This paper discusses possible explanations, based upon previous studies, for the hypothesis that multiple fractures at the borehole wall may be a common feature of the hydraulic fracturing process. It then uses field examples to show how we concluded that a type of low-concentration screenout common to three fields in Texas and Oklahoma was caused by multiple fractures. Next, it shows how we developed a completion that controls loss of the pad and slurry to multiple fractures. Finally, it discusses some of the implications of our experience for completion design in general. Since the symptoms of the low-concentration screenout have been documented in the literature by other authors and appear to be quite common, our design techniques should be effective in other areas as well.
The completion design combines unoriented, zero-degree-phased, big-hole perforations shot at low density; and small, high-concentration proppant slugs with clean spacer stages pumped very early in the treatment. These strategies were chosen (1) to limit the number of separate fractures that initiate from individual perforations, and (2) to screen out narrow fractures early in the treatment so that more width is developed in the remaining fracture(s). We have used these techniques to increase overall sand/fluid ratios (including the pad) from about 2.3 ppg (Ibm added per gal fluid) to over 8 ppg, on modestly-sized treatments up to 200,000 Ibm.