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

Abstract

Summary 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. 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. 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. 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.

Numerical Investigation of the Effect of Swab and Surge Pressure on the Time-Dependent Wellbore’s Development of Natural Fractures

“…Finally, after integrating swab and surge pressure, a drilling mud that was initially in the safe region can slip out into the unstable region, therefore the time dependent safe mud weight should be employed to provide accurate results for the wellbore stability analysis. These findings are in line with the findings of (Zhang et al 2018) who showed that incorporating swab/surge pressure into the wellbore stability study resulted in a smaller mud weight window than expected.…”

“…The low permeability of the rock formation utilized in this study (5md) also prevents the variation of the pore pressure with the swab and surge pressure in the near wellbore region. The influence of transient swab and surge pressure on the real-time wellbore stability was also examined by (Zhang et al 2018) and they got opposite results with the current study: Their results showed that transient swab and surge pressure affect pore fluid pressure in the surrounding wellbore area, and the effect on the pore pressure declines when going farther away from the wellbore. The discrepancy between the two results is due to the fact that the rock permeability utilized in this simulation (5md) is lower than the permeability employed in the (Zhang et al 2018) study (10 md).…”

“…The Biot's theory of poroelasticity governs the deformation of porous media, whereas the continuum equation and Darcy's theory define pore fluid flow. The governing equations of these two processes have been extensively analyzed in several publications (Fjaer et al 2008;Jaeger et al 2009;Zielonka et al 2014;Feng and Gray 2018a). Therefore, these equations will not be repeated in the current study.…”

“…The investigations which aimed to evaluate the effect of swab and surge pressures on the wellbore stability are scarce in the literature: Zamanipour et al (2016) demonstrated that the induced stress initiated by the transient surge pressure continuously increased and then decreased with the time; then, the radial stress evolved in the same trend with the induced stress caused by the transient surge pressure; finally, the total tangential stress displayed an opposite behavior with the induced stress, it first declined and then rose with the time. Zhang et al (2018) equally found that swab and surge pressure had a substantial impact on the near wellbore stress and pore pressure. Moreover, Meng et al (2019) have developed a poro-elasto-dynamic model to quantify the minimal mud density required to ensure the stability of the wellbore while subjected to changes induced by swab/surge pressures.…”

Transient Stress Distribution and Failure Response of a Wellbore Drilled by a Periodic Load

“…Zamanipour et al [8] investigated the wellbore stress distribution and wellbore stability when transient surge stress is generated in a directional wellbore during tripping process. Zhang et al [9] conducted wellbore stability analysis by coupling transient swab/surge model and poromechanical solution during tripping and reaming processes and proposed a work flow to obtain safe mud-weight window. Meng et al [10] developed a coupled poroelastodynamic model to obtain dynamic stress distribution around the wellbore.…”