scholarly journals Compositional and Isotopic Characteristics for The Longmaxi Shale Gas in The Northern Guizhou Area, South China

2020 ◽  
Author(s):  
Wenting Jiang ◽  
Peng Xia ◽  
Qingguang Li ◽  
Yong Fu ◽  
Yuliang Mou
Keyword(s):  
Shale Gas ◽  
Thermal Maturity ◽  
Hydrocarbon Gases ◽  
Longmaxi Formation ◽  
Isotope Distribution ◽  
Lower Silurian ◽  
Longmaxi Shale ◽  
Evolution Stage ◽  
Gaseous Hydrocarbons ◽  
Tectonic Movements

Abstract The organic-rich marine shale of the Lower Silurian Longmaxi formation in the northern Guizhou area (NGA), China, is characterized by its high thermal maturity (Ro values range in 2.18%~3.12%), high TOC values (0.92%~4.87%), high gas contents (0.47~2.69 m3/t) and type II1 organic matter, and has recently been a precursor for shale gas exploration and development. Compositional and isotopic parameters of 7 gas samples from Longmaxi shale from DY-1 well were analyzed in this study. Dry coefficient of the gases is up to 30~200 making the northern Guizhou Longmaxi shale gas among the driest gaseous hydrocarbons in the world. The δ13CCH4 values range from -38.6‰ to -18.6‰ and the δ13CC2H6 values vary in -36.2‰~-30.8‰. These results indicate that the Longmaxi shale gas is of thermogenic origin and oil derived. This Longmaxi shale gas has high proportion of non-hydrocarbon gases especially including nitrogen in response to complicate tectonic movements and strong hydrodynamic flushing. Tectonic movement and hydrodynamic flushing not only destroy hydrocarbon gases reservoirs but also change the isotope distribution of gaseous hydrocarbons. Isotopic reversal is frequent in closed system, and under relatively bad preserving condition, the isotope distribution will back to normal even at overmature evolution stage.

Prospect Analysis of Shale Gas Resource Exploration in the Lower Silurian Longmaxi Formation, Southeastern Margin of the Sichuan Basin, China

2014 ◽  
Vol 1014 ◽  
pp. 228-232 ◽  
Author(s):  
Chen Lin Hu ◽  
Yuan Fu Zhang ◽  
Zhi Feng Wang ◽  
Hai Bo Zhang
Keyword(s):  
Shale Gas ◽  
Sedimentary Environment ◽  
Source Rocks ◽  
Guizhou Province ◽  
Mature Stage ◽  
Carbonaceous Shale ◽  
Thin Sections ◽  
Longmaxi Formation ◽  
Lower Silurian ◽  
Longmaxi Shale

In order to understand the sedimentary characteristics of shale and prospects of shale gas exploration in the lower Silurian Longmaxi Formation northern of Guizhou Province, outcrop and core observations, thin sections, X-ray diffraction analysis and other means are used. Studies show that the thickness of Longmaxi formation shale is generally large, range from 20m to 200m, mainly develop in the water shelf. The mineral mainly compose of detrital quartz and clay minerals, and five lithofacies can be identified: black shale, silty shale, carbonaceous shale, calcareous shale and argillaceous siltstone. Longmaxi shale kerogen type is mainlyIand II, and Ro value is average of 1.87%, mainly in the mature - over mature stage. In addition, the TOC content and gas content of Longmaxi shale is high, what’s more, these two parameters have good positive correlation. Compared with the Barnett shale, both of them have some similarities in the development environment shale, shale thickness and type of organic matter and TOC content, while, Longmaxi shale is deeply buried and post-destruction more intense. Longmaxi shale sedimentary environment is stable, high shale thickness and stable distribution, good quality source rocks and high brittle mineral content, which has meet the basic parameters of shale gas exploration and development, and has a large shale gas exploration potential in study area.

The molecular and carbon isotopic constrains on origin and storage of Longmaxi Formation shale gas in Changning area, Sichuan Basin, China

2015 ◽  
Vol 3 (2) ◽  
pp. SJ35-SJ47 ◽  
Author(s):  
Qingyan Tang ◽  
Mingjie Zhang ◽  
Chunhui Cao ◽  
Zhe Song ◽  
Zhongping Li ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Mass Spectrometry Analysis ◽  
Hydrocarbon Gases ◽  
Longmaxi Formation ◽  
Isotopic Compositions ◽  
Carbon Isotopic ◽  
Longmaxi Shale ◽  
And Storage

