Evolution of overmature marine shale porosity and implication to the free gas volume

Wang, Feiyu; Guan, Jing; Feng, Wei; Bao, Linyan

doi:10.1016/s1876-3804(13)60111-1

Cited by 121 publications

(76 citation statements)

References 10 publications

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“…This portion of gas would be important to the preservation of shale porosity in the very high maturity stage. Porosity data from the North America shale and the Lower Paleozoic shale of the southern area of the Sichuan Basin show an obvious decrease when R o or EqR o is over 3.0 % (Wang et al 2013a), implying that this relationship indeed exists in natural shale systems. Figure 3 further shows that shale porosity varies widely from 3 % to 6 % when R o or EqR o value is between 1.0 % and 3.0 %, without a clear relationship with maturity, which reflects the combined effect of multiple factors (except for maturity), such as TOC content and mineral compositions on shale porosity (Curtis et al 2010;Chalmers and Bustin 2008;Chalmers et al 2012;Ross and Bustin 2009).…”

Section: Geological Characteristics Of the Lower Paleozoic Shalementioning

confidence: 91%

“…The Lower Cambrian and Lower Silurian shales have EqR o values of, respectively, 2.7 %-6.2 % and 1.9 %-3.8 % in the whole Yangtze region (Cheng and Xiao 2013), and 2.5 %-3.5 % and 2.4 %-3.2 % in the Sichuan Basin (Wang et al 2009a;Zou et al 2014). Shale generally has a quite low porosity when it has evolved to the dry gas stage (R o [ 2.0 %) (Wang et al 2013a), but its reservoir properties still change with further increasing maturity (Chen and Xiao 2014). Substantial uplifting and strata denudation reduce the temperature and pressure of a shale system, which will lead to an increase in its fluid pressure coefficient if the system is ideally confined (Zhou et al 2014b).…”

Section: Geological Characteristics Of the Lower Paleozoic Shalementioning

confidence: 99%

“…For instances, this value is approximately 1 % for the Marcellus Shale (R o = 2 %) (Milliken et al 2013) and 1.2 %-1.3 % for the Lower Paleozoic shale (EqR o = 2.0 %-3.1 %) from the southern area of the Sichuan Basin (Wang et al 2013a). Therefore, the development and evolution of organic pores becomes an important factor affecting shale porosity.…”

Section: Geological Characteristics Of the Lower Paleozoic Shalementioning

confidence: 99%

“…Therefore, the development and evolution of organic pores becomes an important factor affecting shale porosity. According to the data from literature, shale porosity has a clear positive correlation with TOC content when TOC is within a definite range (Milliken et al 2013;Pan et al 2015;Tian et al 2013;Wang et al 2013a). However, this positive correlation will be changed or even reversed to be negative when TOC is very high, over this range (Milliken et al 2013;Pan et al 2015;Wang et al 2013a).…”

Section: Geological Characteristics Of the Lower Paleozoic Shalementioning

confidence: 99%

“…According to the data from literature, shale porosity has a clear positive correlation with TOC content when TOC is within a definite range (Milliken et al 2013;Pan et al 2015;Tian et al 2013;Wang et al 2013a). However, this positive correlation will be changed or even reversed to be negative when TOC is very high, over this range (Milliken et al 2013;Pan et al 2015;Wang et al 2013a). The TOC turning point occurs at about 5.6 % for the Marcellus Shale (Milliken et al 2013), 5.0 % for the Lower Paleozoic shale from the southern area of the Sichuan Basin (Wang et al 2013a), and 12 % for the Upper Permian shale from the Lower Yangtze region .…”

