Material-Balance-Time During Linear and Radial Flow

Abstract

Production data generally consists of variable rate and variable flowing pressure. It is convenient to be able to use reservoir models that assume a constant flow rate, since these solutions have been previously derived in the well testing literature. Thus, it is necessary to have a time function capable of converting general production conditions into the equivalent constant rate solution. Blasingame 1 , and later Agarwal et al 2 have shown that Material-Balance-Time provides an exact transformation of constant pressure data to constant rate type curves, during the boundary dominated flow regime. It also yields a reasonable approximation during radial flow, and when rate and/or pressure vary smoothly. Poe 3 has investigated the effectiveness of using material-balancetime for other transient flow regimes using the constant pressure solution, rather than the constant rate solution as a base model. The objectives of this paper are twofold. Firstly, it serves to investigate the applicability of materialbalance-time during the linear flow regime (fracture flow), where the difference between the constant rate and constant pressure solutions is more pronounced. Further to this, material-balance-time correction factors are quantified for both radial and linear transient flow regimes (this has not previously been done using the constant rate solution as the base model). Secondly, it serves to illustrate by synthetic and field examples, a comparison of material-balance-time against the logarithmic superposition time function, to determine under what circumstances material-balance-time errors significantly influence rate transient interpretation, in practice.