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EP-4735733-A1 - A METHOD OF AND A DEVICE FOR EVALUATING COLLAPSE BEHAVIOUR OF A BOREHOLE WALL

EP4735733A1EP 4735733 A1EP4735733 A1EP 4735733A1EP-4735733-A1

Abstract

A method of evaluating collapse behaviour of an open hole wall based on a constitutive soil model characterising surrounding soil of the open hole is disclosed. The method is performed by a processor and comprises the steps of: obtaining geometrical parameters of an axisymmetric slice of the open hole and the surrounding soil; creating a numerical model comprising a mesh having a plurality of elements representing the axisymmetric slice of the open hole and the surrounding soil, based on the obtained geometrical parameters; assigning simulation parameters to the numerical model, the simulation parameters comprising initial stresses, constitutive soil model properties and initial boundary conditions; determining that one or more boundary elements of the mesh develop a deformation larger than a deformation threshold, by updating the mesh during a time stepping process; removing the one or more boundary elements determined to develop a deformation larger than the deformation threshold; updating boundary conditions of the mesh; and repeating the determining, removing and updating steps until a defined criterion is met. Unlocking insights from Geo-Data, the present invention further relates to improvements in sustainability and environmental developments: together we create a safe and liveable world.

Inventors

  • ERBRICH, CARL THEODORE
  • AMODIO, Alessandro

Assignees

  • FNV IP B.V.

Dates

Publication Date
20260506
Application Date
20240617

Claims (15)

  1. 1. A method of evaluating collapse behaviour of an open hole wall based on a constitutive soil model characterising surrounding soil of the open hole, the method performed by a processor and comprising the steps of: obtaining geometrical parameters of an axisymmetric slice of the open hole and the surrounding soil; creating a numerical model comprising a mesh having a plurality of elements representing the axisymmetric slice of the open hole and the surrounding soil, based on the obtained geometrical parameters; assigning simulation parameters to the numerical model, the simulation parameters comprising initial stresses, constitutive soil model properties and initial boundary conditions; determining that one or more boundary elements of the mesh develop a deformation larger than a deformation threshold, by updating the mesh during a time stepping process; removing the one or more boundary elements determined to develop a deformation larger than the deformation threshold; updating boundary conditions of the mesh; and repeating the determining, removing and updating steps until a defined criterion is met.
  2. 2. The method according to claim 1, wherein the constitutive soil model captures friction and dilation response of the surrounding soil.
  3. 3. The method according to claim 2, wherein the constitutive soil model comprises an elastic- plastic, Mohr-Coulomb, pure frictional cohesion-free soil model.
  4. 4. The method according to any of the previous claims, wherein the mesh is a two- dimensional mesh.
  5. 5. The method according to any of claims 1 to 3, wherein the mesh is a three-dimensional mesh.
  6. 6. The method according to any of the previous claims, wherein the determining step comprises determining that a vertical displacement of a boundary element exceeds a displacement threshold.
  7. 7. The method according to claim 6, wherein the displacement threshold is a half of a vertical height of the boundary element.
  8. 8. The method according to any of the previous claims, wherein the updating step comprises applying boundary conditions applied to the deleted boundary elements to a new boundary element(s).
  9. 9. The method according to any of the previous claims, further comprising, prior to the step of determining that one or more boundary elements of the mesh develop a deformation larger than a deformation threshold, the steps of: determining that a velocity of a boundary element is higher than a velocity threshold; performing mechanical time stepping at constant time until element displacements of the boundary element have stabilised or the element displacements have increased to a point where the boundary element has to be deleted.
  10. 10. The method according to any of the previous claims, wherein the defined criterion comprises when a required design stable duration of the open hole is reached while a percentage of collapsed element is lower than a threshold value.
  11. 11. The method according to any of the previous claims, wherein the defined criterion comprises when collapse of the open hole exceeds a collapse threshold before a required design stable duration of the open hole is reached.
  12. 12. The method according to any of the previous claims, wherein the open hole comprises an underwater open hole.
  13. 13. The method according to any of the claim 12, wherein the boundary conditions comprise cyclic tidal variations, specifically with or without application of a static positive head over and above an instantaneous water pressure imposed from the sea.
  14. 14. A device for evaluating collapse behaviour of an open hole wall based on a constitutive soil model characterising surrounding soil of the open hole and by utilizing a mesh having a plurality of elements representing an axisymmetric slice of the open hole and the surrounding soil, the mesh created based on parameters of the axisymmetric slice of the open hole and the surrounding soil, the device comprises a processor for performing the method according to any of the previous claims 1 to 13.
  15. 15. A computer program product, comprising a computer readable storage medium storing instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any of the claims 1 to 13.

