--> Geomechanics Considerations for Safe Drilling of ERD Wells in Western Offshore, India

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Geomechanics Considerations for Safe Drilling of ERD Wells in Western Offshore, India

Abstract

For safe and economic drilling operations, especially in high angle wells located offshore, geomechanical assessment and solutions have even more important role to play in decision-making for drilling these wells efficiently as the safe mud weight window tend to be narrow. Major drilling problems include kick, stuck pipe, tight spot, hole packoff, unscheduled sidetrack, loss of tools etc. which unnecessarily increase non-productive time, inflate the costs of drilling and impact the quality of critical formation evaluation data. This paper describes geomechanical studies performed for three extended reach development (ERD) wells which were drilled safely in offshore, Bassein field, India. It was identified that drilling through shales overlying target reservoir (Bassein and Mukta limestone) caused the maximum NPT in the vertical exploration wells with over gauged hole conditions leading to poor data quality. A pre-drill geomechanical model was built for each ERD well using available data in the exploration wells to assess the drilling risks and to facilitate minimizing the impact of geomechanical problems. The main challenge was drilling safely through the shale formations (Alibagh, Mahim and Tapti) with well deviation in range of 50–70 deg and maintaining adequate hole cleaning. Sensitivity analysis was conducted for different well deviations and azimuths with quantitative risk assessment (QRA) of rock elastic and mechanical properties in the final mud weight recommendation and casing policy. Fracture gradient has been found to be varying in different shale formations using poroelastic horizontal strain method and validated using direct measurements like LOT, XLOT and MDT stress testing. Equivalent circulation density (ECD) and drilling parameters were monitored in real-time for proper hole cleaning. With the depletion of reservoir pressure, mud weight plan was revised for drilling the horizontal well which avoided losses and differential sticking.