Wellbore stability in naturally fractured formations featuring dual-porosity/single-permeability and finite radial fluid discharge

Formation damage prevention using microemulsion in tight sandstone gas reservoir

Dynamic stress distribution around the wellbore influenced by surge/swab pressure

Relationship between the gas hydrate suppression temperature and water activity in the presence of thermodynamic hydrate inhibitor

Mechanical characteristics of well cement under cyclic loading and its influence on the integrity of shale gas wellbores

The loadings which act on the wellbore are more frequently dynamic than static, such as the surge/swab pressure caused by tripping operations. The changing rate of loading could induce a change in wellbore stress and result in wellbore instability. The conventional Kirsch solution to calculate wellbore stress is only applicable to the steady state without considering the coupled deformation–diffusion effect. To account for these deficiencies, this paper introduces a coupled poroelastodynamics model to obtain wellbore stress distribution under dynamic loading. The model is solved by the implicit finite-difference method with the surge/swab pressure caused by tripping operations taken as the specific dynamic loading source. Then, failure criteria are applied to analyze dynamic wellbore stability and the hemisphere plots of minimum mud density (MMD) to avoid wellbore collapse are generated. The effect of in-situ stress regimes, failure criteria, and permeable properties on the instability of the borehole has been investigated, and the applicability and accuracy of the conventional failure criteria for dynamic loading conditions have been studied by the extensive triaxial compression tests performed on Bedford limestone under different strain rates. Furthermore, two specific cases have been analyzed and results show that compared with the poroelastodynamics model, the conventional method either overestimates or underestimates the MMD, the difference of which can be as significant as 0.11 g/cm3. Not limited to the tripping operations, the developed poroelastodynamics model can be applied to any specific dynamic loading conditions with the fluid inertia neglected.

Dynamic Wellbore Stability Analysis Under Tripping Operations

Real-Time Wellbore Stability Evaluation for Deepwater Drilling During Tripping

\n This paper identifies wellbore-stability concerns caused by transient swab/surge pressures during deepwater-drilling tripping and reaming operations. Wellbore-stability analysis that couples transient swab/surge wellbore-pressure oscillations and in-situ-stress field oscillations in the near-wellbore (NWB) zone in deepwater drilling is presented.\n A transient swab/surge model is developed by considering drillstring components, wellbore structure, formation elasticity, pipe elasticity, fluid compressibility, fluid rheology, and the flow between wellbore and formation. Real-time pressure oscillations during tripping/reaming are obtained. On the basis of geomechanical principles, in-situ stress around the wellbore is calculated by coupling transient wellbore pressure with swab/surge pressure, pore pressure, and original formation-stress status to perform wellbore-stability analysis.\n By applying the breakout failure and wellbore-fracture failure in the analysis, a work flow is proposed to obtain the safe-operating window for tripping and reaming processes. On the basis of this study, it is determined that the safe drilling-operation window for wellbore stability consists of more than just fluid density. The oscillation magnitude of transient wellbore pressure can be larger than the frictional pressure loss during the normal-circulation process. With the effect of swab/surge pressure, the safe-operating window can become narrower than expected. The induced pore pressure decreases monotonically as the radial distance increases, and it is limited only to the NWB region and dissipates within one to two hole diameters away from the wellbore.\n This study provides insight into the integration of wellbore-stability analysis and transient swab/surge-pressure analysis, which is discussed rarely in the literature. It indicates that tripping-induced transient-stress and pore-pressure changes can place important impacts on the effective-stress clouds for the NWB region, which affect the wellbore-stability status significantly.

Zahra Zamanipour

Papers

Dynamic stress distribution around the wellbore influenced by surge/swab pressure

Dynamic Wellbore Stability Analysis Under Tripping Operations

Real-Time Wellbore Stability Evaluation for Deepwater Drilling During Tripping

Transient Coupling of Swab/Surge Pressure and In-Situ Stress for Wellbore-Stability Evaluation During Tripping