The Benefits of Reworking Declining CBM Wells

摘要

There are three distinguishing phases in the production life of a wet CBM well: a period of inclining gas rate due todominance of relative permeability effects, a period of rate stabilization during which the gas rate peaks followed by thedepletion phase during which gas production rate declines. The declining gas production rate can be attributed to many factors such as:1. Declining reservoir pressure2. Loss of productivity due to compaction and permeability loss3. Loss of productivity due to fine migration that creates a choke skin near wellbore While the decline in reservoir pressure is inevitable, the loss of productivity due to the choke skin and permeability lossfor a declining CBM well can be remedied or slowed down through a multi-stage hydraulic refracturing. The impact of suchfracturing on improving well productivity and boosting the gas production rate is investigated. Reworking the well through refracturing could help clean up the zone near wellbore, re-activate or improve the coalnetwork of natural fractures; lead to more effective dewatering and even create new contacts between the reservoir andformation. The area near wellbore will benefit from re-invigoration of fracture network and creation of an area of enhancedpermeability. In this study the benefit of completing a new vertical and/or horizontal CBM well with a multi-stage hydraulic fracture isexamined. The production of wells with such completions are compared to typical single-stage fracturing and benefits ofcreating an inner zone of enhanced permeability in short-term and long term are investigated. A numerical dual-porosity reservoir model is used to generate the CBM gas production forecasts.