Diagenetic differences in tight sandstone reservoirs in two delta fronts: an example from the Chang 4 and 5 members of t
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ORIGINAL PAPER
Diagenetic differences in tight sandstone reservoirs in two delta fronts: an example from the Chang 4 and 5 members of the Yanchang Formation in the Longdong area, Ordos Basin, China Shifa Zhu 1,2 & Xiaomin Zhu 1,2 & Jiahao Chen 1,2 & Zhen Yang 1,2 & Ye Jia 1,2 & Hang Cui 1,2 Received: 24 August 2018 / Accepted: 9 November 2018 # Saudi Society for Geosciences 2018
Abstract With the intensification of oil and gas exploration, tight sandstone reservoirs have received an increasing amount of attention, particularly with regard to the genesis of tight reservoir rock. The Upper Triassic Yanchang Formation in the Longdong area of the Ordos Basin has developed a typical tight, oil-bearing, clastic reservoir (lithic arkose and feldspathic litharenite, grain size is mainly 0.1~0.3 mm in diameter). During the depositional period of the Chang 4 and 5 members, the two provenance systems of the southwest and northeast developed in the study area. In the southwest, sandstones in the lower part of distributary channels are coarser with fewer quartz overgrowth and ankerite and better reservoir quality (porosity about 12%, permeability about 1 mD). In the northeast, chlorite coating is thicker (> 4 vol%) in the underwater channel sandstones (porosity is about 14%, permeability is about 2 mD) than in the mouth bar sandstones. Sandstones in the upper part of distributary channels are finer with lower permeability (about 0.1 mD). Authigenic ankerite mainly appears around detrital dolomite as an overgrowth. The SiO2 in the quartz overgrowth most likely came from the transformation of smectite to illite and the dissolution of feldspar. In the northeast, only 2 vol% of chlorite rims significantly inhibited quartz overgrowth, but they probably blocked and delayed the dissolution of feldspars by acids. We present results here that show the diagenetic differences in sand bodies in delta fronts are influenced by sediment size, maturity, and the composition of framework grain; the materials that compose authigenic minerals mainly come from the alteration of sandstones. As a whole, the formation of tight reservoir rocks in the study area is closely related to sedimentary facies, composition of framework grain, cement type and content, and development of dissolution. Keywords Tight sandstone . Authigenic minerals . Quartz overgrowth . Chlorite . Ankerite . Ordos Basin
Introduction Unconventional and tight sandstone reservoirs have received increasing attention for oil and gas exploration in recent years (Shanley et al. 2004; Christophe et al. 2013). Tight sandstone Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12517-018-4048-7) contains supplementary material, which is available to authorized users. * Shifa Zhu [email protected] 1
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China
2
College of Geosciences, China University of Petroleum, Beijing 102249, China
reservoirs usually indicate reservoir rock with low
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