Fairchild and Wood documented the benefit of refracturing gas storage wells in Ohio. Early treatments utilized 5000 to 45,000 lbs of 20/40 sand, with 25% pad and 2-3 lb/gal concentration. A refrac accepted 40,000 lb of 20/40 sand with concentrations up to 8 lb/gal. Flow testing showed post-frac deliverability doubled, and was over 187% higher than any previous treatment.
This paper presents a field case study on the application of advanced stimulation technologies (AST) to the East Ohio Gas (EOG) Stark-Summit Gas Storage Field, Clinton Formation, near North Canton, Ohio. The study demonstrates benefits in two ways: (1) increased deliverability; and (2) improved restimulation candidate selection. Using 3-D hydraulic fracture modeling and reservoir simulation, one of the actual (AST) treatments pumped during the study was compared to the typical 75-quality nitrogen foam treatment used in the 1996 restimulation program. This comparison showed that the new treatment improved proppant placement and fracture conductivity. Over a 150 day withdrawal cycle this increases the cumulative gas production by 29,900 Mscf and improves initial gas rates by 30%. In addition, actual flow test data showed that post-fracture deliverability was more than doubled over pre-fracture values, and was 187% higher than any previous post-fracture results in the study well.
The case study also demonstrated the importance of proper restimulation candidate selection. By using improved techniques for pre-treatment flow test evaluation, better estimates of existing permeability and current effective fracture half-length can be determined. Identifying wells with little potential for increased deliverability due to extremely high permeability or an existing effective hydraulic fracture prevents these wells from being restimulated which results in cost savings. If these wells are not properly identified, up to $20,000 can be spent on a restimulation treatment that has little chance of significantly improving deliverability. In addition, better estimates of permeability will enable hydraulic fracture treatments to be designed and optimized on an individual well basis.
To aid in the optimization of hydraulic fracture candidate selection, design, execution, and evaluation, the following technologies were used: one-point well test analysis, 3-D fracture design, reservoir simulation, real-time fracture treatment diagnostics, post-fracture welltest analysis, and isochronal flow test analysis. Two test wells were used to evaluate the application of the different technologies which led to significant changes in EOG's treatment schedules and proppant concentrations. The case study was conducted in cooperation with the Gas Research Institute and its Advanced Stimulation Technologies deployment program.
Author(s): Fairchild, N.R. Jr., Wood, D.D.
Paper Number: SPE 39220