This paper presents a geomechanical study on the potential of wellbore instability and sand production for a multi-field gas development in offshore Peninsular Malaysia. The objectives of the study were 1) to develop strategies to maintain mechanical and time-dependent stabilities of extended reach wells, and 2) to assess sand production risk in the development wells and eliminate unnecessary downhole sand control. The data required for the study include: 1) in-situ stresses, including magnitude and orientation, and formation pressure, 2) mechanical and petrophysical properties of the formations transected by the wellbore, and 3) properties of drilling fluid and its interaction with shale formations. The likelihood of wellbore instability and sand production for the development wells was assessed using in-house developed wellbore stability and sand production prediction tools.
Mud weight stability profiles showing the variation of lower and upper bound mud weights with depth were developed for typical vertical wells. Critical mud weight contour plots which show the variation of lower and upper bound mud weights with wellbore azimuth and deviation angle for preventing mechanical wellbore instability were developed for various formations. In addition, a drilling fluid design methodology that can be used for quick and reliable determination of the optimum mud design (weight, type and chemistry) was developed for the fields.
Critical drawdown and critical reservoir pressure profiles for assessing sand production potential in the fields were established. Sand production was found not to be a major problem in the early stage of production. However, depletion in reservoir pressure and water-cut can significantly increase sand production risk.