Single-Gradient Subsea-Mud-Lift-Drilling Technology in Deepwater Gulf of Mexico

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 174881, “Successful Testing of Single-Gradient Subsea-Mud-Lift-Drilling Technology in Deepwater Gulf of Mexico,” by Sharifur Rahman, Calvin Holt, David Dowell, Danilo Morales, and Siri Davis, Chevron, prepared for the 2015 SPE Annual Technical Conference and Exhibition, Houston, 28–30 September. The paper has not been peer reviewed. Subsea-mud-lift-drilling (SMD) technology is a form of managed-pressure drilling (MPD). As with other MPD systems, SMD technology offers early detection of influxes (kicks) and minimizes downhole losses to weak subsurface formations. However, significant differences are built into the SMD system. This paper will highlight the benefits of single-gradient SMD (SMD-S) technology, the execution of the most recent deployment, and test results that represent the final steps in moving toward continued MPD operations in the deepwater Gulf of Mexico (GOM). Introduction SMD is a sophisticated subsea MPD technology development and commercialization project that has just completed its fourth offshore deployment. With every deployment, the learnings have been captured and addressed successfully. The most recent deployment in the deep water GOM has demonstrated that the technology works as designed by successfully accomplishing nearly all test objectives. The confidence is now very high that the industry will see the successful commercial delivery of a drilling technology that offers potential for a more-efficient drilling operation. In addition, this technology will lead ultimately to enhanced production and recovery from deepwater assets. SMD has two operational modes, SMD-S and dual-gradient SMD (SMD-D), as illustrated in Fig. 1. SMD-D. A fluid with a density equivalent to seawater is used in the riser and a heavier mud weight is used below the mudline. This combination of gradients results in an annular-pressure profile that more closely follows the natural pore-pressure and fracture-gradient trends. This significantly improves the ability to stay within the pressure window much longer without changing mud weights. Dual-gradient drilling helps to eliminate casing points that are required in conventional drilling and offers significant production benefits in the deepwater environment. In order to maintain constant bottomhole pressure (BHP), this technique allows annulus pressure to be trapped below a subsea rotating control device (SRD) during connections by increasing the maximum-lift-pump (MLP) inlet pressure to help manage ballooning or control wellbore stability.