The two main objectives of using a hydraulic fracture model in coals are: (a) optimization of job design and placement, and (b) post-fracture diagnostics. Though certain limitations still exist, hydraulic fracture modeling in coals has undergone major advancements in the past decade. Pseudo or lumped three-dimensional (3-D) models have usually been employed to try and meet the objectives mentioned above. The effectiveness of using such models in coals has been very limited. Fully functional 3-D models are currently available in the industry and can be used to obtain better estimates of the fracture dimensions. This paper shows that a grid-oriented fully functional 3-D fracture simulator with shear decoupling can be especially useful in coals for post-fracture diagnostics if sufficient input data can be fixed from logs and Diagnostic Fracture Injection Tests (DFIT).

When problems occurred with placement of fracture treatments, especially in the upper Fruitland coals of a San Juan basin project, instead of experimenting with various ideas arbitrarily, technical evaluation using DFIT data and fracture modeling with a grid-oriented, fully functional 3-D fracture simulator, was used to pin-point the issues and address them accordingly. This paper will discuss the deficiencies of using 2-D and pseudo-3-D fracture models in coals and also will discuss the lessons learned from using a grid-oriented, fully functional 3-D fracture simulator in this project along with the successful implementation of the results developed from the modeling work.

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