Pressure Buildup Techniques Applied to Identify Decreasing Fracture Stimulation Performance

Abstract

Fracture stimulation characteristics were measured and studied for changing behavior over a 6 month period using pressure buildup tests conducted on a Prudhoe Bay well. The suite of pressure tests included a pre-frac buildup, and two post-frac buildups at six month intervals following the fracture stimulation treatment. Pre-frac analysis exhibited radial composite characteristics consistent with other Prudhoe Bay well test analysis. Post-frac analysis showed the fracture length and conductivity to decrease over a six month period. Corroborating the well test results, production from this well decreased more rapidly than expected. Numerical simulation confirmed the results. Data acquisition pertinent to a successful well test analysis is discussed. Methodology A composite model (two concentric rings) with permeability increasing radially outward was used in the pre-frac test. A vertical fracture was incorporated into the composite model in the post-frac tests. If a pre-frac buildup was not conducted, the post-frac analysis would be highly speculative, because the pre-frac results were not a homogenous response. Fracture length and conductivity decreased between the two post-frac tests. Additionally, the fracture face skin increased slightly. As result, a component to the rapid decrease in production rate could be explained by the deterioration of the fracture length and conductivity. Conclusions1. Pressure buildup technology through effective design, application, and analysis, proved a viable method of monitoring fracture stimulation performance. 2. Accurate rate history is equally as important as the pressure-time data most generally associated with buildup analysis. 3. Analytical representation of a vertical fracture in a composite system can be adequately modeled with pseudo-boundaries. 235