Abstract
Horizontal well drilling and multistage hydraulic fracturing are essential to economic recovery of unconventional tight/shale reservoirs. Multiple transverse fractures are ideally supposed to be perpendicular to the minimum stress direction, but slanted fractures might be seen in practice, which might bring a better connection between wellbore and fractures. However, for the same fracture half-length, the stimulated reservoir area might be less. Thus, the well performance of slanted faractures is full of uncertainty. Little research work is currently conducted on the horizontally slanted fracture scenario.
Our transient pressure analysis of horizontal well performance with slanted hydraulic fractures utilizes the concept of rate-normalized pressure and transient productivity index. The novel Fast Marching Method (FMM) is adopted to characterize the drainage volume evolution for multi-stage horizontal wells and validate the proposed methodology. Sensitivity studies contrast transient pressure behavior and productivity index for slanted fracture angles from 0 to 90 degrees, e.g. from longitudinal to transverse fracture angles. Additionally, transient pressure behavior and long term reservoir performance of horizontal well for different scenarios are investigated, such as reservoir anisotropy and different proppant allocation strategies under the constraints of given horizontal well spacing and total proppant mass.
Contrast to what we are usually expecting, results show that for the same fracture spacing, and the same total proppant mass, the well with slanted fractures will have a higher productivity index than that for strictly transverse fractures. Different from productivity index, the long term reservoir performance, however, turns out to play a different game, given specific horizontal well spacing and the same total proppant mass. Reservoir performance for horizontal well with slanted hydraulic fractures can be significantly improved by optimally allocating the proppant and designing hydraulic fracture placement strategies through this research.
