Advanced Stimulation Technologies Cut Costs and Increase Production in Medina Stimulation
Authors: Fairchild N.R. , Paugh Len 
Published: December 2007

This paper presents a stimulation case study in the Medina formation in northwest Pennsylvania. The study was conducted in the Mosiertown Field, which is operated by Lomak Petroleum, Inc. Several Advanced Stimulation Technologies (AST) were used to optimize fracture design and execution on six wells, as part of the Gas Research Institutes technology transfer program. Production analysis was performed on existing wells in the field to establish base line reservoir parameters. The base line reservoir parameters were then used in an economic model with current stimulation costs to determine the optimal fracture half-length. Once an optimal fracture length was determined, a treatment was designed that would theoretically generate the desired length. The design was then taken to the field and executed with the help of real-time hydraulic fracture modeling. Minifracs were conducted on each well and the real-time model was used to estimate closure stresses, fluid leakoff, permeability, and wellbore entry problems. These parameters were used to fine tune the fracture model and adjust pad volumes for each well. The real-time model was also used during the main treatment to assist in achieving fracture packoff and track the effects of proppant concentrations entering the formation. Post-fracture production analysis and direct production comparisons were used to determine the effectiveness of the stimulation treatments.

Drastic reductions in pad volumes and greatly increased sand concentrations cut total fluid volumes by 40%. The cost savings were estimated at $3,000 per well, which is approximately 3% of the total well cost. In addition, post- fracture cleanup times were reduced to 3 to 4 days compared to a week with previous treatments using larger fluid volumes, and past sand production problems were eliminated by obtaining a packed fracture. Six months of post-fracture production data were analyzed and showed that production had been significantly increased (45% - 90%) in the study wells as compared to offset wells.

Background

The Mosiertown Field is located in Crawford County, Pennsylvania. The primary target is the Medina Sandstone Group which lies at depths ranging from 3,800 to 4,400 ft. This field underwent initial development in the early to mid 1960's coinciding with the discovery and partial development of the Kastle and Indian Springs Fields. Mitchell Energy developed a large portion of the Mosiertown Field in the early to mid 1980's. Since 1982, this area has become increasingly active.

Production from the Medina Sandstone group is primarily stratigraphically controlled. The Grimsby Sandstone is the best pay interval with net pay thicknesses ranging from 5 to 35 ft. Porosity on openhole logs ranges from a low of 7% to 16%. Typical permeabilities range from 0.001 md to 0.1 md. classifying the formation as a tight gas sand. Additional reservoir potential is encountered in the Cabot Head and Whirlpool intervals.

Stimulation of the reservoir was always difficult. Screen-outs were observed at sand concentration above 4 ppg and proppant flowback during production was a problem. Mitchell Energy attempted a variety of stimulation treatments, ranging from foams to crosslinked gels. In 1994, Lomak continued to stimulate with a linear gel, but screen-outs and proppant production persisted. Typical treatments used 45,000 gals of total fluid which included a 500 gal. acid balloff, 14,000 gal pad, 1,100 sks of 20/40 sand, and sand concentrations of 4 to 6 ppg. The majority of the treatment was pumped at 4 ppg using a 20–30 lb linear gel, with higher concentrations being placed at the end of the treatment. Because of the thin fluid, large pad volumes and low sand concentrations, fracture modeling indicated that proppant may not be effectively placed over the pay interval.

In 1995, Lomak entered the Gas Research Institute's "R&D Wells for Technology Transfer" program through a coordinating consultant (Eastern Reservoir Services). The program was designed to introduce the producer to AST technologies that had previously been developed through GRI. P. 259