Observations From a Fieldwide Pressure Data Acquisition Campaign in the Wara Formation of the Greater Burgan Field, Kuwait

Abstract

Abstract The Wara reservoir has been producing for over 60 years and its pressure has slowly decreased over the years, now below saturation pressure in some structurally-high areas where gas cap has increased in size compared to very small initial gas caps in these areas. A peripheral, water injection project is being considered to maintain the pressure above bubble point and improve oil recovery from the flank areas. However, limited information is available concerning Wara reservoir heterogeneity. Shut-in of all Wara producers provided an "once-in-a-lifetime" opportunity to carry out a fieldwide pressure data acquisition campaign. Over a period of six months (Nov. 2006-May 2007), 127 static bottom-hole pressure (SBHP) surveys, 26 pressure buildup (PBU) tests (including buildup tests for 2 active wells of the interference test program) and 3 interference tests were conducted. Each interference test involved one active well and 3-6 observation wells. This paper describes a systematic methodology to select wells to test on a fieldwide basis, test design exercise, data acquisition program execution, and observations and conclusions reached from this data set. Over the duration of the campaign, an increasing pressure trend was observed in almost all wells slated for PBU and interference tests. This observation was made possible due to multiple SBHP recordings in these wells. The linearly-increasing pressure trend had to be taken into account in the analyses of the buildup tests to avoid interpreting wrong boundary conditions. Wellbore dynamics also initially affected some pressure buildup tests and were later circumvented by the use of a downhole shut-in tool (DHST) to limit the phase segregation effect. The transient analyses revealed different flow regimes, from infinite-acting radial flow, to dual-layer and radial composite with or without sealing faults. From the SBHP data, maps have been made to assist in identifying compartments. One interference test showed anisotropy which could be critical in the implementation of a water injection project. Overall, the interpretation of the data from this extensive data acquisition campaign has shed light on reservoir heterogeneities that have been integrated with changes made in a full-field, "Wara only", history-matched simulation model.