Decline Curve Analysis and Material Balance, as Methods for Estimating Reserves (A Case Study of D4 and E1 Fields)

Reserve estimation entails the interpretation of geologic and/ or quantitative calculation of the petro physical data, PVT(Pressure, Volume, and Temperature), and production histories of the reservoir to estimate the reserve¹. Reserve estimation using Decline Curve Analysis andMaterial Balance andattempts to answer the question of reserve evaluation based on performance trend. Various techniques have been developed for computing reserve².This study therefore focused on comparing Decline Curve Analysis and Material Balance using two fields as a case study. These are D₄ Sand Guico field, and the Eleke (E1) field. Particular emphasis was laid on the determination of decline rate from the graph of production rate versus cumulative production which was also used to obtain the maximum produced oil and consequently the stock tank oil initially in place (STOIIP) when the decline curve analysis was used.

Since the two reserves used are combination drives, the graph of the variables plotted against each other gave a slope U, known as the reservoir constant and the stock tank oil initially in place as the intercept when the material balance approach was used³.