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The pore‐throat structure and fluid mobility are the key factors of tight sandstone reservoir classification and evaluation. Taking the Jurassic Shaximiao Formation tight sandstone reservoir in Central Sichuan Basin as an example, 19 samples were analysed by casting thin sections, scanning electron microscopy, high‐pressure mercury injection and nuclear magnetic resonance to clarify the pore‐throat structure, the fluid motility and its controlling factors. The results show that the pore type of Shaximiao Formation tight sandstone reservoir consist of intergranular pores, dissolved pores and a few microfractures. Based on the feature of capillary pressure curve, the pore‐throat structure was classified into three types, corresponding to different movable fluid characteristics. The Type I has large pore and throat radius, good pore‐throat connectivity, small fractal dimension, weak reservoir heterogeneity and strong fluid motility. The distribution range of pore‐throat radius is mainly from 0.3 to 1.1 μm and the average movable fluid porosity (MFP) and movable fluid saturation (MFS) are 6.04% and 49.93%. The Type II has poor pore‐throat sorting, weak fluid motility and the distribution range of pore‐throat radius is 0.01–0.03 μm and 0.2–0.8 μm. The average MFP and MFS of Type II are 1.13% and 14.3%. The Type III has the smallest pore‐throat radius and the largest fractal dimension, corresponding to the most complex pore‐throat structure, which lead to the worst fluid mobility. The average MFP and MFS are 0.49% and 12.76%. The fluid mobility of the tight sandstone reservoir is affected by physical properties and pore‐throat structure. The reservoirs with large pore‐throat size, good connectivity between pore and throat, and low heterogeneity have higher MFP and saturation. Moreover, the mineral compositions have different effects on fluid mobility of the tight sandstone. The feldspar positively affects fluid mobility, while the clay minerals negatively affect fluid mobility. [ABSTRACT FROM AUTHOR]

The Ediacaran Dengying Formation fourth member in Central Sichuan Basin is the deep dolomite gas reservoir with the largest natural gas reserves in China, providing an excellent example for understanding the effect of hydrothermal silicification on deep dolomite reservoir quality. By integrating petrology, geochemistry and physical property measurement, this study aims to reveal the genesis of different quartz phase and their corresponding diagenetic events, and to discuss the temporal relationship of diagenetic events and their effects on the quality of deep dolomite reservoir in Dengying fourth member. Three phases of quartz cement are identified in Ediacaran Dengying Formation deep dolomite reservoirs of Central Sichuan Basin as follows: (1) first‐stage quartz filled in primary reservoir spaces, (2) second‐stage quartz mainly filled in secondary reservoir spaces, and (3) third‐stage quartz filled in secondary reservoir spaces with Mississippi Valley‐Type minerals. By analysing petrographic and temporal relationships between these fabrics, it is suggested that the first‐stage quartz precipitated during the syndiagenetic stage, the second‐stage quartz precipitated during middle diagenetic stage, and the third‐stage quartz precipitated during middle diagenetic stage as well. Silicification during syndiagenetic stage is characterized by replacement of cryptocrystalline quartz and cementation of first‐stage quartz within matrix dolomite (MD). After syndiagenetic silicification, the mineral composition of the MD changed from magnesium calcium carbonate to silica, and the later constructive diagenetic alterations were almost ineffective. The distribution of syndiagenetic silicification during syndiagenetic stage gradually decreases from the platform‐interior to the platform‐margin. The second‐stage and third‐stage quartz cements, derived from two‐stage hydrothermal silicification in the middle stage, are both destructive for reservoir preservation. This study, combined with coeval vapour–liquid inclusions Th data and thermal‐burial models, constrains the time of the second‐stage quartz to ca. 403–408 Ma, suggesting an hydrothermal silicification related to the Caledonian movement. The time of the third‐stage quartz cement is constrained to ca. 259.4 Ma, associated with Late Permian eruption of Emeishan flood basalts. [ABSTRACT FROM AUTHOR]

This article concentrates upon the adaptive secure containment control problem for a class of uncertain nonlinear multi‐agent systems with the output constraint requirements under denial‐of‐service (DoS) attacks. At first, to overcome the difficulty that the tracking performance of the nonlinear multi‐agent systems under the DoS attacks is disturbed seriously, a novel adaptive secure containment control approach is presented by applying a DoS attacks detection mechanism and introducing the barrier Lyapunov functions, which enables the system to achieve the security control objective that the output of each agent eventually converges to the convex hull spanned by the dynamic leaders' outputs, while never violating the output constraints. Then, a state estimator is designed, which reconstructs the immeasurable states of the multi‐agent systems and approximates the completely unknown nonlinearities arising from the agents. In addition, the dynamic surface control technique is used to solve the "explosion of complexity" problem. It is demonstrated that the proposed anti‐attack controller ensures that all the signals of the closed‐loop system are semi‐globally uniformly ultimately bounded. Finally, a simulation example is provided to illustrate the effectiveness of the theoretical results. [ABSTRACT FROM AUTHOR]

