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Zhang C.-C.,Petrochina | Wang Y.-M.,Petrochina | Dong D.-Z.,Petrochina | Dong D.-Z.,National Energy Shale Gas periment Center | Guan Q.-Z.,Petrochina
Natural Gas Geoscience | Year: 2016

Brittleness is significant for geological evaluation of shale-gas reservoirs. Based on outcrop and drilling data, this paper first proposed a new brittleness index, which use quartz, dolomite and pyrite as brittle components, and evaluated the brittleness of Wufeng-Longmaxi shale in Changning region, Southern Sichuan combined with the elastic parameters-based index. And then we analyzed the relationship between brittleness and mineral composition, TOC. Applying "ternary diagram combined with depositional microfacies" method to classify the lithofacies types of Wufeng-Longmaxi shale, we further selected the "sweet spot" layer on the basis of favorable lithofacies according to previous studies. The results showed that: (1)The lower part of Wufeng-Longmaxi shale, with appropriate thickness of 30-40m, has the best brittleness characteristics: mineral-based brittleness index of 50%-75%, Young's Modulus of 37.84GPa, Poisson's Ratio of 0.19, and average elastic parameters-based brittleness index of 61%. And the brittleness index decreases upward. (2)Brittleness index correlates well with mineral composition and TOC, reflecting the control of depositional environment on shale brittleness. (3)Siliceous and calcareous-siliceous shale deposited in deep-water shelf, which were developed in Wufeng to the middle-lower part of Rhuddanian with average brittleness index>50%, average TOC>3% and total thickness of appropriately 42m, are "sweet spot" layer in Changning region. © 2016, Science Press. All right reserved.

Guan Q.-Z.,Petrochina | Dong D.-Z.,Petrochina | Dong D.-Z.,National Energy Shale Gas periment Center | Wang S.-F.,Petrochina | And 3 more authors.
Natural Gas Geoscience | Year: 2016

n order to analyze microstructural characteristics of shale reservoirs from marine and lacustrine facies and discuss the differences and their influencing factors, Ar-ion milling-Scanning Electron Microscopy (Ar-SEM), N2 adsorption test, nuclear magnetic resonance (NMR) and mathematical statistics are used to study two facies sediments from qualitative and quantitative aspects. Three obvious results are found: (1) Marine facies shale reservoirs mainly have developed inter-particle pores and organic matter pores in matrix-related pores, but lacustrine facies shale have more non-organic pores; (2) Pore size of marine facies shale reservoirs is smaller than the lacustrine ones, but they have more BET and BJH; (3) Geological micro-fractures are more developed in the marine facies shale reservoirs, the lacustrine ones mainly contain more micro-fractures between clay layers. Mineral constituents, organic matter types, thermal maturity and tectonic activity times are key factors to affect the differences on microstructural characteristics of two facies shale reservoirs. © 2016, Science Press. All right reserved.

Zhou S.,Petrochina | Zhou S.,China National Petroleum Corporation | Zhou S.,National Energy Shale Gas periment Center | Xue H.,Petrochina | And 8 more authors.
Zhongguo Shiyou Daxue Xuebao (Ziran Kexue Ban)/Journal of China University of Petroleum (Edition of Natural Science) | Year: 2016

In order to measure the shale permeability more effectively and quickly, 22 shale samples from Lower Silurian Longmaxi Formation in southern Sichuan Basin were collected and used in the low field nuclear magnetic resonance (NMR) and high-speed centrifugal experiments. The results show that the relative error of the four rocks NMR permeability model currently used are very large, and is small only in the extended SDR model. Therefore the four conventional NMR models are not suitable for the NMR permeability calculation of shale. In order to reduce the calculation error, a single parameter model of shale NMR permeability is set up based on the SDR model. The correlation coefficient of this new model reaches 0.967, and the average relative error of pulse decay permeability is about 18.31%. It is concluded that the new model can calculate the permeability of gas shale more accurately, which provides a fast, nondestructive and effective experimental methodology for shale permeability test. © 2016, University of Petroleum, China. All right reserved.

Liang F.,China University of Mining and Technology | Liang F.,National Energy Shale Gas periment Center | Liang F.,Petrochina | Liang F.,Key Laboratory of Unconventional Oil & Gas | And 15 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2015

Based on outcrops and core data, the sedimentary distribution and reservoir characteristics of shale gas reservoir of Niutitang formation in Northwest Hunan were studied by analyzing sedimentology, mineralogy and organic chemistry. Seven major lithofacies and a basis of sedimentary microfacies classification of Niutitang shale have been divided by using X ray diffraction data, sedimentary structure, lithofacies characteristics and organic matter content. The sedimentary subfacies is divided into deep shelf facies, bathyal shelf facies and shallow shelf facies, and the geochemical condition of deep-water shelf facies is the most favorable facies for the development of organic rich shale. The average porosity of shale is 3.8% and the reservoir space of shale is mainly composed of matrix pore, of which the pore diameter is less than 50 nm. The fracture of shale is filled with calcite which made no contribution to effective reservoir space for shale gas storage and even made a certain damage for shale gas preservation. N2 adsorption and SEM analysis results show that the development of shale pore is influenced by many factors. There is an increasing tendency for total pore volume if the contents of TOC, clay minerals and pyrite are increasing, but the correlation coefficient is low. It is worth noting that the correlation coefficient between pyrite and pore volume is relatively high which shows that the pyrite plays a positive role for the development of shale pore. The adsorption ability of rich organic shale is strong, which is mainly controlled by TOC. © 2015, China Coal Society. All right reserved.

