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As the demand for ore resources increases, the target for mineral exploration gradually shifts from shallow to deep parts of the Earth (>1 km). However, for the ore-hosting strata, it is difficult to obtain high-resolution images by using the electromagnetic method. Seismic full waveform inversion (FWI) is an optimization algorithm which aims at minimizing the prestack seismic data residual between synthetic and observed data. In this case, FWI provides an effective way to achieve high-resolution imaging of subsurface structures. However, acquired seismic data usually lack low frequencies, resulting in severe cycle skipping of FWI, when the initial velocity model is far away from the true one. Phase information in the seismic data provides the kinematic characteristics of waves and has a quasi-linearly relationship with subsurface structures. In this article, we propose to use a phase-amplitude-based full waveform inversion with total-variation regularization (TV-PAFWI) to invert the deep-seated ores. The ore-hosting velocity model test results demonstrate that the TV-PAFWI is suitable for high-resolution velocity model building, especially for deep-seated ores.

The width of reservoir-scale fault damage zone governs fluid flow of the tight reservoirs in subsurface petroliferous basins. Together with cores, thin sections, geophysical well logs, and production data from more than 60 wells, we describe fracture attributes and fault damage zones associated with a conjugate strike-slip fault system in tight Ordovician carbonate rock at depths of between 6500 m and 7500 m in the Tarim intracratonic basin in NW China. Fracture frequency, aperture, and oil production in wells reveals a power-law relationship with the distance from fault cores, with a variation in two orders of magnitude. The cumulative data of fracture frequency, aperture and oil production show multiple gradients in slope with the distance. Except for sampling bias, the varied gradients are possibly related to the overlaying multiple fault zones or multiple sections along a large fault zone, which are useful to constrain damage zone width. Together with fracture frequency, cumulative fracture frequency, aperture and oil production, four major damage zone boundaries are identified at ∼200, ∼420 m, ∼780 m and ∼1100 m. Therefore, a wide fault damage zone with a width of more than 2 km in the carbonate rocks could be inferred, which mostly depends on the interaction and superposition of secondary faults. In addition, there is a relatively high fracture frequency decay exponent (>1) with distance, which is possibly related to fault size, fault splays, background fracture frequency and the lithology. In turn, the growth of wide damage zone also resulted in a large scattered distribution of the fracture attributes with the distance from fault cores. Attributes of fractures of various scales from the deep subsurface provide powerful tools for assessing damage zone width and growth.

With the gradual disappearance of traditional structural reservoirs, widely distributed deep thin lithologic reservoirs developed in continental and transitional sedimentary environments may offer significant petroleum reserves. Reservoir characterization through conventional impedance inversion methods without appropriate selection of regularization parameters and other empirical constraints cannot easily detect and assess these reserves, however, due to their size, variation, and features that conceal them. We have evaluated a nonlinear chaos inversion method that uses well data and seismic facies to characterize the oil and gas reservoirs of the Tazhong oil field in the Tarim Basin, China. The inverted results exhibited high agreement with the well data in highlighting the interfaces and lithologic bodies. This integrated method also provided enhanced resolution of depositional contacts and variable lithologic bodies. Specifically, the approach was able to describe a highly variable, approximately 5 m thick Carboniferous formation at depths greater than 3400 m. Borehole and core data provided a complementary hydrocarbon accumulation model. We used background information on hydrocarbon-bearing units within the main structure (an anticline) to detect and access (drill) ultra-thin lithologic reservoirs located in deeper areas of the structural high. Two wells drilled according to predictions derived from this new approach have each reached production rates of more than 30 tons of oil per day. Thus, we have determined the effectiveness of combining chaos inversion methods with empirical constraints in exploration of deep thin hydrocarbon reservoirs.

Architecture and permeability of fault damage zones are important for understanding faulting mechanisms and fluid flow in fractured rocks. Nevertheless, this understanding is often hindered by limited availability of data, especially in the subsurface. A comprehensive suite of cores, logs and production data is here presented to unravel petrophysical properties and fracture characteristics of deep (>6000 m) Ordovician limestones within strike-slip fault zones of the Tarim intracratonic basin (NW China). The results show that (1) the carbonate porosity is mainly secondary dissolution porosity and comprises low porosity ( 5 mD) and high porosity (>8%); (2) fault damage zones are generally tight with fracture aperture