A deepwater operator in Asia Pacific required a large volume fluid sample from a gas reservoir in the northwest shelf of Australia for accurate non-hydrocarbon gas content analysis. This paper highlights pre-job planning and operational considerations for running logging while drilling (LWD) fluid sampling and formation pressure testing devices in two highly deviated 8 ½-in wellbores. These include risk mitigation techniques to avoid stuck pipe, accommodating rig heave associated with deepwater drill ships, oil-based mud (OBM) gas sampling issues and the prevention of geo-chemical absorption.
Because the wells reached more than 80°inclination, traditional, wireline fluid sampling required a pipe-conveyed or tractor mechanism, increasing the AFE, rig time and operational risks. To make sampling feasible required the use of a unique LWD solution. Furthermore, the planning, mobilization, and deployments were accomplished in less than six weeks by seamless cooperation between the operator and service partner.
In two runs, 26 samples were acquired containing more than 19 liters of fluid. During the pre-sample cleanup, a high- speed telemetry system provided 25 bits per second of real-time fluid analysis data to ensure the fluid properties were stabilized. Because of the improved operational efficiency of logging while drilling technology, the operator estimated savings of approximately USD10 million dollars in rig and operating costs and potentially millions more in reduced retrofitting costs of the production facility.
Fluid sampling while drilling technology represents a major change in deepwater formation evaluation capabilities. By utilizing the techniques presented in this paper, operators can collect large volumes of fluid samples in deviated wells while reducing operational risks and minimizing costs. A recap of the two wells presents best practices for prejob planning, risk mitigation and overcoming mobilization challenges in short call-out scenarios. These high-quality development well samples enable a properly designed production facility, thereby preventing costly post-production modifications.