A project was initiated in the Wolfcamp shale to reduce the operational complexity and costs associated with hydraulic fracturing. The goal was to use dissolvable diverter to increase fracturing stage lengths while maintaining an average cluster spacing similar to the current completion design without affecting well productivity. To ensure maximum effectiveness, a unique methodology was employed that uses reservoir properties along the lateral to create stage specific diverter strategies.
The methodology used to design the diverter strategies begins with understanding well heterogeneity along the lateral. Estimations of minimum in situ stress at each cluster were combined with estimates of pressure increases caused by stress shadow both from previous stages and between treatment clusters to determine fracture breakdown pressures along the lateral. This data was used to selectively segregate the clusters into those that would be treated before diversion and those that would be treated after diversion. Additionally, calculations including hoop stresses and perforation friction were used to ensure pumping pressures remained in a range that increased the probability that clusters designed to take fluid after diverter were not prematurely broken down during the initial pumping treatment.
This approach of engineered diversion was applied to three wells located in the Wolfcamp shale of the Midland Basin. The completion incorporated a designed stage length that averaged 315 ft with nine perforation clusters per stage using a single diversion drop. Typical well designs in this field contain stages that are 175 ft in length with five perforation clusters. Thus, this revised design constituted an eighty percent increase in stage length over conventional stage designs.
The goal of the treatment was to increase stage length without affecting production. During the treatment of the new engineered diverter stages, there was clear indication that after the first portion of the fracture was completed and diverter had seated on the perforations, the fluid was effectively diverted to virgin rock. This is a positive indication that the stage-specific diverter design was effective. Additionally, when comparing production between the three wells in this study and conventionally stimulated offset wells, there was no appreciable difference in production.
This case study represents one of the earliest applications of a fully engineered diversion strategy and will describe how lessons learned during this application can be applied to further improve economics and effectiveness of diverters in horizontal shale plays.