Based on comprehensive analyses of occurrence, petrological observation, pore structure and geochemistry, the different reservoir characteristics and reservoir evolutionary pathways between different oolitic shoal reservoir types of the Feixianguan Formation on the west side of the Kaijiang‐Liangping Trough have been studied. There exist three stages of high‐energy slope break belts in the Feixianguan period, the corresponding three stages of oolitic shoals gradually migrating in the direction of the trough. Three types of oolitic shoal reservoirs, namely, residual‐oolitic dolomite, mold‐oolitic dolomite and sparry oolitic limestone, were formed during sedimentary‐diagenetic evolution, the pore types being intergranular dissolved pore, mold pore (or intragranular dissolved pore) and residual intergranular pore, respectively. The petrology, physical properties and pore structure of the different types of oolitic shoal reservoirs are quite different. Residual‐oolitic dolomite reservoirs have the best quality, while sparry oolitic limestone reservoirs have the poorest. Combined with analyses of trace elements, rare earth elements and carbon‐oxygen isotopes, it is suggested that the formation of residual‐oolitic dolomite reservoirs is jointly controlled by penesaline seawater seepage‐reflux dolomitization and hydrothermal dolomitization. Mold‐pore oolitic dolomite reservoirs are controlled by penesaline seawater seepage‐reflux dolomitization and meteoric water solution. The burial dissolution of organic acid not only further improves the reservoir qualities of previously formed oolitic dolomite reservoirs, but also preserves residual intergranular pores in the sparry oolitic limestone reservoirs. [ABSTRACT FROM AUTHOR]

Hydrothermal mineral assemblages and related hydrothermally enhanced fracturing are common in the Precambrian Dengying Formation of Central Sichuan Basin. Petrographic and geochemical analyses of core samples show that the hydrothermal dolomite reservoirs of Dengying Formation consist of four main types of pores in the reservoir facies. These include: 1) hydrothermal dissolution vug (or pore), 2) intercrystalline pore, 3) residual inter‐breccia vug (or pore), and 4) enlarged dissolved‐fracture. There are three different fabrics dolomite in hydrothermal dolomite reservoirs, namely, saddle dolomite, fine‐medium dolomite and micritic dolomite. Micritic dolomite is the original lithology of host rock. Saddle dolomite with curved or irregular crystal faces was directly crystallized from hydrothermal fluids (average temperature 192°C). Fine‐medium dolomites are the products of recrystallization of micritic dolomite, resulting in abnormal geochemical characteristics, such as slight depletion of δ18O, significant enrichment of Mn‐Fe and 87Sr/86Sr, and positive Eu anomaly. A model for the distribution of various hydrothermal dolomite reservoir facies is proposed here, which incorporates three fundamental geological controls: 1) extensional tectonics and tectono‐hydrothermal events (i.e., the Xingkai Taphrogenesis of Late Sinian‐Early Cambrian, and Emei Taphrogenesis of Late Permian), 2) hydrothermal fluid storage in clastic rocks with large thickness (e.g., Nanhua System of Chengjiang Formation and part of Doushantuo Formation), and 3) confining bed for hydrothermal fluids (such as, the shale in Qiongzhusi Formation). The supply of hydrothermal fluid is critical. Large basement‐rooted faults and associated grid‐like fracture system may function as the channels for upward migration of hydrothermal fluid flow. The intersection of the above‐mentioned faults (including the conversion fault), especially transtensional sags above negative flower structures on wrench faults can serve as a key target for future hydrocarbon exploration. [ABSTRACT FROM AUTHOR]

On the basis of the core description, thin sections, and geochemistry data, we characterized the Lower Silurian Longmaxi marine shale in the Changning area in the south Sichuan Basin. Ten lithofacies were identified in the Lower Silurian Longmaxi marine shale: (a) massive silty shale (Lithofacies A); (b) laminated siliceous calcareous shale (Lithofacies B); (c) calcareous shale (Lithofacies C); (d) silty dolomitic shale (Lithofacies D); (e) argillaceous siltstone (Lithofacies E); (f) siltstone (Lithofacies F); (g) laminated silty shale (Lithofacies G); (h) silty calcareous shale (Lithofacies H); (i) argillaceous lime shale (marl) (Lithofacies I); and (j) bentonite (Lithofacies J). Obvious heterogeneity occurred in different lithofacies in terms of mineralogy, total organic carbon (TOC) content, porosity, permeability, pore surface area, total pore volume, and total gas content. Among these lithofacies, Lithofacies B has the highest porosity (5.4%), pore surface area (12.79 m2/g), total pore volume (0.015 cc/g), TOC content (4.37%), total gas content (3.4 m3/ton), and relatively high brittle minerals, suggesting great shale gas potential. Lithofacies A, C, and D have a relatively high brittle minerals, porosity, pore surface area, total pore volume, TOC content, and total gas content, which means that these 3 lithofacies show relatively good potential for shale gas. The rest of the lithofacies have low brittle minerals content, porosity, pore surface area, total pore volume, TOC content, and total gas content, representing poor shale gas potential. [ABSTRACT FROM AUTHOR]