Abstract

EOR is key to the longer term business performance of Petroleum Development Oman (PDO). The "A" Steam Project in Southern Oman is a large scale EOR project currently being executed by PDO. It comprises the re-development of the "A" West Field, which has a significant prior cold oil development history, and the new development of the nearby "A" East Field.

The heavy viscous oil in both fields is contained in high net-to-gross braided river, aeolian and alluvial fan sandstones of the Cambrian Haima Group. Both fields were discovered in the 1970's. The "A" West Field has lower oil viscosity and was first produced in 1976. "A" East oil is significantly more viscous than "A" West oil and was believed to be too viscous to be produced by cold production, so "A" East Field was not developed. By 2008, after some 30 years of cold oil production, an estimated 18% of the STOIIP had been recovered from "A" West and the water cut steadily increased to 95%.

A field study was initiated in 2008 to evaluate re-development options based on EOR technologies. The selected Phase I (re-)development concept comprised a steam flood with fifty 10-acre / 7-spot patterns in "A" West and initial cyclic steam soak (CSS) with 74 wells on a regularly spaced 92 × 92 m grid in "A" East, with conversion later to a 8 acre / 9 spot steam flood. The two sub-surface developments were to be managed as an integrated project with shared surface facilities and operations. The project received FID for Phase I in 2009 and this is currently being executed. After the successful testing of cold production in selected new "A" East wells, a change to the Phase I FDP was implemented with the decision to cold produce the 32 most crestal wells prior to CSS in "A" East.

To de-risk the project, the more complex "A" West Field is being re-developed in a phased manner. Following field trials, initial CSS is now used to improve the gross rate of poorly performing producers, which constitutes a change to the FDP. To investigate the economic benefits of alternative patterns in areas of the field where steam flooding efficiency appears to be low, injection has recently started in two patterns which will become 10 acre / 10 spot trials. Additionally seven 3.3 acre / 7 spot trial patterns are being drilled on the western edge of the 10 acre / 7 spot development area.

Advanced time-lapse surveillance data acquisition techniques – DTS, DAS 3DVSP and HT optical pressure gauges - are deployed to support WRM optimization of the Phase I development, and to prepare the Phase II field (re-)development plan for the down-flank areas.

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