Zou C.,Petrochina | Dong D.,Petrochina | Dong D.,National Energy Shale Gas periment Center | Wang Y.,Petrochina | And 17 more authors.
Shiyou Kantan Yu Kaifa/Petroleum Exploration and Development | Year: 2016

This paper mainly discusses the industrialization progress, "sweet spot" evaluation criterion, E&P technologies, success experiences, challenges and prospects of China's shale gas. Based on the geologic and engineering parameters of the Fuling, Changning and Weiyuan shale gas fields in the Sichuan Basin, this paper points out that China's shale gas has its particularity. The discoveries of super-giant marine shale gas fields with high evolution degree (Ro=2.0%-3.5%) and ultrahigh pressure (pressure coefficient=1.3-2.1) in southern China is of important scientific significance and practical value to ancient marine shale gas exploration and development to China and even the world. It's proposed that shale gas "sweet spots" must be characterized by high gas content, excellent frackability and good economy etc. The key indicators to determine the shale gas enrichment interval and trajectory of horizontal wells include "four highs", that is high TOC (>3.0%), high porosity (>3.0%), high gas content (>3.0 m3/t) and high formation pressure (pressure coefficient>1.3), and "two well-developed" (well-developed beddings and well-developed micro-fractures). It's suggested that horizontal well laneway be designed in the middle of high pressure compartment between the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation. The mode of forming "artificial shale gas reservoir" by "fracturing micro-reservoir group" is proposed and the mechanism of "closing-in after fracturing, limiting production through pressure control" is revealed. Several key technologies (such as three-dimensional seismic survey and micro-seismic monitoring of fracturing, horizontal wells, "factory-like" production mode, etc.) were formed. Some successful experiences (such as "sweet spot" selection, horizontal well laneway control, horizontal length optimization and "factory-like" production mode, etc.) were obtained. The four main challenges to realize large-scale production of shale gas in China include uncertainty of shale gas resources, breakthroughs in key technologies and equipment of shale gas exploration and development below 3 500 m, lower cost of production, as well as water resources and environment protection. It is predicted that the recoverable resources of the Lower Paleozoic marine shale gas in southern China are approximately 8.8×1012 m3, among which the recoverable resources in the Sichuan Basin are 4.5×1012 m3 in the favorable area of 4.0×104 km2. The productivity of (200-300)×108 m3/a is predicted to be realized by 2020 when the integrated revolution of "theory, technology, production and cost" is realized in Chinese shale gas exploration and development. It is expected in the future to be built "Southwest Daqing Oilfield (Gas Daqing)" in Sichuan Basin with conventional and unconventional natural gas production. © 2016, Science Press. All right reserved.

Liang F.,China University of Mining and Technology | Liang F.,Petrochina | Liang F.,National Energy Shale Gas periment Center | Liang F.,China National Petroleum Corporation | And 27 more authors.
Shiyou Kantan Yu Kaifa/Petroleum Exploration and Development | Year: 2016

The shale gas enrichment pattern of Well Wuxi-2 in northeast Chongqing was studied, based on the data of the drilling, graptolite biostratigraphy, geochemistry, rock minerals, microscopic characteristics of reservoir beds and tectonic conditions, etc. The organic-rich shale of Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation is 89.8 m thick in Well WX-2. The graptolite biozonations are completely developed in this well, and the organic-rich shale intervals extend upward from the late Katian of the Ordovician to the early Telychian of the Lower Silurian. The deposition time of the organic-rich shale is far longer and the thickness is larger than those in other areas of the Sichuan Basin. The highest measured gas content exceeded 8 m3/t in Well WX-2, and the gas content is mainly controlled by TOC. The organic nano-pores are the main storage space, and the minerals contribute less to the storage space. The organic pores larger than 50 nm are well-developed and those less than 10 nm are the main reservoir space of adsorbed gas. The target intervals of Well WX-2 are located under the neutral surface of compressional Tianba anticline. Two vertical fracture (cleavage) development zones, which are beneficial for shale gas storage and complex fracture network formation during later fracturing, were formed in brittle layers of this organic-rich shale. Compressional faults existed in two limbs of the Tianba anticline, with non-permeable shale developing on both sides of fault planes and development of clay smear, which shows that the faults have good sealing properties, and are favorable for shale gas preservation. Thus the good match between the above various accumulation conditions forms the "tectonic sweet-spot" of shale gas in this study area. © 2016, The Editorial Board of Petroleum Exploration and Development. All right reserved.

Guo W.,Petrochina | Hu Z.,Petrochina | Zuo L.,Petrochina | Gao S.,Petrochina | And 4 more authors.
Lixue Xuebao/Chinese Journal of Theoretical and Applied Mechanics | Year: 2015

Gas desorption-diffusion-seepage coupled experiment was designed and carried out with Longmaxi shale samples collected from South of Sichuan, and both the gas flow characteristics and pressure propagation were then obtained. Shale gas desorption-diffusion-seepage coupling mathematical model was derived and numerical solution of the mathematical model using finite difference method was obtained. Numerical simulation results compared with the experimental results show that the model can well describe the gas transport in the shale matrix. And shale matrix permeability, diffusion coefficient, desorption constants and other factors can affect the gas flow through shale matrix as well as pressure propagation, which should be taken into consideration in the development of shale gas reservoir. The presented mathematical model provides a new method to calculate the production capability of shale gas well. © 2015, Editorial Office of Chinese Journal of Theoretical and Applied Mechanics. All right reserved.

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