Further research on chlorite rims in sandstones: evidence from the Triassic Yanchang Formation in the Ordos basin, China
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ORIGINAL PAPER
Further research on chlorite rims in sandstones: evidence from the Triassic Yanchang Formation in the Ordos basin, China Fang Xiang 1,2 & Yuwan Wang 2 & Qin Feng 2 & Deyan Zhang 2 & Junxing Zhao 1,2
Received: 26 December 2014 / Accepted: 26 May 2016 # Saudi Society for Geosciences 2016
Abstract Chlorite rims are the most common type of authigenic chlorite in sandstones, and attract particular attention because they are always found in high-quality sandstone reservoirs. This study researches chlorite rims in sandstones of the Chang 9 oil-bearing member of the Triassic Yanchang Formation in the Ordos basin, China. Using casting thin sections, a scanning electron microscope and porosity–permeability data, the following issues were addressed: (1) the formation stage of chlorite rims, (2) the relationship of chlorite rim formation to other diagenetic features, and (3) the relationship of chlorite rims with sandstone reservoir quality. From the results, the following conclusions can be drawn: (1) chlorite rims form during the A–B phase of eodiagenesis, (2) chlorite rims cannot enhance the mechanical strength of rocks and their ability to resist compaction, (3) the reason that chlorite rims inhibit quartz secondary enlargement is a change in pH and silica concentration leading to the cessation of quartz growth. However, chlorite rims have no relationship with the formation of later idiomorphic authigenic quartz; (4) chlorite rims cannot enhance the reservoir quality of sandstone, but can be an indicator of high primary intergranular porosity.
* Fang Xiang [email protected]
1
State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China
2
Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China
Keywords Chlorite rim . Diagenetic stage . Compaction . Quartz cementation . Reservoir quality
Introduction Authigenic chlorite is a common type of clay cement in clastic rocks, and is found widely in marine and lacustrine sandstones (Baker et al. 2000; Billault et al. 2003; Huang et al. 2004; Berger et al. 2009; Gong et al. 2011). Pore-lining chlorite is the most important type of authigenic chlorite and is common in sandstone reservoirs of Mesozoic and Cenozoic continental petroliferous basins in China. This type of cement has attracted particular attention because of its close relationship with reservoir porosity (Huang et al. 2004). From previous studies, there is general agreement on the depositional environment, pore water properties, and material sources of porelining chlorite. However, there are still some uncertainties about certain aspects of pore-lining chlorite, as discussed below. First, the formation stage of pore-lining chlorite is still uncertain. Although it is generally believed that pore-lining chlorite forms during the early phase of eodiagenesis (Huang et al. 2004), it is also thought that it is a product of the telodiagenetic stage (Zhong et al. 1996), the syndepositional period (Yao et al
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