Unconventional gas exploration in the Cooper Basin, Australia, has historically concentrated on fracture stimulation of tight gas sandstones within mapped structural closures. In drilling these sandstones, and other clastic reservoir targets, it has been recognised for many years that the Permian coal measures of the Toolachee, Epsilon and Patchawarra Formations record high levels of gas, often in excess of 4000 units, encountered at depths between 2500 and 3500m. Unlike shallower Coal-Seam-Gas reservoirs, which rely on de-pressuristion through de-watering to liberate adsorbed gas from the kerogen surface, deep coals are a "dry" system in which the free gas component is produced via kerogen and fracture permeability.
However maintaining a consistent and commercial flow rate from deep coals alone remained enigmatic until the first dedicated fracture stimulation program of deep Permian coals was commenced in the Moomba Field in 2007. Understandings of Permian source-rock reservoirs, the roles of the coal type and rank on sorption capacity and porosity, the influence of effective pressure and depth on coal permeability and the interrelation of coal fracture permeability with in-situ stress and mechanical stratigraphy has now advanced.
The deep Permian coal fairway in the Patchawarra and Nappamerri Trough of the Cooper Basin has been defined and mapped using a generative potential approach within a comprehensive 3D basin model. Net coal thicknesses from log electro-facies for 879 wells has been combined with available well maturity, TOC, HI and kerogen kinetic data, and calibrated against corrected temperatures in a basin-wide Trinity retention model which incorporates 14 mapped regional horizons. Play fairways have been overlain with observations of in-situ stress direction and fracture orientations from 3D seismic curvature volumes, FMI data and stress states from Mechanical Earth Models (MEM).
Within the basin, this approach has defined a P50 in-place resource of 14.6 TCF of gas and a P10 of 20.7 TCF of gas within the deep coals of the Permian Toolachee, Epsilon and Patchawarra Formations in Senex permits, of which 8-11 TCF is within the North Patchawarra Trough. MEM's have also demonstrated that deep coal seams are consistently in a normal stress state and therefore provide excellent scope for both propagating and constraining vertical fracture growth. Work is now underway to define further those areas, within the mapped resource parameters, which provide the best opportunity to site pilot lateral wells for multi-stage fracture stimulation within deep coals.
Ma, Chunguang (Research Institute of Exploration & Development, PetroChina Dagang Oilfield Company) | Zhao, Xianzheng (School of Resources and Environment, University of Electronic Science and Technology of China) | Zhao, Qing (Research Institute of Exploration & Development, PetroChina Dagang Oilfield Company)
Summary At present, multistage hydrofracturing technology aims to achieve full flow of oil and gas in the reservoir and is one of the key technologies for shale gas exploration and development. However, high uncertainty still exists in the currently available monitoring techniques for the depiction of fracturing zones. In this paper, we examine the plausibility of effectively monitoring the proppant distribution by borehole radar (BHR) surveys during the hydrofracturing stage increment through numerical simulation. The numerical simulation results demonstrate that it is possible to characterize the effective propped volume (EPV) of hydrofractured stages based on the permittivity and conductive changes in the shale gas field before and after fracturing. Introduction The multistage hydrofracturing technology aims to achieve full flow of oil and gas in the reservoir and is one of the key technologies for shale gas exploration and development.
We use least-squares migration to emphasize edge diffractions. The inverted forward modeling operator is the chain of three operators: Kirchoff modeling, azimuthal plane-wave destruction and path-summation integral filter. Azimuthal planewave destruction removes reflected energy without damaging edge diffraction signatures. Path-summation integral guides the inversion towards probable diffraction locations. We combine sparsity constraints and anisotropic smoothing in the form of shaping regularization to highlight edge diffractions. Anisotropic smoothing enforces continuity along edges. Sparsity constraints emphasize diffractions perpendicular to edges and has a denoising effect. Synthetic and field data examples illustrate the effectiveness of the proposed approach in denoisingand highlighting edge diffractions, such as channel edges and faults.
