Dedy Irawan, Doddy Abdassah, Zuher Syihab, Ratnayu Sitaresmi

Petroleum Engineering Department, Institut Teknologi Bandung, Bandung, Indonesia.

Petroleum Engineering Department, UniversitasTrisakti, Jakarta, Indonesia.

Reserves estimation and classification in reservoirs are important step in the CBM field development. Estimation both parameters are depend on radius of investigation and radius of desorption. This paper propose semi analytical method for estimation of radius of investigation combining with radius of desorption. Desorption radius was estimated using cumulative gas production data. Cumulative water production data, fractional flow curve and sigmoid function are used as a concept of estimating water saturation distribution as a function of time and radius, and this concept was used to estimate radius of investigation. Numerical model was developed to verify proposed radius of desorption and radius of investigation calculation resulted from the analytical method. San Juan Basin coal reservoir properties data were used for conducting the understanding and the applicability of proposed method. It was successfully showed that this proposed method can simultaneously estimate the radius of desorption and the radius of investigation using gas & water production rate and cumulative data. The results from the proposed method was also compared with the numerical reservoir simulation method and the results are in very good agreement. Since time parameters were not utilized in this calculation, makes this method is very simple for the practical purposes.