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.

Analysis of Developmental Characteristics and Dominant Factors of Pore-Fracture Systems in Lower Cambrian Marine Shale Reservoirs: A Case Study of the Niutitang Formation, Fenggang Block, Southern China

2021 ◽  
Vol 21 (1) ◽  
pp. 57-71
Author(s):  
Fu-Hua Shang ◽  
Yan-Ming Zhu ◽  
Hai-Tao Gao ◽  
Yang Wang ◽  
Rui-Yin Liu ◽  
...  
Keyword(s):  
Lower Cambrian ◽  
Sichuan Basin ◽  
Distribution Area ◽  
Strong Positive Correlation ◽  
Longmaxi Formation ◽  
Positive Correlation ◽  
Fracture Systems ◽  
Fracture Development ◽  
The Sichuan Basin ◽  
Niutitang Formation

Due to breakthroughs in the Lower Silurian Longmaxi Formation in the Sichuan Basin and multiple strata around the basin, the northern part of Guizhou adjacent to the Sichuan Basin has become a key area for shale gas exploration. Compared with the Longmaxi Formation, the Niutitang Formation displays greater TOC (total organic carbon) content, depositional thickness and distribution area, but the details remain undetermined. In the study area, the Lower Cambrian Niutitang Formation typically has high TOC content, maturity and brittle mineral content. The study area has experienced multiple periods of tectonic movement, which have great influence on the fracture and pore characteristics. The fractures are mainly structural fractures and have obvious zoning. The primary types of pores are intraparticle pores, organic matter pores, and interparticle pores. Further, macropores and mesopores less than 50 nm contribute most of the pore volume, while pores less than 2 nm contribute most of the specific surface area. Many factors affect the pore-fracture system, such as tectonism, TOC content, mineral composition, and sedimentary environment. Tectonic movements produce fractures based on the changing stress field, but the degree of fracture development does not agree well with the degree of pore development. The TOC content has good positive correlations with the development of fractures and micropores, especially for nanoporosity, while clay minerals show a negative correlation with the development of fractures but a strong positive correlation with the growth of micropores. Quartz displays a positive correlation with the development of fractures but no good correlation with pore development. Finally, the lithofacies, lithologies and mineral compositions under the control of sedimentary environments are internal factors that can impact the development of pore-fracture systems.

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.

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