History Match to Support Interpretation of Surfactant Flooding Pilot Test in Tanjung Field

Abstract

Tanjung Field is a brown field which pressure has already depleted and been supported by waterflooding for over a decade. To improve production, surfactant injection, is being studied to be employed in the field. The main objective of this study is to identify parameters that affect oil production increase. History match of the pilot test was carried out to improve the reliability of the reservoir model, hence improving the prediction result of surfactant injection forecast. History match of the pilot test has been carried out using CMG STARS commercial simulator by considering mechanism inferred from laboratory evaluation such as wettability alteration, surfactant retention, interfacial tension reduction and improvement of mobility control due to lower oil-surfactant emulsion viscosity. These parameters are initially perceived from laboratory result, upscaling and adjustment is applied to field model to further on do sensitivity study. Sensitivity analysis of every parameter is provided to better understand the effect of each mechanism that contributes to the oil incremental result. Stratigraphically, Tanjung Structure has 7 productive zones: Zone A, B, C, D, E, F and P. Reservoir Zone A has total estimated reserve of 193,732 MMSTB, with recovery factor of 16.3%. The zone consists of conglomerate sandstones with porosity of 21% and permeability ranging from 10 to 100 mD. The field produces light oil within 40 °API, 30% wax content and 1.14 cP of viscosity. T-119 is the well chosen to be injected due to its structural position that ease flow by gravity force to producer wells. Forecast simulation based on coreflood result has been conducted for pilot test. However, the result was very pessimistic in predicting incremental oil gain and breakthrough time after compared to pilot result. An attempt to history match the surfactant flood pilot is presented by considering phenomena that is not included in the forecast based on additional lab and field data.

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“…Several successful field applications have been recorded in various fields across the world such as Semonga field in Indonesia where injection of surfactants into the carbonate reservoir resulted in 8% reduction in water cut and increased oil recovery [33] and the Daqing oilfield (Chao 522 block) in China with a reported 30% increase in oil recovery from a single well after the injection of 1.0% nonionic surfactant [41]. Furthermore, Aslam et al [4] reported an increase in oil recovery during surfactant flooding using 2.05% anionic surfactant-A127 on Tanjung Field in Indonesia. Despite the success rate of surfactant flooding, the technique has suffered some major setback over the years due to certain factors such as the high cost of surfactant chemicals and its non-biodegradable nature [27].…”