Geochemical Analysis And Evaluation Of Exploration Wells In The Beetaloo Sub-Basin, Onshore Australia: Application Of Real-Time Elemental Measurement On Cuttings With Source Rock Mapping And Lateral Geosteering Implications
The scope of this paper is to illustrate the successful application of the Advanced Cuttings Characterization (ACC) service at the Amungee NW-1 and Amungee NW-1H wells drilled onshore in the Northern Territory, Australia. The prospective organically-enriched mudstones of the Mesoproterozoic-aged Velkerri Formation Amungee Member and Kyalla Formation, have TOC contents ranging from 4 to 8 %wt and 2 to 3%wt, respectively. The organic matter present within organically enriched intervals is oil-prone, but deep burial in the center of the Beetaloo Sub-Basin has resulted in the generation of commercially significant quantities of late maturity gas from the thermal cracking of retained oils and bitumen. In addition to thick organically-enriched intervals, the Velkerri Formation Amungee Member and Kyalla Formations also contain hundreds of meters of interbedded siltstones and mudstones with minor sandstone. An objective of the vertical exploration Amungee NW-1 well was to assess the Velkerri Formation Amungee Member as a potential regional shale gas play, by testing the lateral extent, facies variation, and physical reservoir properties of the organically-enriched mudstones. Origin Energy decided to use ACC, including Energy Dispersive X-ray fluorescence (ED-XRF) and high-resolution microscopy, to provide an accurate geochemical and mineralogical analysis while drilling Amungee NW-1 and Amungee NW-1H. The ACC service is a valuable formation evaluation tool. The ED-XRF is specially calibrated for sedimentary rocks, and measures major and trace elements. ED-XRF datasets are useful for: identifying element changes reflective of major and subtle lithology changes, quantifying bulk rock elemental composition of drilled formations, and identification of elemental changes as proxies for paleo-depositional environment conditions. High resolution digital photography of ditch cuttings assists in understanding, capturing and documenting observable facies changes, and is a valuable addition to the ED-XRF data. Specific goals for the employment of the ACC service were: to improve identification of lithofacies and paleo-environmental deposition indicators, to assist core point decision making, to assist vertical well termination decision making by the use of the specific XRF elemental ratios diagnostic of the Velkerri Formation Amungee to Kalala Member transition, and to assist in successful geosteering of the Amungee NW-1H lateral. During the drilling of both Amungee NW-1 and Amungee NW-1H, real-time Gamma Ray curves computed from quantitative measurement of potassium, thorium and uranium (ED-XRF) showed good correlation to wireline and Logging while Drilling (LWD) Gamma Ray. This correlation permitted robust quality control of the cutting lag depth, confirming cuttings provenance, and allowed the updating of formation prognosis depths using the computed Gamma Ray in real time. While drilling Amungee NW-1, ED-XRF revealed diagnostically high redox sensitive elemental proxies (Co, Mo, U, V) and productivity-sensitive elemental proxies (Cd, Cu, Ni, Zn) within the organically-enriched mudstones of the Velkerri Formation Amungee Member. These proxies indicated the organically-enriched mudstone intervals were likely deposited under strongly reducing conditions with high biogenic organic carbon input. The measured increased abundance of these diagnostic elements over the prospective organically-enriched mudstones of the Amungee Member in Amungee NW-1 (Vertical pilot), was used to assist geosteering of the Amungee NW-1H (Lateral sidetrack) into the highly prospective Amungee Member B Shale. Subsequent fracture stimulation and 57-day production testing recovering 66 mmscf gas at an average of 1.15 mmscf/day, with a final rate of 1.12 mmscf/day The combination of the ED-XRF and high resolution digital photography, included in the ACC service, proved to be a valuable, robust, low-risk and cost-effective formation evaluation tool in the Amungee NW-1 and Amungee NW-1H wells. The methodology developed in both wells provided real-time data measurement and interpretation, guiding the horizontal geosteering within Velkerri Formation Amungee. The data can be used for post-well analysis for greater geochemical understanding of penetrated geological formations.
AAPG Datapages/Search and Discovery Article #90331©2018 AAPG Asia Pacific Region GTW, Back to the Future – The Past and Future of Oil and Gas Production in the Asia Pacific Region, Bangkok, Thailand, September 26-27, 2018