Resolving Created, Propped, and Effective Hydraulic-Fracture Length

Abstract

Summary Recent advances in hydraulic-fracture-mapping technologies have provided a wealth of information on the created fracture length in numerous geologic settings. Before having such measurements, fracture length was estimated using "uncalibrated" fracture-propagation models, but there was significant uncertainty in the results that cascaded into subsequent production analyses. However, we also need to understand how the created fracture length relates to the location of proppant in the fracture and to the producing or effective length to evaluate well performance and improve stimulation designs. Unfortunately, the advanced fracture-mapping technologies that provide accurate measurements of the created fracture length cannot provide any insights (yet) into the propped and effective fracture lengths. Advanced production-data analyses (PDAs), pressure-transient testing, and/or numerical reservoir modeling are required to determine the effective fracture length. This paper begins with a comparison of the strengths, weaknesses, and limitations of fracture modeling, PDA, pressure-transient analysis (PTA), and numerical reservoir modeling to estimate effective fracture length and conductivity. This work also evaluates how the complexities (in the hydraulic fracture) associated with non-Darcy flow, multiphase flow, and complex fracture geometries affect the results from the various techniques. This work documents the significant differences in "effective" fracture length that, in many cases, can result from each technique and how these uncertainties can impact fracture treatment designs and field-development decisions. The paper concludes with several field case histories that illustrate the integration of multiple technologies to determine the created, propped, and effective fracture length. The case histories illustrate the dramatic differences in created and effective fracture length that can occur in some reservoirs, while also showing that in some cases, effective fracture lengths can be very similar to the created length (and quite long). Integrating the results from multiple diagnostic techniques in a consistent and coherent manner can provide significant insights into created, propped, and effective fracture length that are otherwise unattainable from each technique alone.