Abstract
This paper describes field examples of fracture optimization that are based on the after-closure pressure decline period following a proppant-free injection. The primary benefit from these applications is the determination of reservoir transmissibility that is central to specifying the fracture length and conductivity for optimizing field-development economics.
The transmissibility is obtained from the after-closure pseudo-radial flow period. In the examples this transmissibility is compared with that calculated from conventional well testing. In one example, the well-test derived fracture half length is compared to the optimized length predicted from a fracturing simulator. Simulated versus actual production results are also compared.
The after-fracture closure period of an unpropped fracture injection potentially contains the reservoir pseudo-linear flow and pseudo-radial flow periods. Analysis of the linear-flow period enhances the standard calibration analysis of the pre-closure period (i.e., mini-frac analysis). One enhancement is the potential determination of spurt loss that can not be obtained from the pre-closure decline because spurt loss ends as the fracture extension stops. Another enhancement is the reservoir behavior's perspective of closure time and fracture's length that permits validating the values of these parameters from the pre-closure analysis. This definition of length is obtained from combining the linear and radial flow analyses.
The field examples are for a moderate permeability, normally pressured, dry-gas Morrow sandstone reservoir located in Hemphill County of the Texas panhandle. The selected testing sequence, and synergy of information from independent pre-frac tests, are reviewed as well as operational and theoretical constraints. A logical application procedure is developed for general field use in similar environments.
