The Open Petroleum Engineering Journal
2017, 10 : 108-117Published online 2017 April 28. DOI: 10.2174/1874834101710010108
Publisher ID: TOPEJ-10-108
RESEARCH ARTICLE
Study of Cyclic Fracturing in Vertical CBM Wells
* Address correspondence to this author at the Mechanical Engineering College of Yangtze University, School of Mechanical Engineering, 1 Nanhuan Rd, 434023 Jingzhou City, Hubei Province, P. R. China; Tel/Fax: +8613797507143; E-mails: , wanjifang@126.com
ABSTRACT
Background:
Coal-bed methane productivity of single well is very low, and has been the bottleneck of the coal-bed methane industry in China.
Objective:
Although hydraulic fracturing is the only stimulation measure to develop CBM, it cannot increase production effectively, conventional fracturing method to create opening fractures should be improved. How to make good use of natural fractures, which are plentiful in CBM reservoirs, is also an important subject for hydraulic fracturing.
Method:
In this paper, the plastic deformation of coal rock is analyzed by harnessing a pseudo-Maxwell creep phenomenon, which is normally present in rock. The Kelvin-Voigt model is utilized to describe pseudo-plastic behavior of coal rock to determine pressurization and decay cyclic time for cyclic fracturing design. The mechanical requirement for shearing natural fractures is also analyzed, and shearing distance between the faces of natural fracture can be calculated by Westergaard stress function. Ultimately, the cyclic fracturing method is proposed according to theories about stress alteration and shearing of natural fractures. This method includes such periods as fracturing, pumping shut-down and so on.
Conclusion:
A complex fracture system can be created, which consists of opened and sheared fractures, then, large SRV(stimulated reservoir volume)and flowing drainage area can be acquired. In comparison with conventional fracturing method, this new way can make full use of the characteristics of CBM reservoirs and is more suitable to CBM. This method will lead to a significant increase of CBM production, and will achieve huge economic benefits.