These innovative, field-proven systems allow for exact placement of stimulation treatments in one continuous pumping operation. Once the stimulation operation is complete, the well can be immediately flowed back and production brought online.
While they are primarily used for horizontal wells, StackFRAC systems are also frequently used in open hole vertical wells to exploit stacked pay zones. For example, an operator working in the Permian Basin of west Texas, USA was targeting the layered combination of the Wolfberry and Bone Spring formations. This unconventional trend is a mix of fine sandstone and siltstone interbedded with various shale and carbonate layers that act as barriers to fracture growth, making well completions a challenge. The operator wanted to effectively complete these formations while keeping costs low. A horizontal technique was not viable due to the thickness of the pay zone (300 to 460 m) and multiple shale and carbonate barriers. Standard “plug and perf” stimulation methods were costly and time consuming, so the operator was exploring other completion options. The focus was on exploiting the higher porosity and permeability of the sandstone layers, as well as any natural fractures present.
The operator chose to run the Packers Plus StackFRAC systems in open hole vertical wells to maximize their total pay zone. The 11-stage systems were run to a total depth of 3,600 m with an average stage spacing of just over 30 m. The tight spacing was required to effectively stimulate the entire pay zone and help to overcome the natural barriers of the formation. The stimulation was a combination of slickwater and crosslinked fluid.
The vertical well completion design using the StackFRAC system was a success. The open hole completion allowed for contact with the entire length of the wellbore. On average, it took 21 hours to stimulate the 11 stages in each well. Of those 21 hours, 16 – 18 hours were spent pumping, the rest was down-time due to repairs of surface equipment. With the plug and perf method, there would have been a minimum of an additional 15 hours added to the stimulation time due to wireline rig up and rig down and wireline trip time in and out of the hole.
The Packers Plus StackFRAC system has helped achieve time and cost savings in addition to higher production volumes compared to the standard plug and perf offset wells. As a result of the various benefits realized, the operator plans to continue using the StackFRAC system in their Permian Basin wells.