Frac-and-Pack Stimulation: Application, Design, and Field Experience

Abstract

Paper first presented at the 1993 SPE Annual Technical Conference and Exhibition held in Houston, Oct. 3-6. Combined with SPE 26563 and published in the Journal of Petroleum Technology, March 1994. Summary A relatively short, highly conductive fracture created in a reservoir of moderate to high permeability will breach near-wellbore damage, reduce the drawdown and near-wellbore flow velocity and stresses, and increase the effective wellbore radius. Fracturing treatments of this type have two stages:fracture created, terminated by tip screen out, and fracture inflation and packing. Such a two-stage treatment is the basis of a number of newwell-completion methods, collectively known as "frac-and-pack." This technique has been successfully applied, with a range of fracture sizes, to stimulate wells in various reservoirs worldwide. This paper discusses the criteria for selecting wells to be frac-and-packed. We show how a systematic study of the inflow performance can be used to assess the potential of frac-and-packed wells, to identify the controlling factors, and to optimize design parameters. We also show that fracture conductivity is often the key to successful treatment. This conductivity depends largely on proppant size; formation permeability damage around the created fracture has less effect. Appropriate allowance needs to be made for flow restrictions caused by the presence of the perforations, partial penetration, and non-Darcy effects. We describe the application of the overpressure-calibrated hydraulic fracture model in frac-and-pack treatment design, and discuss some operational considerations with reference to field examples. The full potential of this promising new completion method can be achieved only if the design is tailored to the individual well. This demands high-quality input data, which can be obtained only from a calibration test. This paper presents our strategy for frac-and-pack design, drawing on examples from field experience. We also point out several areas that the industry needs to address, such as the sizing of proppant in soft formations and the interaction between fracturing fluids and resin in resin-coated proppant. Introduction The idea of combining sand control and well stimulation in a single treatment was first practiced in Venezuela some 30 years ago. The treatment consisted of perforating the pay zone, then applying a small-scale fracturing treatment with a viscous crude (10 to 20 cp) and sand sizing to control formation sand. Ball sealers were used in long intervals to promote distribution across the entire section. A screen was washed down through the gravel remaining inside the casing after the fracture treatment, and additionals and was placed around the screen where necessary. This technique yielded relatively high production rates because of low skin and adequate sand control. This treatment was later extended to consist of a small, propped fracture designed to bypass the skin around wells completed in well-consolidated sands that were severely impaired. In this case, the screen was not run and the gravel was not topped up. A typical job for a 100-ft interval would consist of 500 to 800 bbl of crude oil (18 API) with some 40,000 lbm of 10- to 20-meshsand. This propped minifracture typically yielded a two- to three-fold increase in production rate. Though it received considerable publicity, to the best of our knowledge, the technique was never applied widely outside Venezuela. Nevertheless, the technology in this area has now developed to the point where the theoretical understanding of the processes involved has greatly improved, proven treatment design tools are available, and vastly improved mixing and pumping equipment has been developed for both gravel packing and propped hydraulic fracturing.