Diagenetic Heterogeneity of Deep Sandstones and Its Relationship to Oil Emplacement: A Case Study from the Middle Jurassic Toutunhe Formation in the Fukang Sag, Central Junggar Basin (NW China)

Figure 6

Thin section images and core photographs of sandstones (pore space is highlighted in blue). ((a) and (b)) Sample 4959.8 m, well D-1, plane-polarized light (PPL), and cross-polarized light (XPL), respectively: the predominance of volcanic rock fragments with various igneous textures. Note that some volcanic rock fragments exhibit a typical characteristic alteration of matrix to clays. (c) Sample 4939.73 m, well D-1, and XPL: volcanic and metamorphic rock fragments deformed between detrital quartz and feldspar grains and smeared on the surfaces of these rigid detrital grains. (d) Sample 4425.1 m, well D-8, and PPL: altered and deformed volcanic and metamorphic rock fragments. (e) Sample 4548.5 m, well D-8: calcite commonly forming white concretions in cores. ((f) and (g)) Sample 4548.5 m, well D-8, PPL, and CL, respectively: calcite representing a poikilotopic texture and local replacement of framework grains. The calcite exhibits orange-red luminescence emission. (h) Sample 4138.03 m, well D-7, and PPL: primary intergranular porosity. (i) Sample 4514.65 m, well D-7, and PPL: primary intergranular porosity and chlorite coats. Partial dissolution along the detrital grain margins is frequently observed. (j) Sample 4837.5 m, well D-1, and PPL: secondary porosity derived from dissolution of detrital grains. Framework grains: quartz (Qtz), feldspar (Fs), volcanic rock fragment (VRF), metamorphic rock fragment (MRF); cement: calcite (Cal), chlorite coat (Chl-c); primary porosity (PP) and secondary porosity (SP).

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