The key challenge for the US shale industry is to continue improving productivity per well, as illustrated repeatedly in our research. Hence, this short note reviews an advance in fracturing fluids, which has been patented by BP. Diverter compositions are optimised across successive pressurization cycles, to create dendritic fracture geometries, which will enhance stimulated rock volumes.
BP has patented a novel regime of fracturing fluids, which can be deployed across multiple pressurization sequences in its shale completions. The first sequence contains permanent diverting agents, introduced to create bi-wing and large fractures, then flowed back. The second fluid contains temporary, near-field diverting agents, which will dissolve in situ, usually within 24-72 hours, to expand the fracture network. Similarly, the third fluid contains temporary, far-field diverting agents.
The purpose of this completion design is to create dendritic fracture geometries. The diverting agents prevent fracturing fluids from leaking into the formation, so that primary, then secondary, then tertiary fracture networks can be created independently, each improving reservoir fluid conductivity (chart below).
The approach is data-driven. The formation of new fractures, with increasingly dendritic geometries, can be inferred from a linear slope between instantaneous shut in pressures on successive pressurization cycles. The fracturing fluids’ composition is also said to be determined based on Instantaneous Shut in Pressures, in-situ stress calculations and flowback volumes.
The permanent diverting agents may comprise mesh proppant, walnut hulls, large grain size proppants or particulates, such as polylactic acid, benzoic acid flakes, rock salt, calcium carbonate pellets. Small mesh size is envisaged (40-70 to 100 mesh), with low concentrations (0-0.1 lb/gal) to mitigate the risk of screen-outs.
The temporary diverting agents are not specifically disclosed in the patent, but are intended to dissolve in response to temperature, salinity, pH or other parameters. They may be pumped alongside proppant or standalone.
The patent is increasing evidence that Oil Majors are now innovating at the cutting edge of shale, in order to drive productivities higher. For a review of which companies screen as having the most advanced shale technologies, from the patent literature, please see our recent note, Patent Leaders.
Source: Montgomery, R., Hines, C. & Reyna, A. (2018). Hydraulic Fracturing Systems and Methods. BP Patent US2018202274