Abstract

Fracture stimulations in Southern Oklahoma over the last few years, that utilize sand as proppant, have undergone a marked change toward more aggressive sand placement. Since initial development of 'modified fracturing treatments' in Carter County was reported in 1987, the number of jobs employing higher sand concentrations has continued to rise. This manifestation may be supported by post frac well performance data, which in Carter county indicates that the more aggressive or higher sand concentration treatment is the economically preferable stimulation. The progressive preferable stimulation. The progressive placement of higher sand concentrations has placement of higher sand concentrations has since become more frequent in other counties (e.g. Stephens), and producing formations (e.g. Tussy and Deese).

Background

The objectives of higher sand concentration applications in Southern Oklahoma have been to 1) improve permeability contrast and 2) enhance production of hydrocarbon reserves.

These goals have been successfully pursued by altering conventional treatment schedules to the 'modified' form. For example, in 1986 the typical job in the Hoxbar formation in Carter County, Oklahoma consisted of 15,000 gallons gelled or crosslinked fluid carrying 21,000 pounds of sand; today, the typical job consists of 10,500 gallons of crosslinked fluid carrying 42,000 pounds of sand. Respectively, applied sand concentrations have changed from 3 to 4 pounds per gallon in 1986 to a peak of 10 to 14 pounds per gallon today.

Proppant sizes and types have also evolved Proppant sizes and types have also evolved during this study. The first efforts at meeting the objectives employed larger sand sizes (e.g. 8–12 mesh). Yet, with expanded usage and time, 12–20 and 16–30 mesh sands have predominated. During early high sand concentration or 'modified' treatments using 8–12 mesh sand, screenouts limited the maximum proppant concentration to near 9 pounds per gallon. Today, refinement of pounds per gallon. Today, refinement of procedure and use of slightly smaller sands procedure and use of slightly smaller sands (e.g. 12–20 and 16–30 mesh) have made screenouts infrequent. Since Hickory and Ottawa type sands are normally used, resin coated sand sees minimal application.

Sand scheduling has also been important in meeting these objectives. Conventional work only provided fracture concentrations of 1 pound per square foot. Higher sand pound per square foot. Higher sand concentrations were needed to improve management of permeability damage effects (e.g. gel residue). Therefore, 'modified' treatments sought to maximize near wellbore sand concentrations in order to achieve superior fracture conductivity. The HSC or 'modified' job allows one to obtain a sand concentration equal to or greater than 2 pounds per square foot in the fracture. Present treatment designs, though not always at the HSC level, continue to pursue the highest plateau of propped fracture conductivity. propped fracture conductivity. P. 367

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