Technical Paper: First Laboratory Perforating Tests in Coal Show Lower-Than-Expected Penetration

Society: SPE
Paper Number: 102309
Presentation Date: 2006
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Worldwide Coal Bed Methane (CBM) resources are huge, estimated at 3,000 to 9,000 Tcf. The worldwide production from CBM is dominated by US production of 1.6 Bcf/year, where an estimated 20,000 wells are in production from CBM reservoirs. Wyoming’s Powder River Basin (PRB) alone has 12,000 wells in production, with an estimated 50,000 more wells to be drilled in the next 10-15 years. The production rate from CBM reservoirs is low, perhaps 50-100 mcf/day. Various completion methods are being evaluated and new technologies are being developed with the aim of increasing production rates.

Considering this interest and activity level, there has been very little attention paid to the CBM completion fundamentals. Perforating is a critical part of this process, especially considering the PRB development migration from single-coal open-hole completions into multi-zone cased-hole completions Whereas the industry has substantial knowledge of perforating characteristics in sandstones and, to a lesser extent, carbonates, almost nothing is known about perforating in coal. Predictions of perforation characteristics, such as depth of penetration, are based on correlations developed for sandstones.

This paper will describe the first known laboratory-testing program to investigate shaped charge penetration in coal targets. We will describe mechanical properties of the coals tested,and penetration results for different shaped charges (of different designs), shot at various stress conditions. CT scan and cutaway imaging of the perforation tunnels will also be discussed. Tests were conducted under dry and saturated conditions.

The preliminary experiments reported here indicate that shaped charge penetration in coal is significantly less than expected, considering the target’s density and strength. The authors will provide insight into what may be the reasons for these unexpected results and recommend a path forward for shaped charge testing, designs, predictive tools, and how to optimize CBM completions.

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