Producing gas from low permeability coals
An assessment framework for selecting optimal drilling and completion, forecasting and operating procedures in low permeability coals. Themes covered: low permeability coal drilling and production alternatives; production forecasting and operating procedures; and, economics and technical feasibilty. Arrow Energy Limited has been exploring for and producing from moderate to low permeability coals for over eight years, both in Australia and internationally. Arrow has developed a systematic approach to assessing the optimal drilling and completion, forecasting and operating procedures to evaluate the best appraisal and development options. Following the confirmation that the coal resource is of low permeability (less than 5mD) the selection of the drilling and completion strategies is inter-linked with the expected production and operating procedures. This paper summarises the approach taken by each of these discipline areas and maps out the key alternatives, data requirements and selection criteria used to recommend a production pilot in a low permeability environment. The first stage of the assessment is to review the drilling alternatives. This includes consideration of horizontal versus deviated or vertical wells, wellbore stability and solids production conditions, stimulation requirements and the production string, including artificial lift. Production forecasting is conducted with due regard to the technical alternatives screened as part of the drilling assessment. The quality of the forecast will be determined by the available data and the use of the appropriate forecasting tools ranging from analogue assessments, simple single well modelling through to 3D reservoir modelling. Finally, the production procedures appropriate for the well will be selected based on the well configuration and forecast deliverability as well as regional geology and geomechanics. This framework ensures that a consistent methodology is applied for selecting well type and operations that maximises the flow potential from our low permeability coals while ensuring due consideration to economics and technical feasibility.