Designing Completions in Horizontal Shale Gas Wells - Perforation Strategies

Abstract

Horizontal cased hole completions have become the accepted practice for completing wells in many shale gas plays. There has been a great deal of focus on how to optimize these completions. One of the most important, yet least discussed, concepts in horizontal shale completion optimization strategies is how to perforate to optimize for both placement efficiency of the hydraulic fracture treatment as well as production. Some of the perforation scheme characteristics that typically need consideration are as follows: The number of perforation clusters for each fracture stage The optimum number of perforations per cluster The distance between perforation clusters The length of each perforated interval Shot density, phasing and perforation charge type Optimal location to place the clusters Taking into account all of these considerations and using an optimized perforation strategy can be the difference between placing a fracture as per design or experiencing high treatment pressures throughout the stimulation treatment and prematurely aborting the job part way through. Even more importantly, properly engineered perforations can improve overall production by ensuring an equal fracture treatment through each perforation cluster as well as improving wellbore connectivity to the fracture. This paper looks at all these outlined aspects through a number of different means including a literature review, the use of simulation tools, and case studies from the Marcellus shale. Ultimately, a strategy for optimized perforations is presented with specific focus on shale gas horizontal wells in the Marcellus with further application to other shale gas plays.

A Literature Review of CO2, Natural Gas, and Water-Based Fluids for Enhanced Oil Recovery in Unconventional Reservoirs

“…This review will not delve into efforts toward enhanced gas recovery from unconventional gas reservoirs that produce little, if any, oil, − such as the fields in the Barnett, the Qusaiba in Saudi Arabia, and the Longmaxi in China. ,− Mechanical approaches to improving oil recovery such as improving the fracturing process, − optimizing wellbore geometry or spacing and stability, , improving perforation strategies, controlling proppant placement, modeling fracture patterns, developing choke management strategies, improving postfracturing operations and fluid cleanup, , refracturing, , production data analysis, and improving well monitoring technology, are also beyond the scope of this review.…”

Flow Isolation Tube for Milling and Sand Jet Perforating

“…Most technical papers reviewed in preparation of this paper agree on the methodology of using perforation clusters within the sections or stages of the frac that is being planned (Fan, 2010;Houston, 2010;Nwabuoku, 2011;Wutherich, 2012). The lengths of these clusters vary from two feet to five feet with the shot density, typically at 6 shots per foot (spf) and at 60 degree phasing.…”

“…Perforation design has clusters that are 1 to 5 feet long with 6 shots per foot on 60 degree spacing. Cluster spacing is typically 50 feet to 125 feet and stages are generally 2 to 4 per 1,000 feet of horizontal (Bartuska, 2012;Wutherich, 2012). • The Bakken Shale has formation depths that are 9,500 feet to 11,000 feet TVD with a thickness of 50 feet to 135 fee and temperatures in the 240° F range.…”

Re-fracturing Horizontal Shale Wells: Case History of a Woodford Shale Pilot Project

“…1.5 to 2.0 bpm at +/-200 psi per perforation in order for each cluster to receive adequate treatment coverage. The limited entry approach is a proven technique that originated in the early 1960's, to help improve treatment coverage in vertical wells and has since been adapted to use in horizontal well applications, see Lagrone et al (1963) and Wutherich et al (2012). Not all of the intervals achieved adequate limited entry characteristics, due to pressure constraints or formation effects, thus potentially leaving significant pay unstimulated.…”