Because of large potential reserves and increased global demand for oil and gas, deepwater exploration and development has become a key area for most E&P companies. Deepwater development challenges include higher hydrostatic and reservoir pressures, strong ocean currents, and ever-changing weather conditions. Therefore, a clear understanding of the requirements of this challenging environment is imperative to maximize safety and efficiently complete and commission wells for optimal reliability and reservoir recovery. Of particular concern are the completion activities on deepwater wells from dynamically positioned (DP) vessels. A key challenge is the reliable installation of subsea and completion equipment while maintaining well control. DP vessels require dependable subsea landing string technology capable of fast-acting operation that is independent of water depth. In an emergency, the system must perform a fully sequenced emergency shutdown and disconnect in as little as 15 seconds.
This study includes a review of the subsea landing string technology already in use in deepwater fields and the development of new technologies designed and qualified to meet the particular challenges associated with the Petrobras Cascade and Chinook fields in the Gulf of Mexico. These technologies included the use of a high-pressure-rated subsea test tree and an electrohydraulic operating system, coiled-tubing cutter module (CTCM), and project-specific equipment (e.g., slick joints, latch mandrels, and spacers). Special emphasis was placed on the validation testing performed on the hardware to assure functionality and reliable operations at project-specific conditions, including working at extreme hydrostatic pressures due to completion fluid weight and water depth. These tests included hydrostatic pressure testing at a simulated riser environment with respect to pressure and temperature (7,500-psi hydrostatic pressure, 15,000-psi bore pressure, 275 degF), validation of ball valve cutting capabilities for specified coiled tubing, and qualification of new hardware.
Engineering efforts, planning, and preparation resulted in the completion of Cascade#4 and Chinook#4 without safety or environmental incidents and within the planned cost and schedule.
Technical Paper presented at 15th Rio Oil & Gas Conference, held in Sep 13 - 16th, 2010 at Rio Centro/RJ.