DERIV - A COMPUTER-PROGRAM FOR CALCULATING PRESSURE DERIVATIVES FOR USE IN HYDRAULIC TEST ANALYSIS

Hydrologic test analysis based on the derivative of pressure (i.e., ra te of pressure change) with respect to the natural logarithm of time h as been shown to significantly improve the diagnostic and quantitative analysis of slug and constant-rate pumping tests. The improvement in test analysis is attributed to the sensitivity of the derivative to sm all variations in the pressure change that occurs during testing, whic h would otherwise be less obvious with standard pressure change versus time analysis. The sensitivity of the pressure derivative to pressure change facilitates its use in identifying the effects of wellbore sto rage, boundaries, and establishment of radial flow conditions on the t est. DERIV is a program for converting slug and pumping test data and associated type curves to derivative format. The program has features that permit the smoothing of noisy test data, accounts for pressure de rivative end-effects, and can be used to convert slug test data to equ ivalent pumping test responses. Test examples that demonstrate the use of pressure derivatives also are provided.