Abstract

Tunu is multilayer gas field operated by Total EP Indonesie in Kutai Basin, which produced since 1990. It consists of thousands of gas-bearing sandstone reservoirs; spread over 2000 meters of vertical gross thickness. The depositional environment is deltaic, dominated by distributary channels and mouth bars.

Estimation of Initial Gas In-Place (IGIP) is important for gas field development. Well testing by recording bottom-hole pressure to conduct Pressure Transient Analysis (PTA) should not be limited to classical approach of determining permeability and skin parameters. Moreover, integration of time-lapse PTA can be very useful to reduce uncertainty of IGIP estimation as well as to access reservoir dimension when all reservoir boundaries are reached.

The advantage of time-lapse PTA with material balance model over classical P over Z (P/Z) method is capable to model reservoir dimension using either analytical or numerical. Other advantage is able to detect any transmissivity change due to fluid contact such as Gas Oil Contact (GOC) or Gas Water Contact (GWC). Estimation of IGIP using PTA from well testing is possible to be carried out before the well put on production or afterward, conversely P/Z method requires the well to be produced for quite some time to have pressure depletion.

DST survey in most of cases is carried out with limited duration in order to minimize operational cost related to rig time. Therefore conducting another well testing after well completion is useful when survey duration is more flexible as no time limitation associated to rig time. Furthermore well testing duration can be designed accordingly until all boundaries are reached in order IGIP can be estimated and reservoir dimension can be modeled accordingly.

This paper demonstrates the added value of time-lapse PTA in gas condensate reservoir. The integration of time-lapse well testing with the incorporation of one year of well production is considered as a good practice in reducing IGIP estimation and accessing reservoir dimension. Interference test was done to access reservoir connectivity between two wells where seismic interpretation shows different channel body. Based on connectivity between wells that penetrate channel reservoir 4d, material balance PoverZ (P/Z) to estimate Connected Gas In Place (CGIP)can be carried out accordingly.

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