Horizontal Well Completion, Stimulation Optimization, and Risk Mitigation

Abstract

Horizontal wells have become the industry standard for unconventional and tight formation gas reservoirs. Because these reservoirs have poorer quality pay, it takes a good, well-planned completion and fracture stimulation(s) to make an economic well. Even in a sweet spot in the unconventional and tight gas reservoir, good completion and stimulation practices are required; otherwise, a marginal or uneconomic well will result. But what are good completion and stimulation practices in horizontal wells? What are the objectives of horizontal wells and how do we relate the completion and stimulation(s) to achieving these goals? How many completions/stimulations do we need for best well performance and/or economics? How do we maximize the value from horizontal wells? When should a horizontal well be drilled longitudinally or transverse? These are just a few questions to be addressed in the subsequent paragraphs. This paper focuses on some of the key elements of well completions and stimulation practices as they apply to horizontal wells. Optimization studies will be shown and used to highlight the importance of lateral length, number of fractures, interfracture distance, fracture half-length, and fracture conductivity. These results will be used to discuss the various completion choices such as cased and cemented, open hole with external casing packers, and open hole "pump and pray" techniques. This paper will also address key risks to horizontal wells and develop risk mitigation strategies so that project economics can be maximized. In addition, a field case study will be shown to illustrate the application of these design, optimization, and risk mitigation strategies for horizontal wells in tight and unconventional gas reservoirs. This work provides insight for the completion and stimulation design engineers by: 1. developing well performance and economic objectives for horizontal wells and highlighting the incremental benefits of various completion and stimulation strategies, 2. establishing well performance and economic based criteria for drilling longitudinal or transverse horizontal wells, 3. integrating the reservoir objectives and geomechanic limitations into a horizontal well completion and stimulation strategy, and 4. identifying horizontal well completion and stimulation risks and risk mitigation strategies for pre-horizontal well planning purposes.

Unconventional gas reservoir evaluation: What do we have to consider?

“…We refer you to excellent recent summaries by King (2010), Cramer (2008), Britt and Smith (2009) and Mayerhofer et al (2008).…”

Fracture stimulation fundamentals

“…Fig. 4A shows a plot of Net Present Value versus the Number of Fractures as a function of lateral length for a tight gas reservoir with a permeability of 0.01 md (Britt and Smith, 2009). As shown, with one fracture in the horizontal well of this tight gas reservoir, there is marginal economic benefit of increased lateral length.…”

“…Much like the benefit of increased lateral length, however, the benefits of increased fracture half-length are sensitive to the fracturing costs. (Britt and Smith, 2009). B: The economic effect of fracture length (Britt and Smith, 2009).…”

Shale gas simulation considering natural fractures, gas desorption, and slippage flow effects using conventional modified model

“…The gas slippage effect is commonly defined by Klinkenberg slippage factor (Klinkenberg 1941;Britt and Smith 2009).…”

“…In addition, in tight gas reservoirs, there are significant incidences of natural complex mineralized or plugged fractures. Fracturing of horizontal wells with hybrid fluid or slick water (SWF) (Britt and Smith 2009) not only increases fracture formation contact areas by creating SRVs, but also reactivates natural fractures to some extent, which is vital to tight gas production (Ozkan et al 2009;Clarkson 2013).…”