Transient Pressure Analysis in Composite Reservoirs with Rectangular Discontinuities

摘要

Numerical simulation was used to determine if the pseudosteady-state method presented by Eggenschwiler et al. (1980) can be applied to a long and narrow, rectangular swept-zone geometry. Two simulators were developed to generate transient pressure responses for a reservoir with a rectangular discontinuity. Cases with different width to length ratio (W/L) for the inner-zone were simulated for a mobility ratio of 200. The reservoir has a square geometry with closed outer boundaries. Sufficiently large distance was provided between the well and reservoir boundaries to prevent boundary effects during the time of interest. Results were analyzed with the pseudosteady-state method to find inner zone volumes. Results from the analysis indicate that pseudosteady-state flow does not exist for the inner zone for low W/L ratio cases. The curvature of the Cartesian plot of the pressure responses increases as W/L ratio decreases. For cases with W/L ratio below 0.4 the curvature becomes significant and many straight lines can be drawn through segments of the data. For cases with W/L ratio below 0.1, there is clearly no pseudosteady-state flow, and the Cartesian plot of pressure versus time is a continuous curve. It was found that swept-zone volume calculations are extremely sensitive to the slope of the pseudosteady-state straight line, if one exists. If the distance between the burning front and the well is not approximately equal in all directions, the slope will usually be too flat, and the volume calculated will be too large. A comparison between Cinco's type curve for a finite conductivity fracture and a case with an extremely low W/L ratio was also performed. The results show a favored match. However, for a rectangular burned zone to behave like a fracture at early time, the dimensions of the burned zone must be similar to that of a fracture. 22 refs., 45 figs., 5 tabs. (ERA citation 11:039679)