Hydraulic fracturing has been widely used to develop coal seam gas (CSG) resources worldwide and improve gas production from CSG wells. An optimal stimulation in CSG, in particular with lower permeability coals lacking a well-developed cleat system, creates a fracture with sufficient length and orientation along the maximum horizontal stress (σHmax) direction such that the fracture intersects the existing hydraulically-conductive natural fracture network in an a way that maximizes the stimulation effect. In the Walloon Coal Measures (WCM) in the Surat Basin in eastern Australia, induced fractures have been observed to grow in a way which does not optimally intersect the natural fracture network or conform to the σHmax azimuth. This resultant stimulation of the natural fractures, as opposed to the construction of a conductive path crosscutting the natural fracture system and linking it to the wellbore, has proven to reduce the effect of stimulation in vertical wells.
This paper will present a two-well program in the WCM where the wells have been directionally drilled along the σHmax direction with different deviation angles from vertical. Both wells have been stimulated with a combination of treated water with a low proppant concentration, followed by crosslinked-gelled water with a higher proppant concentration. There are two microseismic observation wells and twenty one tiltmeters to map the fracture propagation and determine the fracture geometry.
The diagnostic results from microseismic wells and surface tiltmeters for each hydraulic fracturing stage will be outlined in this paper. These results, compared with similar diagnostic results from nearby offset vertical wells, are encouraging and indicate consistent fracture growth along the maximum horizontal direction for all stages. These results indicate that hydraulic fracture geometry can be improved by directional drilling.