Production in the Appalachian Basin comes primarily from "tight" gas and oil sands of the Devonian and Silurian period. The primary target in Northwestern Pennsylvania and Southwestern New York is the Lower Silurian Medina Formation. Nearly all of these wells are stimulated by hydraulic fracture treatment. Proper of these wells is critical for economic results; therefore, knowledge of reservoir rock properties to enhance the completion comes increasingly important.
For improved completion design, measurements of rock mechanical properties need to be obtained. This can be accomplished either with a mini-frac or the use of log values. The optimized completion treatment despite would use these properties to accurately determine many important variables including perforation selection transport fluid type and viscosity, treatment volume and pumping rate, and proppant type and amount (all of which can be related to closure stress). These factors can be determined using the FracHite* Log output of gross fracture height, closure stress gradient, and treatment pressures.
This paper will deal with the application of log-derived parameters in modifying completion design strategy in the Medina formation. These modified completions will be compared with the "cookbook" completions as well as the production results of several wells treated with and without these vital parameters.
This lower Silurian Medina Sandstone Group is the target of most recent drilling activity in New York and Northwest Pennsylvania and 95% of the wells drilled are productive. The Medina is a fine to very fine-grained, interbedded sandstone which blankets this area (Fig. 1). The Medina formation is subdivided into two units, the Grims by formation overlying the Whirlpool formation. However, the Medina is low in intergranular porosity (6–8% and permeability (less than 0.1 millidarcy). Therefore, due to the very low permeability wells drilled to the Medina must be fracture stimulated. After stimulation, low but stable production rates can be obtained. Many Medina wells are capable of producing at steady rates for up to 20 years.
With the current oil and gas prices the process of completion design takes on added importance since the maximum productivity of the well is dependent upon completion design. The more efficient the completion, the faster the return on investment, and hydraulic fracture stimulation is the most critical step in the completion design of a Medina well.
To achieve the desired results, widely varying techniques of hydraulic fracture have been employed. These techniques range from cross-links and foams at very low injection rates (4–6 bbl/min), to linear gels at moderate rates (15-30 bbl/min) and to fiction reduced "slick water" at high rates (>40 bbl/min). Propping agents are almost exclusively frac sand although some operators utilize no propping agent for the high rate, slick water treatments. These treatments have evolved through trial and error investigation.
Treatment design is usually done by the "cookbook" with a standard treatment; however, small volume changes to that treatment often serve as the stimulation procedure for all conditions. Results of these treatments vary greatly, even within the operating area of an individual producer. Production optimization is impossible with proper identification and utilization of accurate parameters in the completion design process.
To optimize completion treatment design, measurements of rock mechanical properties need to obtained. With these properties in hand the completion design parameters can be accurately determined. This can be accomplished either with a mini-frac or the use of log-derived values. Through the use of logs many of these parameters can be determined in advance and a completion design based on the individual well can be planned.
The FracHite log provides many of the parameters needed for efficient completion design.