annulus fluid above and below the displacement point.

3. The method for constructing a shale oil well pressure calculation model based on replacement conditions according to claim 2, wherein, In the said Step 1, the annulus pressure calculation formula is shown in Formula (1); In Formula (1), ρa1 is the density of the mixed fluid in the annulus and formation, θ is the angle between the wellbore direction and the horizontal direction, Pwh is the wellhead back pressure, ΔPa is the frictional pressure drop of the mixed drilling fluid density per unit length, h1 is the height of the displacement point from the bottom of the well, h is the distance from any height to the bottom of the well, H is the total well depth, ρa1 is the density of the mixed fluid, ρa is the density of the annulus drilling fluid mixture, ΔPa1 is the frictional pressure drop of the annulus drilling fluid density per unit length, and g is the acceleration due to gravity.

4. The method for constructing a shale oil well pressure calculation model based on replacement conditions according to claim 1, characterized in that, In the said Step 2, the calculation formula of the temperature model is shown in Formula (2); In Formula (2), the calculation of parameters C1 to C7 is shown in Formula (3); In Formulas (2) and (3), c a1 is the specific heat capacity of the mixed element flowing out of the annulus in the annulus, ρ a1 is the density of the mixed fluid after displacement in the annulus, S a is the flow area of the fluid in the annulus, c a is the specific heat capacity of the fluid flowing into the annulus, q ma is the mass flow rate of the fluid flowing into the annulus, q maL is the mass flow rate of the fluid flowing out of the annulus after displacement in the annulus, R p is the outer diameter of the drill pipe, and is the wall thickness of the drill pipe, m; λ p is the thermal conductivity of the drill pipe, R Tf is the outer diameter of the cylinder at the geothermal temperature position, λ f is the thermal conductivity of the wellbore wall, D Tf is the outer diameter of the cylinder at the geothermal temperature position, c f is the specific heat capacity of the formation fluid flowing into the annulus, q mf is the mass flow rate of the formation fluid flowing into the annulus fluid, Δq maL is the mass flow rate of the annulus fluid flowing into the formation fluid, T a(L+△L) , T aL are the fluid temperatures of the micro-elements flowing into and out of the annulus respectively, T f(L+△L) is the original formation temperature at depth L + ΔL, T pL is the drill pipe temperature at depth L, ΔL is the length of the micro-element, L is the position depth of any micro-element, △t is the time step, s; i represents the i-th moment.

5. The method for constructing a shale oil well pressure calculation model based on replacement conditions according to claim 1, characterized in that In the said Step 3, the calculation formula of the density model is shown in Formula (4); In formula (4), ρ (P,T) is the density of the drilling fluid at pressure P MPa and temperature T °C, and ρ 0(P,T) is the density of the drilling fluid at pressure P0 MPa and temperature T0 °C. a, b, and c are all model coefficients, with dimensionless units.

6. The method for constructing a shale oil well pressure calculation model based on replacement conditions according to claim 5, wherein In step 3, it is also necessary to calculate the density of the mixed fluid; the density of the mixed fluid includes the density of the annulus drilling fluid mixture ρ a and the density of the mixed fluid of the annulus and the formation ρ a1 .

7. The method for constructing a shale oil well pressure calculation model based on replacement conditions according to claim 6, wherein The mixing density ρ of the annulus drilling fluid a is calculated according to Equation (5); In formula (5), ρ a is the mixed density of the annulus drilling fluid, ρ p is the density of the drilling fluid inside the drill pipe, Q1 is the displacement of the drilling fluid per unit time, ρ c is the density of the cuttings, Q c is the displacement of the cuttings.

8. The method for constructing a shale oil well pressure calculation model based on replacement conditions according to claim 6, characterized in that, The density ρ of the formation mixed fluid a1 The calculation formula is shown in Formula (6); In formula (6), ρ a1 is the density of the annulus and formation mixed fluid, ρ p is the density of the drilling fluid in the drill pipe, Q1 is the displacement of the drilling fluid per unit time, ρ c is the density of the cuttings, Q c is the displacement of the cuttings, ΔQ1 is the displacement of the mixed fluid in the annulus flowing into the formation per unit time, ρ f is the density of the mixed fluid in the formation, Q f is the displacement of the formation fluid per unit time.

9. The method for constructing a shale oil well pressure calculation model based on replacement conditions according to claim 1, wherein The calculation formula of the pressure loss model is shown in Formula (7); In Formula (7), f is the Fanning friction factor, dimensionless; ρ is the density of the annulus fluid, v is the average fluid velocity, L is the position depth of any microelement, and D is the diameter of the pipe.

10. An electronic device, characterized in that, It includes at least one processor and a memory communicatively connected to the at least one processor; wherein, the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the method for constructing a shale oil well pressure calculation model based on displacement conditions as described in any one of Claims 1 to 9.

11. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the method for constructing a shale oil well pressure calculation model based on displacement conditions as described in any one of Claims 1 to 9.

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