Page 269 - Fundamentals of Enhanced Oil and Gas Recovery

Enhanced Gas Recovery Techniques From Coalbed Methane Reservoirs 257

Figure 8.7 Schematic view of microsized graded proppant injection into the natural cleat network
connected to the main hydraulic fracture. After Keshavarz, A., Johnson, R., Carageorgos, T.,
Bedrikovetsky, P., Badalyan, A., 2016. Improving the conductivity of natural fracture systems in conjunc-
tion with hydraulic fracturing in stress sensitive reservoirs. In: SPE Asia Pacific Oil & Gas Conference and
Exhibition. Society of Petroleum Engineers.

Keshavarz et al. coupled the graded proppant injection technique with hydraulic
fracturing treatment in CBM reservoirs to enhance postfrac conductivity of cleat net-
work around the created hydraulic fracture [76,77]. In this method, microsized mono-
layer proppant particles are leaked-off into the natural cleat system at the leak-off
pressure condition, as seen on Fig. 8.7 [96]. The proppants placed inside the cleat net-
work maintain the cleat network conductivity and uphold the connectivity between
natural cleat system and the main hydraulic fracture during the post fracturing produc-
tion. Application of this technique can significantly improve the efficiency of hydrau-
lic fracturing in CBM reservoirs by expanding the stimulated reservoir volume. In
addition, the graded microsized proppants placed inside the cleat network decrease
the fluid loss due to leak-off during the hydraulic fracturing operation, which cause
the extension of the fracture half-length.

8.5.2 Enhanced Coalbed Methane Recovery

ECBM recovery is a secondary production mechanism to enhance the methane ulti-
mate recovery and/or improve methane production rate, by means of injecting a for-
eign gas. The commonly used gases are nitrogen (N 2 ), carbon dioxide (CO 2 ), or a
mixture of N 2 and CO 2 . If the injected gas contains CO 2 , the ECBM can be also
beneficial from a carbon sequestration standpoint.