Publications

The North Sumatra Offshore (NSO) field is a large gas field (OGIP - 2.7 TCF separator gas) that supplies gas to the P.T. Arun Liquefied Natural Gas (LNG) plant. The field came on-stream in 1999 and produces about 450 MMscfd currently from the Malacca limestone. The field has produced about 40% of the OGIP as of January 1, 2008, and the ultimate recovery is expected to be around 75%. Geomechanical testing of Malacca limestone cores indicated that the rock has high compressibility and suffers elastic and significant plastic deformation when mechanical stresses are increased. This paper discusses the development of a reservoir simulation model that incorporates the rock mechanical properties, fluid flow properties and surface facilities models to history match NSO production and reservoir pressure behavior. The impact of porosity and permeability reduction by plastic deformation on field production is also examined. Rock compaction is shown to be an important mechanism for matching the NSO production history and it provides part of the support needed to explain the higher than predicted reservoir pressures. Aquifer influx is shown to be the other support mechanism that is essential to matching the field performance. The model incorporates multirate and pressure buildup test results, and is updated on an annual basis. The simulation model is used to manage well and field production because large pressure drawdowns on the production wells may lead to payzone failure in openhole completions. The simulation results provide recommendations about altering well rates to optimize well drawdowns while meeting the overall field production rate requirements. The drawdown is also impacted by the skin around the wellbore. Pressure buildup tests were done in two wells to validate the simulation results that indicated that the wells may have positive skin. The pressure buildup analysis is presented in the paper, and integrated with the nodal analysis and simulation results.