Horizontal wells have become commonplace and have increased the effectiveness of coalbed methane or coal seam gas (CSG) reservoir drainage in Australia. To date, there have been limited applications of horizontal wellbores employing multiple hydraulic fractures, either because of potential wellbore instabilities during drilling, or regulatory restrictions on placing steel equipment within potentially mineable coal seams. Indirect hydraulic fracturing can allow operators to effectively deploy steel casing completions and apply multi-stage fracture stimulations along an indirect lateral underlying the targeted seam with lowered risk and impact to mining operations.
Detailed and calibrated modelling of an indirect hydraulic fracturing (IHF) application, based on observed pressure and diagnostic data, by Johnson et al., (2020) revealed the process is dependent on stress and rock mechanical properties of the coal and adjoining interval of fracture initiation. To illustrate the application and modelling steps for a difficult drilling case, history-matched reservoir modelling results from a Surat Basin case study are used to illustrate the application of and benefits derived by indirect fracturing. To illustrate the application for a mineable seam in the Bowen Basin, a 21-stage treatment in the Moranbah Goonyella Middle (GM) seam is presented and evaluated with recommendations for co-application with surface-to-inseam (SIS) wells.
Based on these calibrated case study data for both the Surat and Bowen Basin cases, guidelines for application of IHF (e.g., fracture space determination, injection rates, fluid parameters, proppant considerations, etc.) are outlined using results from planar 3D fracture modelling. Using reservoir simulation, the authors illustrate how IHF can improve the drainage effectiveness and improve projects by increasing the stimulated reservoir volume (SRV) relative to SIS wells. For existing fields with vertical or SIS wells, the go-forward benefit of indirect fracturing is reduced compartmentalisation through a larger SRV, greater interconnectivity between wells, and increasing overall recovery.
This work extends the learnings from the limited applications of IHF in an Australian CSG environment to broader applications in the Bowen and Surat Basins. The technology can be extended to other CSG areas where employing multiple hydraulic fractures from laterals have been limited, either because of wellbore instabilities or limitations of using steel equipment within a potentially mineable coal seam.