Transient-rate analysis for long homogeneous and naturally fractured reservoir by the TDS technique

Normally, production data are analyzed by decline-curve fitting. However, analogous to pressure-transient analysis, the reciprocal flow rate and its derivative may be analyzed and interpreted for reservoir characterization purposes. In some cases, formation linear flow regime may be seen once the radial flow regime vanished. This flow regime is very important and can be presented in fractured well, horizontal wells and long reservoirs. Either pressure-transient analysis or rate-transient analysis may be affected by linear flow regime. For the case of production rate at constant well-flowing pressure, most of the analysis is conducted by decline-curve analysis and little attention has been given to rate-transient analysis. This paper presents the governing equations used for rate-transient analysis in elongated systems using characteristic points and “fingerprints” found on the log-log plot of reciprocal rate and reciprocal rate derivative, so analytical expressions were developed to determine reservoir parameters, following the philosophy of the TDS Technique. It allows for the estimation of reservoir permeability, reservoir width and geometrical skin factors. If the test is long enough, reservoir drainage area, well position inside the reservoir and/or reservoir length can also be determined. The methodology was successfully verified by its application to synthetic cases.