The Coal Seam Gas (CSG) industry is currently focused on the large-scale development of a number of Liquefied Natural Gas (LNG) projects in Queensland, Australia. Arrow Energy is one of four proponents undertaking to develop such a project, with a focus on the Surat and Bowen basins. Arrow Energy also supplies gas to power stations, mineral refining facilities and ammonium nitrate plants in north Queensland. They are committed to maintaining the supply to these domestic customers and to the growing international gas market through the LNG project at Gladstone, Australia through its CSG projects.
The wells discussed in this paper are situated within Arrow Energy's tenements in the northern Bowen Basin. The targeted coal measures in the region usually occur at depths between 230m to 500m below the surface. A number of wells have been drilled in these coal measures and completed either by open-hole, horizontal drilling or, less frequently, hydraulic fracturing. To maximize the productivity, and thus success of these projects, there is a distinct need to understand the wellbore stability of horizontal wells as well as the potential for hydraulic fracture containment in the target formations.
Rigorous one-dimensional Mechanical Earth Models (1D MEMs) were constructed utilizing:
A complete suite of wireline logs, processed and interpreted for the purpose of construction of the models;
Rock mechanics laboratory tests;
Closure pressures obtained from Diagnostic Fracture Injection Tests (DFIT);
Drilling-induced borehole failures when drilling the wells.
The 1D MEMs were constructed for utilizing data acquired specifically for the construction of the models. The models reveal the variation of maximum horizontal stress direction, coal properties in the various layers and contrast in stresses between the coal seams and inter-burden formations.
This paper presents the workflow used in the construction of the 1D MEMs for the CSG project applications, and the results obtained. The particular focus is on the following:
Data acquisition strategy (logs that were acquired for the construction of the 1D MEMs).
Rock mechanics laboratory tests performed, the results obtained, and how these results were utilized in calibrating the 1D MEMs.
Closure pressure estimates derived from well tests (DFITs), and how these results were utilized in calibrating the minimum horizontal stress.
Borehole image log interpretation and characterization drilling-induced features (break out and drilling-induced fractures) that yield the direction of maximum horizontal stress and for calibrating the wellbore stability models.
Predominant strike of fractures in the coal from advanced sonic tool.