Reserve estimation is the process by which the economically recoverable hydrocarbons in a field, area, or region are evaluated quantitatively. It is the pre-requisite for the development and planning of a gas field, simultaneously it plays a vital role for predicting future production performance and formulating depletion scenarios.
The common techniques for reserve estimation are the material balance method, the production decline curve analysis & the volumetric reserve estimation. The material balance method is simply the law of conservation of mass, which not only estimates the gas initially in place (GIIP) and recoverable reserve but also provides insights on the reservoir drive mechanism. The decline curve analysis method, which is generally applied to single well, assumes that the future production will follow the past trends and uses the production data to fit an empirical rate/time decline equation to estimate GIIP in the drainage area of the well. Various decline type curves are also available that use analytical solutions of the diffusivity equation.
In this study both of methods and their modified forms, based on their applicability, are used to estimate the GIIP of the upper gas sand (UGS) and the middle gas sand (MGS) of a gas field in Bangladesh. The analysis suggested that the UGS might be under water drive. The results were compared and concurred with the volumetric estimates earlier made. The total reserve obtained from above mentioned methods for the producing gas sands was ranging from 1.7 to 1.855 TCF.
Contributors: Ahmed T, Akter F.
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