A coal seam gas (CSG) to liquefied natural gas (LNG) project in Queensland, Australia, has an active exploration and appraisal program in support of future development activities. Critical to exploration and appraisal is the evaluation of permeability, skin, and reservoir pressure. Drill stem testing (DST) has been the most common form of evaluation since the inception of the industry in Queensland over the last 10 years. DSTs commonly used in the CSG industry are modified ‘slug’ tests in which a water cushion provides hydrostatic backpressure on the formation to reduce the likelihood of gas break-out and two-phase flow. Although DSTs have become an industry-accepted method for evaluating permeability, skin, and extrapolated reservoir pressure, there are some disadvantages to this approach.
A new wireline formation testing technique addresses the evaluation objectives of CSG testing in the Surat and Bowen basins. In addition to efficiency and cost-effectiveness, the approach provides additional testing flexibility; this includes the ability to manage a broad range of drawdown and inflow rates, extending its applications from very low to high permeability coals. Additional applications include step-rate tests, across both the Walloon coal measures of the Surat basin and the Bowen basin's Bandanna formation.