A Poroelastic Analysis to Address the Impact of Depletion Rate on Wellbore Stability in Openhole Horizontal Completions

摘要

This paper highlights the development of a coupledrnporoelastic geomechanical and fluid flow model whichrnincorporates field and lab data with the objective to constrainrnthe full in-situ stress tensor and rock strength in order tornpredict the stability of open hole horizontal completionsrnduring reservoir depletion.rnResults of a four-year comprehensive testing and monitoringrnprogram conducted to assess the extent of hole instabilityrnduring shut-in and flowing periods1 indicated that there was nornimmediate hole collapse. However, the study revealed thernneed to assess the long-term impact of reservoir depletion andrnpressure drawdown on wellbore stability.rnThe results of this study indicate that the in situ stress state canrnbe characterized by a normal faulting environment with lowrndifferential stresses in which the maximum principal stress isrnapproximately equal to the overburden. Furthermore, arndetailed analysis of wellbore stability during productionrnsupports openhole completion for horizontal wells under therncondition that reservoir depletion is limited to a maximumrnpressure drop of 1,500 psi. This finding is independent of wellrnazimuth. Pressure drops exceeding 1,500 psi in the reservoirrnare likely to cause considerable wellbore instabilities. Thesernresults were achieved under the assumption of moderate tornmore pronounced amounts of drawdown (500-1000 psi) in thernnear wellbore region. The study also highlighted thatrnlaboratory-derived rock strength values from triaxial tests, arernlow and are not consistent with the drilling and productionrnexperiences to date in the field. Rather, the formation appearsrnto behave in a plastic manner that strengthens the wellbore.