This paper presents an analytical derivation that constitutes a sound theoretical background for gas flow equation. This gas flow equation is based on a new pseudotime function which, unlike the computation of material balance pseudotime, is insensitive to time step-size and purely analytical. This new pseudotime function offers a simpler approach to handle viscosity-compressibility variations since viscosity-compressibility ratio is a function of cumulative production. Unique to the proposed approach is that the flowing material balance method utilizes pseudocumulative, which is not a function of material balance pseudotime. Currently, the analytical derivation given in the literature for gas flow equation involving material balance pseudotime has created the perception that material balance pseudotime is intuitive. An analytical derivation is given to show that material balance pseudotime function has sound theoretical basis. Presently, iterative scheme, algorithms and graphical techniques involving a number of plotting functions have been proposed to solve gas-in-place. This paper presents a direct approach to solve gas-in-place when early pseudosteady state line is observed. Additionally, a technique is given to validate computed initial-gas-in-place; thus initial-gas-in-place computed by any method can be verified with the proposed technique. The proposed analysis yields initial-gas-in-place, pseudosteady state constant and drainage area. Two simulated and one field published examples are presented to validate our proposed analysis.

This paper presents a method that can be used to analyze constant-rate drawdown tests to determine average reservoir pressure as a function of flowing time. The proposed method couples the pseudosteady state equation with its integral function to yield a unique plotting function that results in a zero slope (i.e., a constant value on the ordinate), which, based on the definition of stabilized flow equation, is equivalent to the difference between the average reservoir pressure and the bottom-hole flowing pressure. The average reservoir pressure history is, thus, obtained since the bottom-hole flowing pressure profile is known. As opposed to derivatives, the proposed approach yields smooth data; and is very diagnostic on the cartesian plot. Extension to gas wells is also considered. The significant contribution of this paper is that average reservoir pressure profile can directly be estimated using constant-rate drawdown test. Also, our proposed approach is based on a sound theoretical background. We demonstrate the validity of the proposed method with simulated and field data that are already published in the literature.

Appropriate selection of rheological models is important for hydraulic calculations of pressure loss prediction and hole cleaning efficiency of drilling fluids. Power law, Bingham-Plastic Herschel-Bulkley models are the conventional fluid models used in the oilfield. However, there are other models that have been proposed in literature which are under / or not utilized in the petroleum industry. The primary objective of this study is to recommend a rheological model that best-fits the rheological behaviour of xanthan gum based biopolymer drill-in fluids for hydraulic evaluations. Ten rheological models were evaluated in this study. These rheological models have been posed deterministically and due to the unrealistic nature these were replaced by statistical models, by adding an error (disturbance) term and making suitable assumptions about them. Rheological model parameters were estimated by least-square regression method. Models like Sisko and modified Sisko which are not conventional models in oil industry gave a good fit. Modified Sisko model which is a four parameter rheological model was selected as the best-fit model since it produced the least residual mean square. There is 95% certainty that the true best-fit curve lies within the confidence band of this function of interest.

We investigate, through a graphical representation of dimensionless pseudocumulative function, the possibility of using only the early time boundary-dominated flow (BDF) data to make an initial estimate of gas-in-place. In particular, we demonstrate that when viscosity-compressibility product ratio is plotted against fractional recovery on linear coordinates, an early straight line is observed during BDF regime. This phenomenon permits the dimensionless pseudocumulative function to be expressed as a quadratic function which, upon approximation, yields a linear function in terms of fractional recovery. This work thus demonstrates that the utilization of actual cumulative in gas flowing material balance yields two negative slopes Ϫ early time and late time BDF lines. As opposed to the late time BDF line, the early time BDF line yields a reasonable initial gas-in-place, and thus considerably reduces the number of timeconsuming iterations associated with computing material balance pseudotime function. Perhaps, the significant finding of this work is that it establishes that the approximate gas flowing material balance equation is strictly applicable to the early time BDF data. Simulated and field data for both single-and multi-well systems are presented to demonstrate the applicability of the proposed approach.