Geomechanics Successfully Implemented in a Deepwater Setting

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202146, “Successful Implementation of Geomechanics in a Deepwater Setting: A Case Study From KG Offshore India,” by Sarah Bhimpalli, ONGC; Ashok Shinde, Baker Hughes; and Bayye L. Rao, ONGC; et al. The paper has not been peer reviewed. _ Geomechanics plays an important role in assessing formation integrity during well construction and completion. In the complete paper, study field K belongs to a Plio-Pleistocene sequence in a deepwater environment with hydrocarbon prospects. As a part of exploration activity, four existing offset oil wells were considered for geomechanical model construction. The geomechanical model for the field was built by integrating available drilling, geology, petrophysics, and reservoir data. The methodology adopted in this paper highlights how a reliable geomechanical model can be built for a field with data constraints. Introduction The present study block is in deep water off the eastern Indian coast in the KG basin, with several hydrocarbon discoveries in a clay formation. These reservoirs have been deposited under marine conditions, and source rock is thought to be Eocene to Oligocene marine shale. During drilling, as the rock on the wellbore track was drilled and brought out of the hole, the drilling fluid would exert a corresponding pressure on the wellbore wall and the stress of the rock surrounding the wellbore would be redistributed, generating induced stress. To maintain wellbore stability, use of a drilling fluid of appropriate density (mud weight) to control induced wellbore stress is essential. Shear and tensile failures are the major causes of mechanical instability in boreholes. If it rises past the appropriate upper limit, drilling-fluid pressure can cause tensile failure in the wellbore wall; if lower than the appropriate lower limit, drilling-fluid pressure can cause shear failure in the wellbore wall. Because of several drilling complications and nonproductive time experienced during the exploratory phase, building of a geomechanical model for safe and cost-effective drilling during the development phase is necessary. The existing four wells (W, X, Y, and Z) targeted the hydrocarbon play. Using the data from the four offset wells, a comprehensive geomechanical study was completed. The main objectives of the study included pore-pressure prediction, wellbore-stability analysis, well-trajectory optimization, and sanding prediction. 1D Geomechanical Modeling To analyze wellbore stability, well logs, laboratory test results, and drilling reports of the wellbore were used to determine geomechanical characteristics of the drilled formations. The elastic properties, rock strength characteristics, in-situ stresses, and pore pressures are the most important geomechanical characteristics to be measured or calculated. The geomechanical model was built by integrating drilling, geology, petrophysics, and reservoir engineering data. The work flow to build the geomechanical model is presented in Fig. 2 of the complete paper. Vertical stress (Sv) was estimated by integration of density logs from seabed to reservoir. Pore pressure was predicted using normal compaction trend (NCT) on log data. Minimum horizontal stress (Shmin) was constrained using leakoff tests (LOTs) and mini- and microfracturing data. No rock-mechanical testing data were available, and rock properties were estimated from petrophysical logs using regional experience. Magnitude and orientation of maximum horizontal stress (Shmax) was constrained using the presence of stress-induced wellbore failures on image and caliper logs.