Formation Tester and NMR Heavy Oil Characterization during Placement of a Horizontal Injector at a Tar/Oil Interface

摘要

A case history is presented for a horizontal injector well drilled at the base of a moveable oil column on top of a tar mat in a carbonate oil reservoir in the Middle East. The well was placed utilizing real-time logging-while-drilling (LWD) nuclear magnetic resonance (NMR) oil viscosity correlations and formation tester mobility data. As this was a pilot water injector placed at an oil/tar interface with limited historic oil viscosity vs. depth data, obtaining quality calibration oil samples was considered critical. Both LWD and pipe conveyed tough logging conditions (TLC) formation tester data sets were acquired. Consequently, direct comparisons of LWD acquired and TLC acquired formation pressures and formation mobilities were possible. The comparison proved the reliability of the LWD formation mobility data. The LWD measured formation pressures, however, were supercharged compared to the TLC formation tester measured formation pressures, which were largely in line with expected formation pressures. The oil viscosity results from the TLC formation tester in situ viscosity fluid analyzer and from the NMR viscosity correlation compared favorably with the laboratory results from the fluid samples acquired by the TLC formation tester. This indicates that accurate real-time in situ fluid property determination is possible with a modern formation tester and NMR tools. In this reservoir, during the early phase of acquiring oil viscosity vs. depth data at the oil/tar transition zone, the main lesson learned was that the deeper section of the case study well contained higher asphaltene content, which caused the well-bore plugging that prevented reservoir access after suspending the well for tie-in. A clean out operation was unsuccessful, as plugging reoccurred. Current plans are for the well to be sidetracked again in the 3 centipoise (cP) to 20 cP oil interval at the top portion of the oil/tar transition zone.