International Journal of Mining Engineering and Mineral Processing 2013, 2(2): 24-33 DOI: 10.5923/j.mining.20130202.02 Prognosticating the Production Performance of Saturated Gas Drive Reservoir: A Theoretical Perspective P. A. Owusu 1,2,* , L. DeHua 2 , E. K. Nyantakyi 1,3 , R. D. Nagre 2,4 , J. K. Borkloe 1,3 , I. K. Frimpong 4,5 1 Department of Civil Engineering, Kumasi Polytechnic, Kumasi, 00233, Ghana 2 College of Petroleum Engineering, Yangtze University, Wuhan, 430100, China 3 College of Geosciences, Yangtze University, Wuhan, 430100, China 4 Department of Chemical Engineering, Kumasi Polytechnic, Kumasi, 00233, Ghana 5 College of Geophysics, Yangtze University, Wuhan, 430100, China Abstract Saturated gas drive reservoirs are characterized by rapid and continuous decline of reservoir pressure. The resultant effect of this phenomenon is the early decline of reservoir performance at the primary stage of the life of the reservoir. The recovery of hydrocarbon from this type of reservoir through the conventional lifting (spontaneous production) is inefficient and uneconomic due to its least recovery efficiency leading to significant amount of residual oil. The Muskats model was used to analyze solution-gas drive reservoir and predict its primary oil recovery. The inflow performance of the reservoir was analyzed through the Fetkovich model. Outflow performance of various tubing sizes such as 2”, 2.5”, 3” and 4” was analyzed. The future performance of reservoir is forecasted in the three stages: the first one is to predict cumulative hydrocarbon production as a function of declining reservoir pressure, the second stage is time-production phase, and the third stage of prediction is the time-pressure phase. From the inflow performance relationship IPR analysis the maximum inflow rate obtainable is 1710bpd with outflow rate of 1200bdp. The flow capacity near the abandonment reaches 77bpd at about 15925days with cumulative oil produced as 7M Mstb. Keywords Solution Gas Drive, Recovery, Inflow Performance, Outflow Performance, Tubing String 1. Introduction Saturated gas drive is one of the depletion drive reservoirs in which the principal drive mechanism is the expansion of the oil and its originally dissolved gas as well as the associated pore space. The increase in fluid volumes during the process is equivalent to the production. As pressure is reduced rapidly and continuously in this type of reservoir remarked by[1], oil expands due to compressibility and eventually gas comes out of solution from the oil as the bubble point pressure of the fluid is reached. The expanding gas provides the force to drive the oil hence the term solution gas drive. It is sometimes called dissolved gas drive[2]. In solution gas drive reservoirs the initial condition is where the reservoir is under-saturated, i.e. above the bubble point. Production of fluids down to the bubble point is as a result of effective compressibility of the system. This part of the depletion drive may be termed compressibility drive. The low compressibility causes rapid pressure decline in this period and resulting low recovery. Below the bubble point, the expansion of the connate water and the rock * Corresponding author: princeappiahus@gmail.com (P. A. Owusu) Published online at http://journal.sapub.org/mining Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved compressibility are negligible hence as the oil phase contracts owing to the release of gas from solution, oil production therefore occurs as a result of expansion of the gas phase. When the gas saturation reaches the critical value, the free gas begins to flow. At fairly low gas saturations, the gas mobility, k g /u g , becomes large and the oil mobility, k o /u o , is small, resulting in high gas-oil ratios and in low oil recoveries, usually in the range of 5 to 25%[3]. The under recovery of this type of reservoirs make them the favorite for secondary recovery applications[4]. The behavior of the saturated gas drive makes the prediction of it recovery a complex one due to continuous changing of the gas and oil viscosities as well as the volume formation factors as a result of the pressure drops. Due to the inherent complexities, a number of simplifying assumptions are advanced to develop simple mathematical models. Several methods including Muskat’s method, Schilthius’ method, Tracy’s method and Tarner’s method have appeared in literature for predicting the recovery performance of this type of reservoirs based on rock and fluid properties The Muskat’s method gains a slight advantage over the others as seen in its wide application due to its simplicity. Furtherance to this, the analysis of the reservoir deliverability as to estimate the production rate at any given flowing bottom-hole pressure is a key to forecasting