This paper presents evaluations of acid-fracturing treatments. When fracture penetration and conductivity obtained from the analysis of both pressure-buildup and production data agree, then the combinations of fluid loss and retardation factor, which are required for geometry simulation to agree with the penetration, are determined. These parameters and other engineering assumptions can be used in the design of future treatments.
Evaluations of acid-fracturing treatments are usually based on a production increase or a comparison with other wells. These evaluations determine the relative success of materials and techniques compared with other materials and techniques. Pressure-transient analyses are sometimes used to determine fracture penetration and conductivity and formation transmissibility to evaluate a specific treatment. In this study, acid-fracturing treatments were evaluated to determine the specific acid-etched fracture penetration and conductivity achieved by treatments and to determine the utility of an acid-fracture geometry simulator in designing and evaluating treatments.
A numerical model, designed to simulate flow of a single-phase, slightly compressible fluid in a reservoir containing a heterogeneous, finite-capacity vertical fracture, was used to generate constant-pressure drawdown type curves for analyzing postfracture pressure-buildup data. An acid-fracture geometry model that couples hydraulic fracturing with acid-reaction kinetics was used to estimate the acid-etched penetration by simulating the actual treatment. Estimates of the etched penetration, fracture conductivity, and formation permeability were deemed satisfactory when these parameters agreed with both the post-treatment pressure-buildup and 6-month production data. The acid-fracture geometry simulation also was used to determine input parameter requirements necessary to obtain the penetration.