Publications

The classical Material Balance (P/Z) plot requires fully shut-in built-up reservoir pressure (Pr) for its calculation by generating static Pr as a function of cumulative gas production (Gp). Shut-in the well only for Pr data acquisition is impractical and creates several issues such as risk of production loss and production disturbance. Mattar & McNeil (1997) introduced Flowing Material Balance approach for gas deliverability monitoring and reserves estimation based on surface well flowing parameter by creating parallel line through the initial Pr to estimate Initial-Gas-In-Place (IGIP). The method is practical for qualitative purpose, but any dynamic behavior of the well will be challenging. Improved model is presented, a Coupled Material Balance - Nodal Analysis approach for gas deliverability monitoring and reserves quantification of connected gas in place volume (CGIP). Initial Pr as a known variable then extended by the decline of Pr as a function of Gp and improved by performing “flowing mode” Nodal Analysis, converting bottom hole flowing pressure from wellhead flowing pressure to determine estimated Pr. Pr uncertainty and its depletion could be identified by sensitivity analysis, such as inflow productivity and water encroachment evolution. This approach has been applied for well T-32 of Tunu field, a mature field in Mahakam, to perform as single-reservoir gas deliverability monitoring by using only flowing parameter data. The “flowing” mode of Pr estimation with actual Gp, gives good performance of CGIP estimation without any shut-in activities, since this well is one of the big gas producer. This model also handled the dynamic activities of operation: well movement, production curtailment and improvement. The unknown variable of continuous water encroachment is also handled by wellbore temperature model which justified with actual data. This improved model could be considered as an alternative approach for gas reserves quantification and gives advantage for production strategy.