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Wang R.,China University of Geosciences | Gu Y.,China University of Geosciences | Ding W.,China University of Geosciences | Gong D.,China Energy Reserve Corporation | And 7 more authors.
Journal of Natural Gas Science and Engineering | Year: 2016

The Lower Cambrian organic-rich marine shale, which is a significant source of China's shale gas, is widely distributed in southern China. An integrated characterization of the Niutitang shale is provided in this study in terms of organic geochemistry, mineralogy, pore characterization, methane sorption capacity, rock mechanical properties, fractures and gas content based on samples from three wells. The results indicate that the Lower Cambrian Niutitang shale is thermally over-mature and has rich shale gas resources, with a total organic carbon content (TOC) between 0.51% and 10.49% and a high quartz content between 35.3% and 78.5%. Compared to the major gas-producing shales in the U.S. and China, most of the organic matter (OM)-hosted pores in the Niutitang shale are generally smaller than 5 nm, significantly affecting the methane sorption capacity. The inter-particle and intra-particle pores and fractures are the primary sources of storage space, especially for free gas. For samples with TOC values less than 6.5%, TOC is positively correlated with the total porosity, total pore volume, brittleness (Young's modulus), core fracture density, free gas content and Langmuir pressure; however, for samples with TOC values greater than 6.5%, the positive correlations become negative. These characteristics are due to the ductility and low hydrocarbon generation potential of organic matter in high thermal maturity shales that are vulnerable to compaction. Thus, TOC has a significant impact on the macroscopic (e.g., brittleness) and microscopic (e.g., pore structure and sorption capacity) properties of shale reservoirs, potentially controlling the enrichment and productivity of shale gas. These results can be used to optimize drilling and fracturing stimulation intervals during shale gas exploration and development. © 2016 Elsevier B.V.


Leng J.-G.,China Energy Reserve Corporation | Leng J.-G.,Tongren Sino Energy Natural Gas Corporation | Leng J.-G.,Beijing Sino Shale Gas Engineering Corporation | Han J.-H.,Chengdu University of Technology | And 3 more authors.
Natural Gas Geoscience | Year: 2014

The shale gas resources are rich in Upper Yangtze platform, especially in the Niutitang Formation. Huayuan shale gas block is located within the shale gas abundant play of Niutitang Formation in Upper Yangtze platform. Based on the stratigraphic correlation, reservoir analysis and geochemical analysis of source rock samples and in combination with previous study results, the structure, source rock and reservoirs characteristics of the Niutitang Formation in Huayuan block was systematically studied. The distribution range of the Niutitang Formation, reservoir physical property and thickness of source rocks were mapped. Furthermore, the resource volume of shale gas was calculated by using the gas content data obtained from testing in well Yuke 1 and well Cenye 1. The kerogen types of the Niutitang Formation in the Huayuan shale gas block wereIand II1. With average values of TOC and RO of 3.52% and 3.58%, respectively, reflecting the source rock has entered intoover-maturity stage. The reservoirs characteristics are low porosity-ultralow permeability and high specific surface area. The recoverable resource volume of shale gas is estimated up to 3.18 billion cubic meters. The area from Minle to Longzhai, in the middle-upper of the Huayuan block can be selected for the further exploration and evaluation.


Wang R.-Y.,China University of Geosciences | Ding W.-L.,China University of Geosciences | Gong D.-J.,China Energy Reserve Corporation | Gong D.-J.,Tongren Sino Energy Natural Gas Corporation | And 4 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2015

