(589g) Maximizing Uniformity of Hydraulic Fracture Stimulation of Horizontal Wells through Stress Shadow Balancing and Limited Entry Methods

The combined practice of horizontal drilling and hydraulic fracturing has made production of petroleum resources from ulta-low permeability shale formations both technically feasible and economically viable. However, a major concern about ongoing development of shale reservoirs is a trend towards increasing development intensity in order to try to increase gas/oil production. That is, there can be a tendency towards solutions that entail more well pads, more water, more chemicals, more sand, and therefore more potential for negative environmental and community impacts. Reversing a trend towards increasing development intensity requires a focus on developing approaches that make the most of every well that is drilled, striving towards an industry that is more efficient in terms of gas/oil recovery from a given level of development activity. And, in fact, there ought to be substantial gains that can be made through efforts to make the most of every foot of every well because one thing is clear about the current technology of horizontal drilling and hydraulic fracturing: It is still achieving results that are far from optimal. Of particular concern is the fact that data from producing wells show a tendency for 1/3 or more of the drilled length of horizontal wells to be completely unproductive. A likely cause is that fluid that is injected with the intention of generating hydraulic fractures from all perforation clusters – the clusters of holes through the well casing that allow fluid exchange between the well and the reservoir - is instead diverted to only a portion of the clusters leaving many sections of the well unstimulated.

Thus motivated, here we present a numerical parametric study showing two methods for optimizing uniformity of stimulation through design of the clusters of perforation holes that are used as the entry points for fluid from the wellbore into the formation. We show that non-uniform perforation cluster locations combined with designing the entry friction associated with the perforation clusters (“limited entry”) can be optimized to produce the maximum surface area for an array of hydraulic fractures. Optimization is carried out using a reduced order, approximate simulator capable of carrying out an entire coupled simulation, which would normally take hours or days, in seconds to minutes on a desktop computer. Candidate designs are then tested using a fully-coupled, Planar 3D, multi-hydraulic fracture simulator that uses an Implicit Level Set Algorithm (ILSA). We find that for stages completed with 5 perforation clusters, optimizing the cluster spacing leads to over 70% increase in fracture surface area generated by the same injected volume. For uniform cluster spacing, optimal limited entry design alone is able to improve the fracture surface area by approximately 10%. When combined and optimized, improvements can approach a doubling of the fracture surface area leading to a potential for a similar order of increase in hydrocarbon recovery.