Description

A METHOD OF AND A DEVICE FOR EVALUATING COLLAPSE BEHAVIOUR OF A BOREHOLE WALL FIELD OF THE INVENTION [0001] The present disclosure generally relates to the field of open hole stability, and more specifically to a method of and a device for evaluating collapse behaviour of a borehole wall. Unlocking insights from Geo-Data, the present invention further relates to improvements in sustainability and environmental developments: together we create a safe and liveable world. BACKGROUND OF THE INVENTION [0002] Drilled and grouted piles from the foundation for many offshore infrastructures. These infrastructures serve various traditional industries like oil and gas, bridge construction and for new applications such as wind energy industry. The successful installation of drilled and grouted piles requires a stable open hole to be drilled first. [0003] The analysis of an open hole is crucial for assessing borehole stability. The analysis of open hole stability refers to the assessment and evaluation of the stability of the drilled hole before the grouting process and the subsequent installation of piles. This process is crucial for ensuring the integrity and stability of the piles and their ability to withstand the loads imposed on them. [0004] The stability analysis considers factors such as soil or rock strength, formation stability, pore pressure, and water inflow during the drilling and grouting processes. This analysis helps to determine the stability of the open hole and ensures that the grouted pile will be adequately supported by the surrounding soil or rock formations. In this context, 'grouting' denotes the injection of a cement-based fluid into a drilled hole to enhance pile stability and bonding with the surrounding geology in pile construction, especially offshore. [0005] It is noted that a marine environment often involves uncemented soils such as sand with high permeability. In uncemented soils, the length of time over which a drilled open hole may remain stable depends on the soil strength, stiffness and drainage behaviour. [0006] Moreover, specifics of offshore open hole pile construction - namely drilling with water, not mud, and sometimes application of a positive head drilling set-up are not seen as often in onshore construction. [0007] The inventors are aware of an analysis of open hole stability based on finite element analyses. This analysis included time dependent analysis but with a mesh that could not exhibit failure in critical layers and with a non-calibrated soil model that could not capture appropriate soil behaviour. [0008] No attempt was made to follow the steady propagation of any collapse beyond the point of first initiation. However, the importance of a model that can capture the propagation of collapse beyond first initiation is a conceptual leap and of much importance in drilled and grouted piles construction, especially for the offshore environment. [0009] Based on the above, there is a general and ongoing need for a method of evaluating collapse behaviour of a borehole wall, especially evaluating the ongoing propagation of hole collapse over time with the eroding wall feature in uncemented soil. BRIEF SUMMARY OF THE INVENTION [0010] According to one aspect of the present disclosure, there is presented a method of evaluating collapse behaviour of an open hole wall based on a constitutive soil model characterising surrounding soil of the open hole, the method performed by a processor and comprising the steps of: [0011] - obtaining geometrical parameters of an axisymmetric slice of the open hole and the surrounding soil; [0012] - creating a numerical model comprising a mesh having a plurality of elements representing the axisymmetric slice of the open hole and the surrounding soil, based on the obtained geometrical parameters; [0013] assigning simulation parameters to the numerical model, the simulation parameters comprising initial stresses, constitutive soil model properties and initial boundary conditions; [0014] - determining that one or more boundary elements of the mesh develop a deformation larger than a deformation threshold, by updating the mesh during a time stepping process; [0015] removing the one or more boundary elements determined to develop a deformation larger than the deformation threshold; [0016] - updating boundary conditions of the mesh; and [0017] - repeating the determining, removing and updating steps until a defined criterion is met. [0018] The method is based on the insight that the collapse behaviour of an open hole over time can be properly modelled by an interactive procedure in which one or more boundary elements considered as representing a fallen part of the surrounding soil are removed. The removal of such boundary elements allows updated boundary conditions to be applied to new boundary elements of the constitutive soil model representing the axisymmetric slice of the open hole and the surrounding soil. Propagation of the hole collapse over tim