Abstract
Abstract
Mukhaizna is a heavy oil field in southern Oman operated by Oxy. It is a multi-stacked reservoir under steamflood since 2007. The main sandstone reservoirs were developed using horizontal producers in each target zone supported by vertical injectors.
Although most of the patterns are thermally mature, a few areas are still awaiting steamflood response. Hence, different options were evaluated across the field to help establishing thermal processing in areas with such a delay in steam response. One of the options considered and trialed was a Steam-Assisted Gravity Drainage (SAGD) in a pattern with two horizontal producers (HPs) originally drilled within the same zone. The subject pattern is characterized with thin, discontinuous shale baffles that have limited the communication between the upper producer and the supporting injectors. Therefore, a modified SAGD configuration that involved converting the upper producer as an injector was considered to help sweeping the remaining oil in the upper sand. Additionally, analog SAGD projects were also evaluated to increase the chance of success although the target reservoir is not ideal for typical SAGD.
As this pattern was originally supported by a continuous steamflood, the same was continued to avoid any change in operating conditions around the SAGD trial. As a result, liquid production rate gradually increased from the lower producer after converting the upper producer into steam injection associated with increase in water cut initially. However, oil rate started to improve with a continuous increase in pumping speed. Salinity test of produced water showed significant increase over the expected level of condensed steam which could be attributed to either water encroachment from edge aquifer or high TDS in the injected low steam quality hot water. Nevertheless, the lag in oil response suggests most of the incremental oil resulted from the initiation of the SAGD trial that has changed the pressure dynamics in the reservoir and provided additional mean to deliver some heat and displacement forces to unswept areas although steam chamber was most likely not developed due to the low steam quality of injected steam.
This paper describes the potential, challenges, and opportunities of using a modified SAGD configuration in Mukhaizna heavy oil field in sub-optimum operating conditions for SAGD projects in terms of depth, thickness, patterns, and well configuration.