Method for predicting integrity of hydrate exploitation well in sea area

Abstract

The invention relates to a method for predicting the integrity of a hydrate mining well in a sea area. The method comprises the following steps: analyzing logging data and a coring sample; establishing a full-size geomechanical model based on the logging data and the coring sample; reservoir deformation caused by mining is quantitatively calculated; the displacement and stress of the whole well section of the mining well are calculated; based on the displacement and stress analysis of the whole well section of the mining well, a risk area of shaft integrity is speculated; designing a solution for reducing the risk; by calculating the displacement and stress of the whole well section of the mining well, the integrity risk of the mining well caused by stratum settlement is effectively predicted, the integrity risk area of the shaft can be predicted in the making stage of a sea area hydrate development scheme, corresponding adjustment is conducted in well track design, and the development efficiency is improved. Therefore, the wellbore integrity risk of a sea area hydrate mining well is reduced, and the safety and reliability of the mining well are improved.

Description

Technical Field

[0001] This invention relates to the field of marine hydrate extraction technology, and in particular to a method for predicting the integrity of marine hydrate extraction wells. Background Technology

[0002] Currently, the depressurization method for extracting natural gas hydrates in offshore areas can lead to reservoir deformation and subsidence of the overlying layer. This reservoir deformation is a contributing factor to wellbore integrity risks in hydrate extraction wells.

[0003] Currently, offshore natural gas hydrate extraction is in the experimental stage and has a short extraction time. Further prediction and evaluation of the risks that long-term extraction may pose are needed. Existing research methods and industry standards do not consider the weak cementation properties of shallow seafloor silty mudstone, and predictions of reservoir deformation caused by depressurization are limited to the wellbore area, failing to predict the risk to the integrity of shallow seafloor wellbores due to overburden subsidence.

[0004] However, because traditional oil and gas wells are located in deep reservoirs with high mechanical strength and are injection-production wells, the subsidence caused by the pressure reduction is not significant. But hydrate reservoirs are located in shallow seabed layers with low mechanical strength, and pressure reduction extraction may cause large-scale formation subsidence, reducing safety and reliability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for predicting the integrity of marine hydrate extraction wells. Its advantages include the ability to effectively predict the integrity risks of extraction wells caused by formation subsidence, and the ability to predict wellbore integrity risk areas during the formulation of marine hydrate development plans, thereby increasing the safety and reliability of extraction wells.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution: a method for predicting the integrity of marine hydrate extraction wells, comprising the following steps:

[0007] Analyze well logging data and coring samples;

[0008] Based on the well logging data and the core samples, a full-size geomechanical model was established.

[0009] Quantitatively calculate the reservoir deformation caused by mining;

[0010] Calculate the displacement and stress of the entire well section;

[0011] Based on the displacement and stress analysis of the entire well section, the risk areas for wellbore integrity are inferred;

[0012] Design solutions to mitigate risks.

[0013] Preferably, the method for predicting the integrity of marine hydrate extraction wells provided by the present invention includes well logging data including lithology, clay content, gas-water-hydrate three-phase saturation, porosity, and permeability.

[0014] Preferably, the method for predicting the integrity of marine hydrate extraction wells provided by the present invention includes the distribution of elastic modulus, Poisson's ratio, cohesion, and friction angle parameters along depth in the core sample.

[0015] Preferably, in the method for predicting the integrity of marine hydrate extraction wells provided by the present invention, the full-size geomechanical model is an elastic model or an elastoplastic model.

[0016] Preferably, the method for predicting the integrity of marine hydrate extraction wells provided by the present invention includes the quantitative calculation of reservoir deformation caused by extraction, which includes: based on the full-size geomechanical model and the bottom hole pressure during the extraction stage, quantitatively calculating the stress field and displacement field of the reservoir and overlying layer caused by the reduction of bottom hole pressure.

[0017] Preferably, the method for predicting the integrity of marine hydrate extraction wells provided by the present invention involves radial seepage of fluid from reservoir pores into the wellbore during depressurization extraction, wherein the steady-state seepage in a circular formation is solved as follows:

[0018]

[0019] In the formula, r w Let R be the radius of the well, and p be the range of influence of the seepage from the well. w To extract the bottom hole pressure, p e Let be the initial pore pressure of the reservoir, r be the distance between any position and the wellbore, and p(r) be the pore pressure at point r.

[0020] Preferably, in the method for predicting the integrity of marine hydrate extraction wells provided by the present invention, the formation strain is:

[0021]

[0022] In the formula, ε is the strain of the formation, E is the elastic modulus, and v is Poisson's ratio.

[0023] Preferably, the method for predicting the integrity of marine hydrate production wells provided by the present invention includes calculating the displacement and stress of the entire production well section, comprising: using the displacement and stress fields of the reservoir and the overlying cover as boundary conditions, calculating the stress and displacement of the entire production well section under the action of the stress and displacement fields of the reservoir and the overlying cover, wherein the stress analysis includes one or more of the following: axial stress, bending stress, or shear stress of the casing, cement sheath, and screen.

