Increasing Lateral Coverage in Eagle Ford Horizontal Shale Completion

Abstract

Abstract A major challenge to efficiently developing a horizontal completion in shale is knowing what spacing and how many perforation clusters per stage will be optimal in effectively draining the reservoir. One of the major questions in developing the Eagle Ford shale was what spacing and lateral coverage will be optimal. A search for a case study revealed that no scientific study has addressed this concern. Industry practice has been based largely on available capital or best estimations. Hence the plan starting out was to carry out a case study of different lateral spacing and different perforation clusters per stage. The Eagle Ford shale play in South Texas is, in terms of development, in its infancy compared to other shale plays in North America. The Barnett shale, for example, has been commercially productive for over 15 years now, and the Haynesville shale has been commercially productive for over five years, whereas completion and commercial production of Eagle Ford is less than two years. Thus, there is the tendency to apply the methodology used in the older shale plays to Eagle Ford, which has different formation characteristics and mineralogy content. The first wells were completed in Eagle Ford with the typical 4,000 ft lateral length, four perforation clusters, and 300,000 - 350,000 lb of proppant per stage with a total of 16 stages. Radioactive tracers (antimony, scandium, and iridium) were used to tag the proppant, chemical tracers to mark the stage frac fluid, flow-through composite bridge plug was used to isolate the treated zone. After stimulating all the zones, plugs were drilled out and a Spectrascan tool was run in hole with coil tubing to log the lateral zone. Results from the tracer log on the first well show that most of the perforated zones were treated with the exception of the toe stage, which showed little or no stimulation. A close observation of the tracer log output shows that the treated lateral area (the area with tracer signature) was less than half of the entire lateral length. A linear count of the exact lateral length covered by the tracer mark compared to the entire lateral length revealed less than 36% coverage. This paper focuses on the changes that were made to the completion methodology in an effort to improve the stimulated lateral coverage, the effect of those changes on reservoir performance and improvement in the well productivity index. Details of the 100% improvement in stimulated lateral coverage that was obtained and the effect on productivity index are outlined in this paper. Introduction The Eagle Ford shale lies above the Buda limestone and is itself non-conformably overlain by the Austin chalk. Fig. 1 shows a stratigraphic column through Eagle Ford in South Texas. This cretaceous shale formation occurs over a laterally extensive area from Dimmit County in the west across the state to the eastern county of Lavaca and beyond.