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Fluid-Driven Fracture Initiation During Loss of Control Situations
  • Andreas Michael,
  • Ipsita Gupta
Andreas Michael
Louisiana State University

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Ipsita Gupta
Louisiana State University
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Abstract

If a kick is not detected and circulated properly out of the wellbore with heavier mud weight, it leads to blowouts. In this case, reservoir fluids gush out of the well uncontrollably without restriction leading to loss of control. This may lead to fractures initiating in the post-blowout capping stages, just below the casing shoe, propagating upwards creating a channel through which reservoir fluids can flow to the ocean floor. Being able to model these fracture failures will help understand wellbore integrity problems from loss of control situations and predict the possibility of broaching preventing many ecological disasters like the 1969 Santa Barbara oil spill from Union Oil’s A-21 well. The hypothesis tested is that fracture initiation from a wellbore in a loss of control situation can be predicted through analysis of the near-wellbore stress field, with knowledge of the in-situ stress state and the properties of the formation and the borehole assembly. A 3D numerical model is employed to assess whether a fracture will initiate. This is done by considering the stressfield at the casing shoe; the point most vulnerable to tensile fracture failure downhole. In-situ stress state, wellbore pressure, casing shoe depth and the casing, cement, and formation’s mechanical properties are independent variables that are shown to control fracture initiation; the dependent variable. A reservoir model is used to predict pressure build-up during capping procedures. A case study on Gulf of Mexico is presented with input wellbore pressure data generated using a worst case discharge model. Wellbore pressure drop during uncontrolled discharge from a well can cause casing collapse failures and subsequently pressure build-up in the post-blowout capping stage, may initiate fractures which can lead fluid leakage to the surface either through the cement or the interfaces with the casing and the formation. The region of the in-situ stress states where fracture initiation will occur is shown in dimensionless plots. This is useful for drilling and wellbore integrity teams. When targeting highly-pressured formations as in deepwater, wellbore architecture must be made with considerations of the wellbore pressures generated from loss of control situations like blowouts. Research reported in this publication was supported by an Early-Career Research Fellowship from the Gulf Research Program of the National Academies of Sciences, Engineering, and Medicine. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Gulf Research Program of the National Academies of Sciences, Engineering, and Medicine.