[0024] Preferably, the method for predicting the integrity of marine hydrate production wells provided by the present invention includes the risk areas of wellbore integrity, which include areas where the wellbore structure is at risk of wellbore integrity under the stress and strain of the reservoir and the overlying strata, as well as potential risk areas under the action of fault slip boundaries.

[0025] Preferably, the method for predicting the integrity of marine hydrate extraction wells provided by the present invention includes a risk mitigation solution comprising: adjusting the build-up point, build-up section length, well type structure, and well spacing parameters of the hydrate extraction well to ensure that the wellbore structure avoids areas where wellbore integrity risks occur.

[0026] In summary, the beneficial technical effects of this invention are as follows: The method for predicting the integrity of marine hydrate extraction wells provided in this application includes the following steps: analyzing logging data and core samples; establishing a full-scale geomechanical model based on the logging data and core samples; quantitatively calculating the reservoir deformation caused by extraction; calculating the displacement and stress of the entire well section; inferring the risk area of ​​wellbore integrity based on the displacement and stress analysis of the entire well section; designing solutions to mitigate the risk; by calculating the displacement and stress of the entire well section, the integrity risk of extraction wells caused by formation subsidence can be effectively predicted. This allows for the prediction of wellbore integrity risk areas during the formulation of marine hydrate development plans and corresponding adjustments in wellbore trajectory design, thereby reducing the wellbore integrity risk of marine hydrate extraction wells and increasing the safety and reliability of extraction wells. Attached Figure Description

[0027] Figure 1 This is a flowchart of a method for predicting the integrity of marine hydrate extraction wells provided in an embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of the reservoir and wellbore structure of a marine hydrate extraction well in the method for predicting the integrity of marine hydrate extraction wells provided in this embodiment of the invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the accompanying drawings.

[0030] Reference Figure 1 and Figure 2 The present invention discloses a method for predicting the integrity of marine hydrate extraction wells, comprising the following steps:

[0031] S101, Analyze logging data and core samples.

[0032] Specifically, well logging data refers to geological information obtained from the processing and qualitative interpretation of well logging data. Well logging data includes lithology, clay content, three-phase saturation of gas-water-hydrate, porosity, and permeability.

[0033] In this embodiment, the core sample is the core mechanical parameters measured by the core laboratory test. The core sample includes the distribution of elastic modulus, Poisson's ratio, cohesion, and friction angle parameters along the depth.

[0034] S102. Based on well logging data and core samples, establish a full-scale geomechanical model.

[0035] Among them, a full-scale geomechanical model at the engineering scale is established based on the mechanical parameters obtained from well logging data and core sample analysis before mining.

[0036] Specifically, gravity and seawater pressure are applied through numerical calculations. The required parameters are elastic modulus, Poisson's ratio, porosity, permeability, and hydrate saturation. Since the testing of core samples is limited by the core sampling location, only the strata mechanical properties at a certain depth can be obtained. The evolution of each parameter with depth is inverted through the critical state theory of soil mechanics.

[0037] Considering the influence of hydrate saturation on formation mechanical strength, the formation's mechanical parameters need to be corrected based on the hydrate saturation distribution.

[0038] In this embodiment, the full-size geomechanical model is an elastic model or an elastoplastic model.

[0039] S103. Quantitatively calculate the reservoir deformation caused by mining.

[0040] Among them, S103, quantitatively calculates the reservoir deformation caused by mining, including: based on the full-size geomechanical model and the bottom hole pressure during the mining stage, quantitatively calculates the stress field and displacement field of the reservoir and overlying layer caused by the reduction of bottom hole pressure.

[0041] Specifically, during the extraction of hydrates in marine areas, bottom hole pressure is a significant cause of formation subsidence. Based on a full-scale geomechanical model at the engineering scale, and combined with the bottom hole pressure during the extraction stage, the stress and displacement fields of the reservoir and overlying strata caused by the reduction in bottom hole pressure are quantitatively calculated.

[0042] Considering the radial seepage of fluid from the reservoir pores into the wellbore during depressurization extraction, it can be simplified to a steady-state seepage solution in a circular formation, which yields:

[0043]

[0044] In the formula, r w Let R be the radius of the well, and p be the range of influence of the seepage from the well. w To extract the bottom hole pressure, p e Let be the initial pore pressure of the reservoir, r be the distance between any position and the wellbore, and p(r) be the pore pressure at point r.

[0045] Considering the impact of increased effective stress on formation displacement, taking an elastic model as an example, the formation strain is:

[0046]

[0047] In the formula, ε is the strain of the formation, E is the elastic modulus, and v is Poisson's ratio.

[0048] S104. Calculate the displacement and stress of the entire well section of the production well.

[0049] Further, in this embodiment, S104, calculating the displacement and stress of the entire well section of the production well includes: using the displacement field and stress field of the reservoir and the overlying cover as boundary conditions, calculating the stress and displacement of the entire well section of the production well under the action of the stress and displacement field of the reservoir and the overlying cover, wherein the stress analysis includes one or more of the following: axial stress, bending stress, or shear stress of the casing, cement sheath, and screen pipe.