Presentation Date: Wednesday, October 17, 2018
Start Time: 8:30:00 AM
Location: 207A (Anaheim Convention Center)
Presentation Type: Oral
Estimation of scattering and intrinsic attenuation factors from seismic observations is of interest for subsurface imaging and characterization. We discuss a waveform inversion (WI) method for zero-offset seismic borehole data that explicitly models interference and multiple scattering in layered media using well logs. On the synthetic example, we show capability of WI to discriminate between scattering and intrinsic Q in 1D vertically inhomogeneous media. Depending on the scale of the supplied logs, the inverted Q-factors correspond either to the ‘effective’ attenuation or solely to the intrinsic absorption in rocks. We apply the WI to the nearly zero-offset VSP dataset acquired in the Nephrite-8 well (Cooper Basin, Australia). The borehole intersects the Patchawarra formation characterized by high-contrast interlayering of coal seams. For this formation, estimated intrinsic attenuation 1/Qint ≈ 0.014 is negligible compared to the stratigraphic filtering 1/Qscat ≈ 0.121±0.02. These 1/Qscat estimates are somewhat higher than those obtained by the application of the generalized O’Doherty - Anstey theory.
Presentation Date: Wednesday, October 17, 2018
Start Time: 8:30:00 AM
Location: 212A (Anaheim Convention Center)
Presentation Type: Oral
The complete paper proposes an azimuthal plane-wave-destruction (AzPWD) seismic-diffraction-imaging work flow to efficiently emphasize small-scale features associated with subsurface discontinuities such as faults, channel edges, and fracture swarms and to determine their orientation by properly accounting for edge-diffraction phenomena. The work flow is applied to characterize an unconventional tight-gas-sand reservoir in the Cooper Basin in Western Australia. Extracted orientations of edges provide valuable additional information, which can be used by the interpreter to locate finer-scale features and distinguish them from noise. Unconventional reservoirs may exhibit high structural variability, which is difficult to characterize with a discrete wells network. However, conventional images of the subsurface have low spatial resolution and are dominated by continuous and smooth reflections, which carry the information associated with only large-scale heterogeneities.
You have access to this full article to experience the outstanding content available to SPE members and JPT subscribers. To ensure continued access to JPT's content, please Sign In, JOIN SPE, or Subscribe to JPT The complete paper proposes an azimuthal plane-wave-destruction (AzPWD) seismic-diffraction-imaging work flow to efficiently emphasize small-scale features associated with subsurface discontinuities such as faults, channel edges, and fracture swarms and to determine their orientation by properly accounting for edge-diffraction phenomena. The work flow is applied to characterize an unconventional tight-gas-sand reservoir in the Cooper Basin in Western Australia. Extracted orientations of edges provide valuable additional information, which can be used by the interpreter to locate finer-scale features and distinguish them from noise. Unconventional reservoirs may exhibit high structural variability, which is difficult to characterize with a discrete wells network.
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 2695232, “Unconventional-Reservoir Characterization With Azimuthal Seismic Diffraction Imaging,” by Dmitrii Merzlikin, Sergey Fomel, Xinming Wu, and Mason Phillips, The University of Texas at Austin, prepared for the 2017 Unconventional Resources Technology Conference, Austin, Texas, USA, 24–26 July. The paper has not been peer reviewed.
Stratigraphic filtering (SF) or short-period multiples are prominent in cyclically stratified sedimentation with large impedance contrasts. Because SF attenuates and delays the propagating wavelet similar to the effects of Q attenuation, the integrity of well ties is often jeopardized. A method is proposed to obtain better well ties in areas with severe SF. Starting with a well-log acoustic impedance curve, two-way transmitted wavefields and their equivalent inverse filters are generated at each time sample. Since a time-varying convolution of the transmitted wavefields with the primary-only reflectivity yields the multiple reflectivity, a time-varying deconvolution of the multiple synthetic with the inverse filters yields the primary-only reflectivity. In essence, when the multiple synthetic matches the near-angle stack at a well location, the near-angle stack is deconvolved in a time-varying fashion to match the primary-only synthetic which then constitutes a correlation to the acoustic impedance yielding a good well tie. This new well-tie technique preserves the integrity of the lithologic interpretation since stretching and squeezing the time scale of the primary-only synthetic to force a seismic match is avoided. The proposed well-tie method is applied to both synthetic and field data from Cooper Basin, Australia where more than 30 coal beds are observed within a 1000-ft (304 m) interval.
Presentation Date: Wednesday, September 27, 2017
Start Time: 1:50 PM
Presentation Type: ORAL