Diagenetic Processes and Reservoir Heterogeneity in Salt-Encased Microbial Carbonate Reservoirs (Late Neoproterozoic, Oman)

Figure 5

Diagenetic products observed in thin sections and on core: (a) G-2H1 (4950.77 m): columnar, isopachous cement around allochems (yellow arrow) and local reservoir bitumen (RB) within the remaining interparticle porosity. The columnar, isopachous cement likely was formed during early marine diagenesis and the remaining interparticle porosity was during further (deep burial) diagenesis occluded with reservoir bitumen (ppl, 100x). (b) G-8H1 (4951.33 m): dolomite cements (Dol) in a fenestral pore (cathodoluminescence, 100x). (c) E-5H1 (4779.73 m): anhydrite nodule (Anh) with compactional drape (yellow arrow) and relic inclusions of dolomite (observed in thin sections). The replacive nodule, formed prior to physical compaction as indicated by the compactional drape. The position of the sample in the vertical profile of the well is indicated in Figure 6 (core slab). (d) E-4H1 (4797.34 m): anhydrite cements (Anh) within moldic porosity outlined by micritic envelopes (xpl, 40x). (e) G-2H1 (4884.33 m): dolomite (Dol, yellow arrow) cement predating halite cements (Hal) is common in reservoir facies with high primary porosity (ppl, 25x). (f) G-8H1 (4984.20 m): calcite cement (Cc) in intercrystalline porosity, postdating replacive dolomite matrix (Dol) and overgrowth of euhedral dolomite cements (upper yellow arrow). Oil inclusions inside (lower yellow arrow) indicate a precipitation of calcite in the deep burial realm during/after oil migration (ppl, 100x). (g) G-3H2 (4941.49 m): reservoir bitumen-lined stylolite with anhydrite- and calcite-filled tension gash (ppl, 40x). (h) G-2H1 (4889.35 m): inclusions of angular reservoir bitumen and reservoir bitumen-impregnated dolomite (yellow arrow) indicate that halite precipitated after solid bitumen generation (ppl, 25x).

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)