[0050] Specifically, considering the relative sliding between the cement sheath and the formation interface, the plastic displacement increment generated by the interfacial shear stress can be calculated based on the cohesion and friction coefficient of the formation interface.

[0051] To improve calculation speed and accuracy, the model size for stress analysis of casing and cement ring is usually limited to within 10 meters.

[0052] In particular, considering the possible slip surfaces or shear zones within the reservoir and overlying layer, the shear stress analysis requires assuming that the local displacement field is transformed into shear displacement.

[0053] S105. Based on the displacement and stress analysis of the entire well section of the production well, infer the risk areas of wellbore integrity.

[0054] Among them, the risk areas for wellbore integrity include areas where the wellbore structure is at risk of wellbore integrity under the stress and strain of the reservoir and overlying strata, as well as potential risk areas under the action of fault slip boundaries.

[0055] Based on the mechanical analysis results of the casing and cement sheath, the areas where wellbore integrity risks may occur under the displacement of the reservoir and overlying cover layer are identified.

[0056] S106. Design solutions to mitigate risks.

[0057] Among them, S106, designing risk mitigation solutions, including: adjusting the build-up point, build-up section length, well type structure, and well spacing parameters of hydrate production wells so that the wellbore structure avoids areas where wellbore integrity risks occur.

[0058] The method for predicting the integrity of marine hydrate production wells provided in this application includes the following steps: analyzing logging data and core samples; establishing a full-scale geomechanical model based on the logging data and core samples; quantitatively calculating the reservoir deformation caused by production; calculating the displacement and stress of the entire production well section; inferring the risk area of ​​wellbore integrity based on the displacement and stress analysis of the entire production well section; designing solutions to mitigate the risk; by calculating the displacement and stress of the entire production well section, the method effectively predicts the integrity risk of production wells caused by formation subsidence, enabling the prediction of wellbore integrity risk areas during the formulation of marine hydrate development plans and allowing for corresponding adjustments in wellbore trajectory design, thereby reducing the wellbore integrity risk of marine hydrate production wells and increasing the safety and reliability of production wells.

[0059] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0060] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for predicting the integrity of marine hydrate extraction wells, characterized in that: Includes the following steps: Analyze well logging data and coring samples; Based on the well logging data and the core samples, a full-size geomechanical model was established. Quantitatively calculate the reservoir deformation caused by mining; Calculate the displacement and stress of the entire well section; Based on the displacement and stress analysis of the entire well section, the risk areas for wellbore integrity are inferred; Design solutions to mitigate risks.

2. The method for predicting the integrity of marine hydrate extraction wells according to claim 1, characterized in that: The well logging data includes lithology, clay content, three-phase saturation of gas-water-hydrate, porosity, and permeability.

3. The method for predicting the integrity of marine hydrate extraction wells according to claim 1, characterized in that: The core sample includes the distribution of elastic modulus, Poisson's ratio, cohesion, and friction angle parameters along the depth.

4. The method for predicting the integrity of marine hydrate extraction wells according to claim 1, characterized in that: The full-size geomechanical model is an elastic model or an elastoplastic model.

5. The method for predicting the integrity of marine hydrate extraction wells according to claim 1, characterized in that: The quantitative calculation of reservoir deformation caused by mining includes: Based on the full-size geomechanical model and the bottom hole pressure during the mining stage, the stress and displacement fields of the reservoir and overlying strata caused by the reduction in bottom hole pressure are quantitatively calculated.

6. The method for predicting the integrity of marine hydrate extraction wells according to claim 5, characterized in that: During depressurization extraction, the fluid in the reservoir pores undergoes radial seepage into the wellbore. The steady-state seepage in a circular formation is solved as follows: In the formula, r w Let R be the radius of the well, and p be the range of influence of the seepage from the well. w To extract the bottom hole pressure, p e Let be the initial pore pressure of the reservoir, r be the distance between any position and the wellbore, and p(r) be the pore pressure at point r.

7. The method for predicting the integrity of marine hydrate extraction wells according to claim 6, characterized in that: The strain of the strata is: In the formula, ε is the strain of the formation, E is the elastic modulus, and v is Poisson's ratio.

8. The method for predicting the integrity of marine hydrate extraction wells according to claim 1, characterized in that: The calculation of displacement and stress throughout the entire well section includes: Using the displacement and stress fields of the reservoir and overlying cover as boundary conditions, calculate the stress and displacement of the entire well section under the action of the stress and displacement fields of the reservoir and overlying cover. The stress analysis includes one or more of the following: axial stress, bending stress, or shear stress of the casing, cement sheath, and screen.

9. The method for predicting the integrity of marine hydrate extraction wells according to claim 1, characterized in that: The risk areas for wellbore integrity include areas where the wellbore structure is at risk of wellbore integrity under the stress and strain of the reservoir and overlying strata, as well as potential risk areas under the action of fault slip boundaries.

10. The method for predicting the integrity of marine hydrate extraction wells according to claim 1, characterized in that: The design-based risk mitigation solutions include: Adjust the build-up point, build-up section length, well structure, and well spacing parameters of hydrate production wells to ensure that the wellbore structure avoids areas where wellbore integrity risks may occur.

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