The success of a hydraulic fracture treatment is greatly enhanced by control of the created fracture geometry. This problem is most serious if the boundary lithologies are not highly stressed as compared to the pay zone and do not form an effective barrier to upward migration. Reservoirs with this nature are common in many areas, including the Douglas Creek Arch, Green River Basin, Uintah Basin, San Juan Basin, and Central Alberta.
The Perforation Placement Optimization technique involves the determination of perforation locations such that the hydraulic fracture contact area within the pay zone is optimized. Where the upper boundary lithologies are not highly stressed as compared to the pay zone, the fracture will migrate predominantly upward into weak boundary lithologies. Where weak boundaries exist, the extent of the exposed fracture area that can be contained within the pay zone is strongly dependent on the location of the perforations and the gross height of the pay formation. Initiating the fracture below the pay sand (should lithology at the site be amenable to locating the perforations below the sand) can lead to greater fracture contact area within the pay sand and thus increased production. The work presented in the paper includes laboratory simulations performed on one meter cubic blocks, fracture design efforts, field implementation and transient pressure testing. The results of the laboratory tests helped in developing a model for optimizing perforation placement. This has been used in conjunction with a pseudo three dimensional fracture geometry and a pseudo two dimensional fluid flow hydraulic fracture model to design a field hydraulic fracture treatment. The treatment has been implemented in a well in the Douglas Creek Arch area, Colorado.
In-situ stress measurements in the well and special core testing on retrieved core material were performed to evaluate this well and the reservoir properties. In-situ stress distribution indicated the absence of stress barriers as expected. Reservoir engineering studies indicated that a significant increase in post-stimulation production can be expected by the use of perforation placement optimized hydraulic fracture treatment. The well was stimulated through perforations placed fifty feet below the pay zone and the created fracture was allowed to migrate upward into the pay zone. Post-stimulation transient pressure testing, fracturing fluid clean-up, and gas flow data indicate that the technique has been successfully applied.
This paper discusses the development, application, and evaluation of the modified hydraulic fracturing technique. This particular technique has been developed as part of a research program sponsored by the Gas Research Institute of Chicago and conducted by Terra Tek, Inc. of Salt Lake City and Chandler and Associates of Denver.