Well logging evaluation of the shale gas potential in the lower Silurian Longmaxi Formation, Weiyuan, southern Sichuan Basin, China

2021 ◽  
pp. 1-64
Author(s):  
Guangzhao Zhou ◽  
Zhiming Hu ◽  
Xiangui Liu ◽  
Xianggang Duan ◽  
Jin Chang
Keyword(s):  
Spatial Distribution ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Vitrinite Reflectance ◽  
Well Logging ◽  
Carbonaceous Shale ◽  
Organic Carbon Content ◽  
Type I ◽  
Longmaxi Formation ◽  
Marine Shale

Recent observations of shale gas breakthroughs have in the Weiyuan marine shale gas play in the Sichuan Basin have attracted great interest. To better understand these breakthroughs, we use core description, FIB-SEM data, XRD data, organic geochemistry, and well logging data, to better understand the reservoir characteristics carbonaceous shale, calcareous shale, and siliceous shale lithology, with a focus on the organic-rich shale units. We find conventional well log methods are effective in mapping the spatial distribution of the organic-rich shale in the Weiyuan area where the. total organic carbon content in the Longmaxi Formation ranges from 1.35%-6.95%, averaging 4.42%. The kerogen is Type I-II and the vitrinite reflectance (Ro) is greater than 2.57%, which indicates that the formation is susceptible to shale gas accumulation. The clay mineral content ranges from 48 wt.% to 63 wt.% (avg. 51 wt.%).with illite and chlorite averaging 73.8% and 25.7%, respectively. The brittle mineral quartz and plagioclase content ranges from 32 wt.% to 61 wt.% (avg. 47 wt.%). Compared to the surrounding litholgic units, the marine shale exhibits relatively high GR, CNL, AC, RT, K, and U values and relatively low DEN, PE and Th/U values, allowing us to construct. Cross-plots to define the units of interest. Using the same process, we quantify the TOC content providing a spatial distribution of organic-rich shale using conventional well logging.

scholarly journals A Comparative Study of the Micropore Structure between the Transitional and Marine Shales in China

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Pengfei Jiao ◽  
Genshun Yao ◽  
Shangwen Zhou ◽  
Zhe Yu ◽  
Shiluo Wang
Keyword(s):  
Natural Gas ◽  
Shale Gas ◽  
Ordos Basin ◽  
Organic Carbon Content ◽  
Type I ◽  
Gas Generation ◽  
Longmaxi Formation ◽  
Micropore Structure ◽  
Marine Shale ◽  
Longmaxi Shale

To compare the micropore structure of marine-continental transitional shale with marine shale, organic geochemical, field emission scanning electron microscopy, and low-temperature nitrogen adsorption experiments were conducted on shale samples from the Shanxi Formation in the eastern Ordos Basin and the Longmaxi Formation in the southern Sichuan Basin. The results show that Shanxi Formation shale has a smaller specific surface area and pore volume than Longmaxi Formation shale; therefore, the transitional shales fail to provide sufficient pore spaces for the effective storage and preservation of natural gas. Both the transitional and marine shales are in an overmature stage with high total organic carbon content, but they differ considerably in pore types and development degrees. Inorganic pores and fractures are dominantly developed in transitional shales, such as intragranular pores and clay mineral interlayer fractures, while organic nanopores are rarely developed. In contrast, organic pores are the dominant pore type in the marine shales and inorganic pores are rarely observed. The fractal analysis also shows that pore structure complexity and heterogeneity are quite different. These differences were related to different organic types, i.e., type I of marine shale and type III of transitional shale. Marine Longmaxi shale has experienced liquid hydrocarbon cracking, gas generation, and pore-forming processes, providing good conditions for natural gas to be preserved. However, during the evolution of transitional Shanxi shale, gas cannot be effectively preserved due to the lack of the above evolution processes, leading to the poor gas-bearing property. The detailed comparison of the micropore structure between the transitional and marine shales is of great importance for the future exploitation of marine-continental transitional shale gas in China.

Logging Evaluation Method and its Application for Measuring the Total Organic Carbon Content in Shale

2014 ◽  
Vol 962-965 ◽  
pp. 51-54
Author(s):  
Zhi Feng Wang ◽  
Yuan Fu Zhang ◽  
Hai Bo Zhang ◽  
Qing Zhai Meng
Keyword(s):  
Organic Carbon ◽  
Total Organic Carbon ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Evaluation Method ◽  
Organic Carbon Content ◽  
Geochemical Analysis ◽  
Data Logging ◽  
Longmaxi Formation ◽  
Sedimentary Structures

The acquisition of the total organic carbon (TOC) content mainly relies on the geochemical analysis and logging data. Due to geochemical analysis is restricted by coring and experimental analysis, so it is difficult to get the continuous TOC data. Logging evaluation method for measuring TOC is very important for shale gas exploration. This paper presents a logging evaluation method that the shale is segmented according to sedimentary structures. Sedimentary structures were recognized by core, thin section and scanning electron microscope. Taking Wufeng-Longmaxi Formation, Silurian, Muai Syncline Belt, south of Sichuan Basin as research object, the shale is divided into three kinds: massive mudstone, unobvious laminated mudstone, and laminated mudstone. TOC within each mudstone are calculated using GR, resistivity and AC logging data, and an ideal result is achieved. This method is more efficient, faster and the vertical resolution is higher than △logR method.

