Fracture, Dissolution, and Cementation Events in Ordovician Carbonate Reservoirs, Tarim Basin, NW China

Figure 7

(a) Hand specimen of the Lianglitage Formation showing F5 fractures cemented by fluorite and calcite (Cc5). Silica mineralization in the host rock along the fracture wall. (b) Plane light optical photomicrograph showing fluorite, barite, and Cc5a calcite cement precipitated within a F5 fracture. (c) Plane light optical photomicrograph showing recrystallization of host rock by calcite and celestite mineralization. Note pores (filled with blue epoxy) formed around the celestite crystals. (d) Plane-light optical photomicrograph showing partial replacement of the host rock by silica mineralization. Note pores associated with silica replacement. (e) Hand specimen of Yijianfang Formation showing F6 fractures. (f) Plane light optical photomicrograph showing F6 fractures filled with Cc6 cement postdating Cc4-bearing F4 fractures. (g) Hand specimen of the Yijianfang Formation showing irregular, multidirectional S2 stylolites that give the rock a pseudonodular appearance (stylobreccia). Note that S2 is associated with F7 fractures and V7 vugs. (h) Plane light optical photomicrograph showing stylobreccias and their association with F7 fractures. Dolomite cement (Dc1) precipitated along S2 stylolites. F7a fractures filled with calcite cement (Cc7a). (i) Plane light optical photomicrograph showing F7b fractures and S2 tectonic stylolites containing blocky calcite (Cc7b) and dolomite cement (Dc1). Notice that pores around Dc1 crystals are filled with bitumen. (j) Plane light optical photomicrograph showing bedding-oblique stylolitic and sheared F7c fractures containing insoluble material, bitumen, and calcite cement (Cc7b). (k) Plane light optical photomicrograph showing an F7a fracture filled with calcite cement (Cc7a) forming synkinematic bridges and V7 vugs filled with blocky cement (Cc7b).

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