Hydraulic Fracture Modeling and Design - A Perspective on How things have Changed from Conventional to Unconventional Reservoirs

Abstract

AbstractIn hydraulic fracture stimulation of conventional reservoirs (e.g. tight gas and deepwater unconsolidated sands), the use of sophisticated design models is almost indispensable. Typically, each hydraulic fracture is sequentially pumped and executed from near vertical wellbores. It is well understood that the optimum post-fracture well productivity is directly linked to hydraulic fracture dimensionless conductivity, which is governed largely by propped fracture length and width. From an engineering and operation execution point-of-view, the goal is to pump into the fracture and pack it with the desired volume of proppant without encountering premature ‘screen-out’. Therefore, the prediction of fracture geometry, the selection of ‘pad’ volume and proppant pumping schedule become critical for propped fracture design. In practice, a wide range of models have been deployed successfully. However, such considerations do not appear to be important for unconventional resources where multiple fractures are pumped from a long horizontal well. In fact, multi-frac horizontal well technology has advanced through field trials and experimentation, often without much help from modeling or understanding of multiple-fracture mechanics. This begs the questions of what areas of research and model design parameters should we focus on? Can we avoid the details while dealing with the big picture such as fracture spacing, horizontal well length/direction, the well's landing depth, and their impact on cost and production?This extended abstract revisits the motivation and well-accepted design approach for hydraulic fracturing in conventional reservoirs and some of the challenges facing hydraulic fracturing design in unconventional reservoirs. Practical first-pass design considerations based on geomechanics for fracture spacing and horizontal well landing depth selection are outlined.