This paper summarizes the results of a cleanout study performed on six Devonian Shale wells in southwestern West Virginia. This study was part of a joint Columbia Gas System Service Corporation (CGSSC), Columbia Natural Resources (CNR), and Gas Research Institute (GRI) project which involved 'cleaning out' shale rock debris from several old, natural, openhole Devonian Shale wells for the purpose of evaluating Devonian Shale production mechanisms. Based on well test analysis and four years of production data, it appears the cleanout procedure is economically attractive for increasing production from these types of wells.
Six wells in Mingo, Wayne, and Logan Counties, WV were selected as candidates for study. Using a cable tool rig, Columbia found the Devonian Shale openhole sections in these wells filled up and bridged off with shale rock debris. The debris was removed with a bailer, but some tool sticking problems were encountered. Post-cleanout rates increased as much as six-fold over precleanout rates as a result of these operations (73 to 411 Mscf/D for one well). Pre- and post-cleanout well test analyses performed on three wells indicated the cleanout operations resulted in increases in completion efficiency (more negative skin factors), permeability-thickness products, or both for each well. Analysis of four years of post-cleanout production data has shown the initial post-cleanout flow rates have been sustained, and it appears the cleanout operations have increased the ultimate recoveries for these wells.
Based on these initial results, CNR performed a pilot cleanout project in 1989 on four wells using a rotary rig for the cleanout operations. Many problems encountered using the cable tool rigs were avoided with the new procedure. Initial results have been encouraging.
Our analysis indicates a cleanout operation, on average, could increase estimated recovery by 210 MMscf over a 20-yr period. Assuming typical operating economic data, this increase in recovery could translate to a net present value of $197,000 per well. If 10% of the over 15,000 Devonian Shale wells in the basin were candidates for cleanout, this workover operation could translate to an increase in reserves of 315 Bscf with an associated net present value of $296 million.