Improve Unconventional-Reservoir Completion and Stimulation Effectiveness

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 152839, ’Improving Completion and Stimulation Effectiveness in Unconventional Reservoirs - Field Results in the Eagle Ford Shale of North America,’ by C.D. Pope, SPE, Complete Shale, and Terry Palisch, SPE, and Pedro Saldungaray, SPE, Carbo Ceramics, prepared for the 2012 SPE/EAGE European Unconventional Resources Conference and Exhibition, Vienna, Austria, 20-22 March. The paper has not been peer reviewed. In unconventional reservoirs, project success is driven by the completion. Most shale wells have long horizontal wellbores completed with cemented or uncemented casing strings. Economical wells require large hydraulic-fracture treatments in multiple stages along the lateral. Several areas are critical for a successful completion, including casing size and pressure rating, wellhead selection, treatment design, perforation spacing and stages, linear vs. crosslinked fluid, and proppant selection. While no two resource plays are the same, these findings can be used as a guide in other unconventional plays. Introduction One of the more active shale plays in the United States is the Eagle Ford shale (EFS). Exploitation of the EFS has focused attention on the potential of liquid-rich unconventional plays. Past vertical completions proved to be inefficient and uneconomical. However, successful results in the Barnett and Haynesville shales encouraged a search for other shales that could be developed with similar horizontal-well completions and multistage-hydraulic-fracture stimulations. This play has been exploited almost entirely by the use of long horizontal wells. The rig count was less than 20 in 2009 but rose to more than 200 by the end of 2011. By the end of 2010, approximately 30 million BOE had been produced from approximately 600 wells. As of the writing of this paper (January 2012), approximately 1,800 horizontal wells had been completed in the EFS since activity began in 2008. Geologic and Reservoir Discussion The EFS is productive in a trend that appears to exceed 15,000 sq miles in south Texas. Production has been established at depths from 5,000 to 14,000 ft. The EFS ranges in thickness from 50 to 400 ft within the productive trend. The formation produces from dry-gas, wet-gas, volatile-oil, and nonvolatile-oil windows. Porosity ranges from 4 to 11%, and permeability ranges from 50 to 1,500 nanodarcies. The EFS is thought to be self-sourced in that the hydrocarbons are thermogenically sourced from the kerogen that is present. Therefore, the reservoir is overpressured and shallower portions of the EFS are less thermally mature with lower porosity. However, these lower- porosity areas are oil bearing, while the gas-bearing intervals are deeper, have higher porosity, and are overpressured. Reservoirs found between the shallower oil and deeper gas windows range from volatile oil to condensate-rich gas.