Horizontal Wells in Tight Gas Sands: Risk Management To Maximize Success

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 110067, "Horizontal Wells in Tight Gas Sands - A Methodology For Risk Management To Maximize Success," by Jason Baihly, SPE, Dee Grant, SPE, Li Fan, SPE, and Suhas Bodwadkar, SPE, Schlumberger, originally prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11-14 October. The paper has not been peer reviewed. Successful applications of horizontal wells have been limited to high-permeability reservoirs and unconventional formations such as coal, chalk, and shale. Horizontal wells are commonly two to four times more expensive to drill and complete than offset vertical wells, yet theoretically are capable of as much as three to five times the production. However, research shows that in practice, many of these wells produce only 10 to 30% more than offset vertical wells. The full-length paper presents a detailed methodology to identify, understand, and manage risk associated with horizontal wells drilled in tight gas sandstone reservoirs. Introduction Horizontal wells have had great success in high-permeability oil sands, unconventional gas shales, and carbonates. With advances in drilling and completion technologies, there has been a recent trend in North America to drill and complete horizontal wells in tight gas sandstones. In the full-length paper, tight rock is defined as sandstone with permeability less than 0.1 md. Whenever the gas price has been strong in North America, operators tend to attempt more-innovative and inherently riskier investments in natural-gas plays that include new-formation plays, varied drilling techniques, and experimental completion methods. With the current active climate and favorable gas price, increasing emphasis is being placed by exploration-and-production companies on getting as much gas out of the reservoir as quickly as possible, while minimizing cost. Horizontal wells allow operators to increase gas production of a well by exposing more of the reservoir to fracture stimulation. This increases the likelihood that a horizontal well can produce more than its offset vertical counterparts. The key is that the production increase must more than make up for the cost increase associated with the horizontal well. The challenge is identifying and mitigating risks in tight gas sandstone horizontal wells. Methodology The full-length paper discusses each phase of the methodology that can be used to minimize the risk and maximize the success of horizontal completions in tight gas sandstones. The sections include the reservoir model, planning, drilling, completion, and production. In the full-length paper, throughout the various phases there are some discussions about how one or more aspects of a certain phase will affect the design and success of the overall horizontal well or affect other phase aspects that occur subsequently. This methodology is by no means a linear progression; it is circular, so that all aspects of each phase have the greatest amount of input to design and risk mitigation of horizontal completions in tight gas sandstones.