This paper illustrates a process that allowed the operator to optimize production by placing large concentrations of proppant in the Morrow Sandstone in the North Texas Panhandle. This process first consisted of analyzing data and results from previous Morrow fracture stimulations within the study area, but it soon proressed to optimizing pad volume percentage, proppant grade, perforation scheme, frac fluid selection, and other critical factors over a four-well stimulation project. Initial efforts placed 8 lbm/gal of proppant; by the end of the project, 19.8 lbm/gal were being placed. Stimulation practices developed through this continual improvement process provided more cost-effective results.
This paper illustrates the challenge to place extreme concentrations of proppant in face of a high leakoff environment. This process required the use of an advanced, real-time, three-dimensional (3D) frac model to monitor prefrac calibrations and, in some cases, redesign the treatment to accommodate the leakoff field. Fracture stimulation quality control played a key role in these efforts.
The Morrowan Series in the western Anadarko Basin is commonly divided into the Upper Morrow and Lower Morrow formations. Production from both formations is from relatively clean, porous sandstones that comprise some of the most prolific producing gas reservoirs in the Texas and Oklahoma panhandles. Average initial production rates are 3 MMscf/D, with ranges from 0.1 MMscf/D to 21 MMscf/D. To date, the average gas recovery per well is 1.5 Bcf, with ranges between 0.1 Bcf to 8 Bcf. All Morrow wells within the study area are less than 15 years old, and 56% have produced for less than 5 years. These high initial rates are possible with average permeabilities between 5 to 5 md.
The inherent dry-hole risk of both formations can be attributed to the discontinuous nature of Morrow sand deposition. Lower Morrow sands are generally marine barrier/offshore sands deposited parallel to paleo shoreline trends. Within the study area of NE Sherman and NW Hansford Counties (Fig. 1), production typically occurs only at the updip termini of these sands. Upper Morrow sands are fluvial.1 These sands are deposited as discrete point bars within a broader valley system, resulting in a semilinear trend of segregated reservoirs. Only 34% of the Morrow exploration and development tests in the study area encountered productive Morrow.
Morrow fracture stimulation technology has grown dramatically over the past 15 years. In the early 1980's, fracturing jobs were conducted with gelled 3% acid and sand concentrations that rarely exceeded 1.5 lbm/gal. Energized fracturing jobs with N2 and CO2 foams, then became the norm, even in nondepleted wells, because of the nondamaging nature of these fluids. Job schedules were more aggressive, but sand concentrations rarely exceeded 4 lbm/gal.