Section: Geological Characteristics Of the Lower Paleozoic Shalementioning

confidence: 99%

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Main controlling factors and enrichment area evaluation of shale gas of the Lower Paleozoic marine strata in south China

et al. 2015

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The Lower Paleozoic shale in south China has a very high maturity and experienced strong tectonic deformation. This character is quite different from the North America shale and has inhibited the shale gas evaluation and exploration in this area. The present paper reports a comprehensive investigation of maturity, reservoir properties, fluid pressure, gas content, preservation conditions, and other relevant aspects of the Lower Paleozoic shale from the Sichuan Basin and its surrounding areas. It is found that within the main maturity range (2.5 % \ EqR o \ 3.5 %) of the shale, its porosity develops well, having a positive correlation with the TOC content, and its gas content is controlled mainly by the preservation conditions related to the tectonic deformation, but shale with a super high maturity (EqR o [ 3.5 %) is considered a high risk for shale gas exploration. Taking the southern area of the Sichuan Basin and the southeastern area of Chongqing as examples of uplifted/folded and faulted/folded areas, respectively, geological models of shale gas content and loss were proposed. For the uplifted/folded area with a simple tectonic deformation, the shale system (with a depth [ 2000 m) has largely retained overpressure during uplifting without a great loss of gas, and an industrial shale gas potential is generally possible. However, for the faulted/folded area with a strong tectonic deformation, the sealing condition of the shale system was usually destroyed to a certain degree with a great loss of free gas, which decreased the pressure coefficient and resulted in a low production capacity. It is predicted that the deeply buried shale ([3000 m) has a greater gas potential and will become the focus for further exploration and development in most of the south China region (outside the Sichuan Basin).

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Section: Geological Characteristics Of the Lower Paleozoic Shalementioning

confidence: 91%

Section: Geological Characteristics Of the Lower Paleozoic Shalementioning

confidence: 99%

Section: Geological Characteristics Of the Lower Paleozoic Shalementioning

confidence: 99%

Section: Geological Characteristics Of the Lower Paleozoic Shalementioning

confidence: 99%

Section: Geological Characteristics Of the Lower Paleozoic Shalementioning

confidence: 99%

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Main controlling factors and enrichment area evaluation of shale gas of the Lower Paleozoic marine strata in south China

et al. 2015

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Comparative study of nanoscale pore structure of Lower Palaeozoic marine shales in the Middle‐Upper Yangtze area, China: Implications for gas production potential

et al. 2017

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The Lower Cambrian Niutitang and Lower Silurian Longmaxi shales in the Middle‐Upper Yangtze area are considered the primary shale gas units targeted for development in China. To shed some light on the difference in nanopore structures between Niutitang and Longmaxi shales, systematic comparative investigations were conducted using various techniques, including geochemical analyses, field emission scanning electron microscopy (FE‐SEM), high‐pressure mercury intrusion porosimetry (MIP), and low‐pressure N2/CO2 adsorption techniques. The results show that both Niutitang and Longmaxi shales have high total organic carbon (TOC) content and complex mineral compositions. The porosity of Longmaxi shales is higher than that of Niutitang shales, with an average value of 3.26% and 2.04%, respectively. Interestingly, for both shale formations, the mesopores (2–50 nm) are the major contributors to pore volumes, whereas the specific surface area is dominated by micropores (<2 nm). For the mesopore size distributions (PSDs) calculated from the N2 adsorption, the Longmaxi shales have a dominant pore size ranging from 10 to 60 nm. In contrast, there are more fine mesopores (2–8 nm) in the Niutitang shales. Furthermore, we found that numerous nanoscale pores are well‐developed within graptolite‐derived organic matter (OM) in the Longmaxi shales. These interconnected graptolite periderm pore systems may not only provide a storage space for both adsorbed and free gas but also serve as pathways for gas transport. The Niutitang shales developed relatively fewer OM pores with smaller diameters, lower OM surface porosity, and lower connectivity compared to the Longmaxi shales. The differences in OM pore structure partly explain why there is a large production difference between these two formations.

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Shale Gas Occurrence State

Yang,

2024

Sedimentation and Reservoirs of Marine Shale in South China

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Evolution of overmature marine shale porosity and implication to the free gas volume

Cited by 121 publications

References 10 publications

Main controlling factors and enrichment area evaluation of shale gas of the Lower Paleozoic marine strata in south China

Main controlling factors and enrichment area evaluation of shale gas of the Lower Paleozoic marine strata in south China

Comparative study of nanoscale pore structure of Lower Palaeozoic marine shales in the Middle‐Upper Yangtze area, China: Implications for gas production potential

Shale Gas Occurrence State

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