scholarly journals Prediction of Fracture Toughness in the Shale Formation Based on Well Logging and Seismic Data: A Case Study of the Lower Silurian Longmaxi Formation in the Sichuan Basin, China

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-13 ◽  
Author(s):  
Kaiyuan Liu ◽  
Jian Xiong ◽  
Xi Zhang ◽  
Xiao Fan ◽  
Le Li
Keyword(s):  
Fracture Toughness ◽  
Spatial Distribution ◽  
Sichuan Basin ◽  
Well Logging ◽  
Distribution Area ◽  
Distribution Characteristics ◽  
Longmaxi Formation ◽  
Lower Silurian ◽  
Shale Formation ◽  
The Sichuan Basin

The rock physics experiments and fracture toughness tests of shales from the Lower Silurian Longmaxi Formation in the Sichuan Basin in China were carried out. Based on this, the calculation model of the fracture toughness was constructed, thus, the single well evaluation of the fracture toughness in shale formation would be obtained based on the well logging data, which can be used to summarize the spatial distribution characteristics of the fracture toughness in the shale formation. However, it is difficult to obtain transverse distribution characteristics of fracture toughness in shale formation based solely on the well logging data. Therefore, in order to investigate the spatial distribution of the fracture toughness, jointing well logging and seismic method could be adopted to quantitatively predict the fracture toughness in shale formation. The results show that fracture toughness of shales is sensitive to acoustic interval transit time and wave impedance. The prediction model of the fracture toughness of shales was constructed, which had a good prediction effect. The fracture toughness values of shales from the Upper Silurian Wufeng-Longmaxi Formation were larger, whereas those of shales from the Lower Silurian Wufeng-Longmaxi Formation were lower. The fracture toughness is mainly distributed in strips along the vertical direction while the distribution area is continuous in the lateral direction, indicating that it has obvious stratification characteristics.

scholarly journals Classification and Evaluation on Shale Gas Reservoir for Wufeng-Longmaxi Formation in Chuannan Area, Sichuan Basin

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 1) ◽  
Author(s):  
Jianlin Guo ◽  
Chengye Jia ◽  
Dongbo He ◽  
Fankun Meng
Keyword(s):  
Shale Gas ◽  
Sichuan Basin ◽  
Gas Content ◽  
Brittleness Index ◽  
Type I ◽  
Gas Reservoir ◽  
Longmaxi Formation ◽  
Positive Correlation ◽  
Gas Saturation ◽  
Shale Gas Reservoir

Abstract Based on the comprehensive statistic and analysis on some representative geological and physical data, the classification criteria on net pay for shale gas reservoir of the Wufeng-Longmaxi formation in Shunan area, Sichuan Basin, are proposed, which include porosity (φ), gas saturation (Sg), density of rock (DEN), brittleness index (BI), and gas content (Vt). When the porosity, gas saturation, brittleness index, and gas content are larger than 3%, 30%, 40%, and 1 m3/t, respectively, and the density of rock is lower than 2.7 g/cm3, then this formation can be seen as the net pay. The application of two key parameters, gas content and brittleness index, could reflect the reservoir resource basis and fracability, respectively. The gas content has a positive correlation with porosity and total organic volume, and the brittleness index has a positive correlation with siliceous and carbonate content. According to the range of these two parameters, the net pay can be classified into three types. For type I, the gas content and brittleness index are larger than 4 m3/t and 50%, respectively. For type II, either the gas content or the brittleness index is lower than 4 m3/t and 50%. For type III, the gas content should be larger than 1 m3/t and lower than 4 m3/t, and the brittleness index is between 40% and 50%. The field application case indicates that the Wufeng formation and low member of the Longmaxi formation have good quality and mainly consist of type I and II formations. In addition, it is found that there is a positive correlation between the penetration ratio for type I formation and the testing production and estimate ultimate recovery (EUR). While this ratio is larger than 50%, the testing production rate and EUR will be over 15×104 m3/d and 8000×104 m3 with a probability of 92%, which meet the requirement of exploitation with reasonable economic benefits.

scholarly journals Deflating the shale gas potential of South Africa’s Main Karoo basin

2017 ◽  
Vol 113 (9/10) ◽  
Author(s):  
Michiel de Kock ◽  
Nicolas Beukes ◽  
Elijah Adeniyi ◽  
Doug Cole ◽  
Annette Götz ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Total Organic Carbon ◽  
Shale Gas ◽  
Vitrinite Reflectance ◽  
Gas Content ◽  
Carbonaceous Shale ◽  
Organic Carbon Content ◽  
Hydrocarbon Generation ◽  
Developmental Potential ◽  
Karoo Basin

