Pioneering Beetaloo Shale Appraisal: Case Study of Australia's Largest Multistage Fracturing Operation

Abstract

Abstract In the Beetaloo Sub-basin within the Northern Territory, Australia, the shales of the Velkerri and Kyalla Formation are highly prospective. The Carpentaria-3H well was drilled in the B Shale of the Amungee Member of the Velkerri Formation with a lateral length of more than 2,632 metres and completed over a 1,989-metre section. Beyond the appraisal nature of work, the observation of natural fractures and faulting coupled with geomechanical complexity posed multiple challenges to the planning, design, execution, and evaluation of Australia's largest stimulation job to date. This paper provides a comprehensive review of the Carpentaria-3H fracturing design and operation, following incorporating data from the Carpentaria-2H well. Completion design included developing the fracture stage interval spacing, number of clusters per stage, and cluster perforation density. For the fracturing treatment, decisions were refined for selection of fluid and proppant type, job volume optimisation and differentiation. Design optimisation is based upon both the simulator and evaluation measurements from the Carpentaria-2H reference well. Furthermore, observations from field execution, including formation response, experimental fracturing stages, and onsite design optimization, were incorporated. The largest multi-stage fracturing operation to date in Australia was completed with 12.8 million pounds of sand and proppant successfully placed without screen out across 40 stages. Across the multiple stages trials of sleeve-perforation comparison, out-of-target stages, variable sand size and ceramic proppant were successfully executed. During post-fracturing cleanup, the Carpentaria-3H produced at an average rate of 2.6 MMscf/D over 27 days prior to being shut-in for a period of "soaking". The success of the well completion through a multi-stage fracturing operation marked a breakthrough in Beetaloo Sub-basin appraisal and demonstrated that long lateral drilling and large-scale fracturing treatments can be a viable pathway to improve efficiency and return on investment. This is despite the limitations imposed by scarce infrastructure and challenging logistics in the Australian outback. Knowledge from the evaluation work undertaken in the previously stimulated and tested Carpentaria-2H wells was critical to advancing the Carpentaria-3H project. The Carpentaria-2H well's multi-arm calliper measurements offered enough precision to evaluate the perforation erosion following proppant placement. This generated a new technique for indirect evaluation of fluid and proppant distribution among the clusters. Production logging and chemical tracers also provided useful information for calibration and design optimization. Furthermore, advanced software tools were applied to integrate reservoir modelling, fracture and reservoir simulation, and data analysis.