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This case study is about a landslide that occurred after 4 days of heavy rainfall, in the morning of June 29, 2012, in Cengong County, Guizhou Province of China, geographical coordinated 108°20′-109°03′E, 27°09′-27°32′N, with an estimated volume of 3.3×106 m3. To fully investigate the landslide process and formation mechanism, detailed geotechnical and geophysical investigations were performed including borehole drilling, sampling, and laboratory tests coupled with monitoring of displacement. Also, a combined seepage-slope stability modeling was performed to study the behavior of the landslide. After the heavy rainfall event, the sliding process started in this area. The landslide development can be divided into different parts. The man-made fill area, spatially distributed in the south side of the landslide area with low elevations, slid first along the interface between the slope debris and the strongly weathered bedrock roughly in the EW direction. Consequently, due to severe lateral shear disturbance, the slope in the main sliding zone slid next towards the SW direction, along the sliding surface developed within the strongly weathered calcareous shale formation located at a depth of 25-35 m. This means it was a rainfall triggered deep-seated landslide. Finally, retrogressive failure of a number of upstream blocks occurred, which moved in more than one direction. The initial failure of the man-made fill area was the 'engine' of the whole instability framework. This artificial material with low permeability, piled up in the accumulation area of surface and sub-surface and destroyed the drainage capacity of the groundwater. The numerical modeling results agreed with the analysis results obtained from the laboratory and field investigations. A conceptual model is given to illustrate the formation mechanism and development process of the landslide. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to investigate the effect of fracturing fluid/shale rock interaction on the rock physical and mechanical properties, the proppant embedment depth, and the fracture conductivity. The rich organic shale samples obtained from the Longmaxi (LMX) and Wufeng (WF) shale gas reservoirs, both located in Southern Sichuan Basin in China, were used for the experiments. The degree of proppant embedment upon rock/fluid interaction and resultant conductivity loss was directly measured in both types of rocks. Results show that the degree of alteration of the rock mechanical properties upon rock/fluid interaction depends on the mineral composition and the cementation of the shale matrix. The rock matrix cemented by clay minerals (e.g., LMX shale) was softer and more susceptible to alteration upon the rock/fluid interaction than that of the rock matrix cemented mostly by calcareous materials (e.g., WF shale). The conductivity tests carried out under 60 MPa closure stress have shown that the proppant embedment caused 47.55% reduction in the fracture conductivity of LMX shale samples with 34% clay content. While the fracture conductivity reduction due to proppant embedment was 25.94% in WF shale samples with 7% clay content. Based on the experimental results, it was concluded that upon rock/fluid interaction more significant reduction is expected in the rock physical and mechanical properties of the shale rocks with richer clay contents resulting greater proppant embedment depth and the higher fracture conductivity loss. [ABSTRACT FROM AUTHOR]

Abstract Shale oil refers to oil stored in organic-rich shale. It is an important part of unconventional oil and provides a large amount of resources. Based on the systematic study of the geological characteristics of shale oil in China's major continental basins, the geological connotation of the "sweet area (section)" in shale oil is proposed in this paper, and it refers to areas (sections) that can be preferentially explored and developed in oil-bearing shale formations under current economic and technical conditions. The formation conditions and distribution characteristics of continental shale oil in China are analyzed with a focus on the geological properties of the Triassic Yanchang Formation in the Ordos Basin, the Cretaceous Qingshankou Formation in the Songliao Basin and the Permian Lucaogou Formation of the Jimusar Sag in the Junggar Basin. It is found that the "sweet areas" of shale oil with medium-high maturation are mainly located in thick shales with a Ro greater than 0.9%, and the "sweet sections" are mainly located in the middle and lower parts of the shale formation. The geological resources of continental shale oil in the major continental basins in China are estimated to be approximately 3700 × 108 tons. The in situ conversion process (ICP) may be a key technology for the effective development of medium-to low-mature shale oil. The scale, maximum burial depth and present depth of the organic-rich shale are proposed as the three key parameters for the optimization of pilot sites by taking the Triassic Yanchang Formation in the Ordos Basin as an example. Using ICP, it is expected that the recoverable resources of China's continental shale oil will be approximately (400–500) × 108 tons. The terminology of "man-made reservoir" is proposed in this paper. In an "man-made reservoir", the overall industrial output of the "sweet areas (sections)" is formed by artificial intervention and the construction of an underground fracture network system with "man-made permeability". Continental shale oil may be another revolutionary source of unconventional oil and is expected to be first successfully produced in China. Highlights • The "sweet areas(sections)" of continental shale oil with medium-high maturation are illustrated with examples and the resources are assessed. • The formation conditions and distribution characteristics of continental shale oil in China are analyzed. • Some important concepts are proposed, including "exploring oil into source kitchen", "source rock oil", "man-made oil reservoir", etc. [ABSTRACT FROM AUTHOR]

The casing deformation problems during hydraulic fracturing process in shale gas wells seriously affect multi-stage hydraulic fracturing treatment and cause significant impact on efficient exploitation of shale gas in Sichuan, China. But by now, the mechanism of these casing deformation problems has not been completely understood. The tests of the casing deformation show that the shear failure is the main type of casing deformation. Combined with the detected seismic data, the fault slip caused by hydraulic fracturing is identified as the main reason for casing deformation in shale gas wells. A deep understanding of fault reactivation and slip is significant important. Hence, a semi-analytical model for calculating induced stress along the fault caused by hydraulic fracture is established in this paper. Based on the induced stress along the fault, semi-analytical models for calculating two types of fault slip are established, including the reactivated zone located at one fault tip and the reactivated zone located away from fault tips. Additionally, the effects of fluid pressure, dip angle of fault, scale of fluid stimulated area and the friction coefficient on fault slippage are discussed. At last, the method for calculating fault slippage proposed in this paper is applied in field and the calculated result is consistent with the field data. The semi-analytical model proposed in this paper provides a reasonable way for identifying casing deformation in shale gas wells or other wells which need hydraulic fracturing treatments. [ABSTRACT FROM AUTHOR]