The Main Karoo basin has been identified as a potential source of shale gas (i.e. natural gas that can be extracted via the process of hydraulic stimulation or ‘fracking’). Current resource estimates of 0.4–11x109 m3 (13–390 Tcf) are speculatively based on carbonaceous shale thickness, area, depth, thermal maturity and, most of all, the total organic carbon content of specifically the Ecca Group’s Whitehill Formation with a thickness of more than 30 m. These estimates were made without any measurements on the actual available gas content of the shale. Such measurements were recently conducted on samples from two boreholes and are reported here. These measurements indicate that there is little to no desorbed and residual gas, despite high total organic carbon values. In addition, vitrinite reflectance and illite crystallinity of unweathered shale material reveal the Ecca Group to be metamorphosed and overmature. Organic carbon in the shale is largely unbound to hydrogen, and little hydrocarbon generation potential remains. These findings led to the conclusion that the lowest of the existing resource estimates, namely 0.4x109 m3 (13 Tcf), may be the most realistic. However, such low estimates still represent a large resource with developmental potential for the South African petroleum industry. To be economically viable, the resource would be required to be confined to a small, well-delineated ‘sweet spot’ area in the vast southern area of the basin. It is acknowledged that the drill cores we investigated fall outside of currently identified sweet spots and these areas should be targets for further scientific drilling projects.

Gas-prospective area optimization for Silurian shale gas of Longmaxi Formation in southern Sichuan Basin, China

2015 ◽  
Vol 3 (2) ◽  
pp. SJ49-SJ59 ◽  
Author(s):  
Jiang Yuqiang ◽  
Zhang Qichen ◽  
Zhang Hu ◽  
Gan Hui ◽  
Luo Mingsheng ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Integrated Approach ◽  
In Situ Stress ◽  
Data Set ◽  
Longmaxi Formation ◽  
Marine Shale ◽  
Shale Reservoirs

We investigated the development of a new criterion to quantify and rank marine shale reservoirs of the Lower Silurian Longmaxi Formation and to identify the most prospective area in the southern Sichuan Basin by examining the correlation of various parameters and forming a regionally consistent set. These reliable parameters in our model included geologic factors (rock properties), engineering factors (rock brittleness, in situ stress, and pressure gradient), and topographic factors (pipeline availability and land accessibility). In addition to the common parameters (thickness, depth, porosity, and gas in place), our system used some critical factors associated with complex tectonic evolution and gas preservation in detail, such as in situ stress, pressure gradient, and topographic conditions. An integrated data set was used for designing the well trajectory, creating large volume-induced fractures networks, and increasing the initial production of shale gas. Our integrated approach was used to classify into three ranking levels of Silurian Longmaxi marine shale reservoirs in the Changning area in the southern Sichuan Basin. The integrated approach incorporated a prediction model of pressure gradient and the distribution of in situ stress. The initial production from horizontal wells resulted in a positive assessment as high-performing affordable wells, and served as validation of the methodology used to rank prospective areas.

Accumulated Conditions of Shale Gas in the Middle-Low Palaeozoic, Yangtze Platform, China

2012 ◽  
Vol 524-527 ◽  
pp. 122-125 ◽  
Author(s):  
Hai Yan Hu ◽  
Zhen Duo He ◽  
Bao Cai Chen
Keyword(s):  
Organic Matter ◽  
Source Rock ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Thermal Evolution ◽  
Vitrinite Reflectance ◽  
Michigan Basin ◽  
Longmaxi Formation ◽  
San Juan Basin ◽  
Maturity Degree

Shale gas is an important unconventional natural gas resource. There is probably abundant shale gas resource in the Longmaxi Formation of the lower Silurian, Sichuan Basin, West China. Longmaxi Formation is high quality source rock, its TOC(total organic carbon) up to the most vulue 6.5 percent; the Formation more than 1percent TOC is up to 105 meters. Because of high maturity, it cannot identify the kerogen type by element Carbon and Hydron ratio, rather than carbon isotopic value. The isotopic carbon values of Kerogens are more than 29.67 permillage, which showed One Type Kerogen. In the Longmaxi Formation, source rock is up to post maturity and lack of vitrinite, so vitrinite reflectance cannot measure the source maturity. It can measure bitumen reflectance, then calculate relevant vitrinite reflectance (Ro) by bitumen reflectance to identify the organic matter thermal evolution degree. The result showed the maturity degree of organic matter equal to more than 3 percent vitrinite reflectance (Ro), which showed the source rock yielded rich thermogenic gas during the geological thermal evolution. The source rock of Longmaxi Formation has some silt partly composed of quartz mineral, up to 40 percent, which is beneficial to gas reservoir. So, it has available shale gas developed elements because of rich organic matter, high thermal maturity degree, good pool. The geological analogy method is used to assess the resource potential. Sichuan Basin has drastically similar to Michigan Basin and San Juan Basin in basin type, seal conditions, reservoir states, source rock, matched condition and so on. So they are selected as standard basin. Sixteen parameters are used to appraise the shale gas pool geological conditions. Compared with Michigan Basin and San Juan Basin by analogy method, Longmaxi Formation shale gas potential is 0.06-0.36 billion cubic meter per square kilometer.

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