Shale gas resources are abundant in China. Recently, China has achieved a breakthrough on the Lower Silurian Longmaxi shale in Sichuan basin and its surrounding areas. Compared with the Longmaxi shale, the Lower Cambrian Niutitang shale, which has a greater deposition thickness and wider distribution area, is a significant strata for China's shale gas. The feature of “source-storage integration” makes the evaluation of the total organic carbon (TOC) content as a significant research content in shale gas exploration and development. In this paper, the Δlg R, natural gamma ray spectrometry, density and multiple linear regression logging methods were used to calculate the TOC content of the Niutitang shale in the Cengong block on the basis of logging response and the geological features of overmatured marine organic-rich shale in the complex structural area in southern China. The calculation accuracy and applicability of each method were compared and analyzed. As a result, the calculation accuracies of the Δlg R, natural gamma ray spectrometry, density and multiple linear regression logging methods increase successively. The Δlg R method is not applicable for overmatured marine shales, which locate in the complex structural areas and have large differences of preservation. The natural gamma ray spectrometry and density logging methods have relatively high accuracy and applicability. Furthermore, the multiple linear regression logging method, which uses logging parameters that correlated with TOC content, can further improve the accuracy and applicability. Besides, some logging parameters such as resistivity and acoustic travel time (AC) are sensitive to gas content, fluid properties and preservation, which can be used as the indicators of shale gas content and preservation. © 2015, China Coal Society. All right reserved.


Wang R.,China University of Geosciences | Ding W.,China University of Geosciences | Gong D.,China Energy Reserve Corporation | Gong D.,Tongren Sino Energy Natural Gas Corporation | And 5 more authors.
Oil and Gas Geology | Year: 2016

South China, where develops several sets of marine organic-rich shales, is an important area for shale gas E & D. Compared with North America, the marine organic-rich shales in southern China have the characteristics of old geologic age, high maturity, multi-episodic tectonic movements, complex surface conditions, complicated earth stress state and large differences of preservation conditions. In comparison with the Longmaxi shale that has achieved a breakthrough in shale gas exploration and development in Sichuan Basin and its periphery, the Lower Cambrian Niutitang shale has an older age, greater particularity and complexity and higher requirement to preservation conditions. On the basis of the geological conditions of the complex structure areas in southern China, the preservation conditions of the Niutitang shale in the Cen'gong block were analyzed through precise seismic interpretation, tectonic evolution, material foundation, cap rocks, reservoir pressure, and component of natural gas and aquifers. The results indicate that late tectonic reconstruction dominated by denudation and faulting is the major factor leading to the dissipation of shale gas. The tectonic evolution of the study area has the characteristic of “moderate early uplifting, long-term stability and intensive late reformation”. Besides, NE-NNE-trending trough-like folds, high dip-angle thrust faults and strike-slip faults are well-developed in the study area, and the central wide and gentle structure zone has less faults, moderate buried depth and good preservation conditions. In addition, the component of the natural gas and strata water shows that the superior roof, floor and regional cap rocks can effectively retard the gas dissipation and strata water invasion. Finally, an evaluation index system of structural preservation conditions is put forward and applied to identify the favorable preservation zones in the Cen'gong block. © 2016, Editorial Office of Oil and Gas Geology. All right reserved.


Wang R.,China University of Geosciences | Gong D.,China Energy Reserve Corporation | Gong D.,Tongren Sino Energy Natural Gas Corporation | Ding W.,China University of Geosciences | And 5 more authors.
Earth Science Frontiers | Year: 2016

The brittleness determines the fracability of shale gas reservoir, which has a significant impact on shale gas exploration and development. Recently, China has achieved a breakthrough of the Lower Silurian Longmaxi shale in the Sichuan Basin and its surrounding areas. Compared with the Longmaxi shale, the Lower Cambrian Niutitang shale has a great deposition thickness and wide distribution area, which is another significant stratum for China's shale gas. In this paper, the brittleness of Niutitang shale was evaluated and analyzed in the study area based on the data of core mechanical test, array sonic logging, mineral composition and fracture parameters. The results show that the relationship between brittleness and brittle mineral content is not a simple positive correlation. The brittleness and fracability of shale are determined by the content of brittle minerals and TOC (total organic carbon), the degrees of thermal evolution (diagenesis stage) and fracture development. Because of the positive correlation between quartz and TOC contents, when the TOC content is less than 6.5%, the increase in the brittleness caused by the increase in the quartz content is greater than the increase in the ductility caused by the increase in the TOC content; when the TOC content is greater than 6.5%, the ductility increases faster than the brittleness, which results in negative correlations of the brittleness with the TOC and quartz contents and low fracture density in the sections with high TOC content. This understanding will guide the exploration and development of shale gas and is very helpful for optimizing drilling and fracture stimulation intervals in southern China. © 2016, Editorial Office of Earth Science Frontiers. All right reserved.

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