Key Learnings From First 2 Years of a Full-Field CSS Development in Oman

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 179833, “Key Learnings From First 2 Years of a Full-Field CSS Development in Oman,” by Solenn Bettembourg, Steve Holyoak, Abdullah Alwazeer, Mohammed Manhali, Mohammed Rawahi, and Amur Habsi, Petroleum Development Oman, prepared for the 2016 SPE EOR Conference at Oil and Gas West Asia, Muscat, Oman, 21–23 March. The paper has not been peer reviewed. The A East Haradh formation contains a 200-m-thick oil column of highly viscous oil, with viscosity ranging from 200 to 400,000 cp. Because of the high viscosity, first production was considered possible only by the use of thermal enhanced-oil-recovery techniques, starting with cyclic steam stimulation (CSS). This paper presents key learnings derived during this initial-operations phase of CSS in the A East Field, including key trial results on different well completions and artificial-lift systems. Overview of Field Startup In light of the results of a new geochemical characterization study of the crude extracted from a core, cold production was deemed feasible in the crestal area of the field. Viscosities at the top of the Haradh were estimated at 200 cp, lower than previously thought, and progressing cavity pumps (PCPs) were installed in 32 wells to start a cold-production phase. Cold production started in March 2013 and lasted until the end of 2014, when all wells in the field were converted to CSS. The cold-production period allowed early depletion of the reservoir and later improvement in steam injection. A pressure drop of up to 20 bar was observed, and fluid-level measurement in the wells and PCP performance suggested good pressure communication between the wells. Despite some early challenges, first CSS production was promising and, within a few months, was ramped up to 70% of the targeted CSS field peak oil rates. Overview of CSS Performance A typical CSS cycle in an A East well is shown in Fig. 1, using the wellhead temperature sensor as an indicator. The cycle starts with the injection phase for several weeks (initially 4 to 6). After that, the well is closed for a soaking period of a few days and then opened for free flow, which lasts for up to 3 weeks. The well is intervened with a flush-by unit (FBU) to prepare for production, followed by starting the beam pump. At the end of the production cycle, the well is stopped on the basis of end-of-cycle criteria and intervened again to prepare the well for steam injection for the subsequent cycle. The overall cycle duration is typically between 100 and 300 days and is dependent on the performance of the well with respect to preset operating envelopes.