We have developed a vacuum-crushing method for the extraction of gases stored in shale for the determination of gas yield, chemical composition, and carbon isotopic composition by online gas-chromatography and mass spectrometry. Analysis of the evacuation and parallel experiments showed low standard deviation and good reproducibility. This approach significantly improved the detection limits for trace-gas analysis in shale and measured multiple nonhydrocarbon gas components in a single run. We analyzed the chemical and carbon isotopic compositions of the gases released by one-step vacuum crushing from nineteen samples of organic-rich Longmaxi Formation (Fm.) shale in Changning outcrop, Sichuan Basin, China, and we studied the main controls on gas chemistry of retained gas in the Longmaxi Shale. The results showed that the crushed gas is high in [Formula: see text] and [Formula: see text] but low in [Formula: see text]. The crushed gas has obviously lower [Formula: see text] ratios than the gas produced from the Longmaxi Fm. after hydraulic fracturing; it was dominated by [Formula: see text] gas while it is normalized to 100% total gaseous hydrocarbons and similar in chemical composition to hydrocarbon gases in the produced gas. Yields of [Formula: see text], [Formula: see text], and [Formula: see text] in the crushed gas of most samples showed a weak positive correlation with total organic carbon (TOC) contents. The crushed gas had significantly light [Formula: see text] (on average [Formula: see text]) values and similar [Formula: see text] values when compared with the produced gas in the Changning area. The [Formula: see text] values of [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] have similar features to the produced gas from the Weiyuan shale-gas play. Isotopically reversed trends ([Formula: see text]) between ethane and methane were observed for some samples. Our findings regarding the similarity in chemical and carbon isotopic compositions between crushed gas and produced gas from the Weiyuan shale-gas play might provide important evidence of the origin and storage of shale gas in the organic-rich Silurian Longmaxi Fm.

scholarly journals Reservoir Characteristics of the Lower Silurian Longmaxi Shale in Zhaotong Region, Southern China

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Chao Luo ◽  
Nanxin Yin ◽  
Hun Lin ◽  
Xuanbo Gao ◽  
Junlei Wang ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Total Organic Carbon ◽  
Shale Gas ◽  
Southern China ◽  
Gas Content ◽  
High Quality ◽  
Longmaxi Formation ◽  
Lower Silurian ◽  
Longmaxi Shale ◽  
Scanning Electron

The lower Silurian Longmaxi Formation hosts a highly productive shale gas play in the Zhaotong region of southern China. According to core observation, X-ray diffraction analyses, and scanning electron microscopy (SEM) observations, the shale comprises primarily quartz, carbonate minerals, and clay minerals, with minor amounts of plagioclase, K-feldspar, and pyrite. The clay mineral content ranges from 15.0% to 46.1%, with an average of 29.3% in the Zhaotong region. Organic geochemical analyses show that the Longmaxi Formation has good potential for shale gas resources by calculating total organic carbon, vitrinite reflectance, and gas content. Scanning electron microscope images demonstrate that reservoir pore types in the Longmaxi shale include organic pores, interparticle pores, intercrystalline pores, intraparticle pores, and fractures. Reservoir distribution is controlled by lithofacies, mineral composition, and geochemical factors. In addition, we investigated the relationships between reservoir parameters and production from 15 individual wells in the Zhaotong region by correlation coefficients. As a result, the brittleness index, total organic carbon (TOC), porosity, and gas content were used to define high-quality reservoirs in the Longmaxi shale. Based on these criteria, we mapped the thickness and distribution of high-quality reservoirs in the Longmaxi Formation and selected highlighted several key sites for future exploration and development.

scholarly journals Total Porosity Measured for Shale Gas Reservoir Samples: A Case from the Lower Silurian Longmaxi Formation in Southeast Chongqing, China

Minerals ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 5 ◽  
Author(s):  
Fangwen Chen ◽  
Shuangfang Lu ◽  
Xue Ding ◽  
Hongqin Zhao ◽  
Yiwen Ju
Keyword(s):  
Shale Gas ◽  
Clay Content ◽  
Total Porosity ◽  
Gas Reservoir ◽  
Longmaxi Formation ◽  
Fine Grained ◽  
Average Value ◽  
Lower Silurian ◽  
Shale Gas Reservoir ◽  
Research Institute

Measuring total porosity in shale gas reservoir samples remains a challenge because of the fine-grained texture, low porosity, ultra-low permeability, and high content of organic matter (OM) and clay mineral. The composition content porosimetry method, which is a new method for the evaluation of the porosity of shale samples, was used in this study to measure the total porosity of shale gas reservoir samples from the Lower Silurian Longmaxi Formation in Southeast Chongqing, China, based on the bulk and grain density values. The results from the composition content porosimetry method were compared with those of the Gas Research Institute method. The results showed that the composition content porosimetry porosity values of shale gas reservoir samples range between 2.05% and 5.87% with an average value of 4.04%. The composition content porosimetry porosity generally increases with increasing OM and clay content, and decreases with increasing quartz and feldspar content. The composition content porosimetry results are similar to the gas research institute results, and the differences between the two methods range from 0.05% to 1.52% with an average value of 0.85%.

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