Grading evaluation and prediction of fracture-cavity reservoirs in Cambrian Longwangmiao Formation of Moxi area, Sichuan Basin, SW China

WANG Bei,LIU Xiangjun,SIMA Liqiang

Table 6 Grading evaluation criteria and prediction of reservoirs in Longwangmiao Formation of Moxi area.

Reservoir grade Reservoir type Grading evaluation criterion Main controlling factor Geophysical response characteristics Dynamic response characteristics Comprehensive evaluation Physical parameters Pore throat parameters Development degree of dissolved vug Tectonic location Sedimentary environment Diagenesis Logging response Seismic response Testing characteristic Productivity characteristic Production testing characteristics Grade I fracture- cavity reservoir Fracture-cavity reservoir is the main reservoir, with a few fracture-pore reservoir Porosity > 7%, Permeability is 5×10-3 μm2, Median hole throat radius ≥ 0.7 μm, Surface porosity > 6% The high part of structure in Longwangmiao Formation top Dominated by the main body of grain beach Influenced by contemporaneous to penecon- temporaneous dissolution, burial disso- lution and supergene dis- solution, the effect of super- gene disso- lution on the reservoir of Longwangmiao Formation is most obvious With Δt of 138.0-156.2 μs/m, Density of generally less than 2.8 g/cm3; ?CNL of 5%-10%; LLD of less than 4000 ??m; FMI imaging feature is patchy mode Strong crest type Average testing yield is greater than 100×104 m3/d Average open flow capacity is greater than 400×104 m3/d Tubing pressure is stable; Average daily gas production is greater than 100×104 m3/d High-yield type Grade II fracture- pore reservoir Fracture-intergranular pore reservoir is the main reservoir, with a few fracture-cavity reservoir With a porosity of 4%-7%, Permeability of (0.5-5.0)× 10-3 μm2, Median hole throat radius of 0.2-0.7 μm, and surface porosity of 3%-6% The structural high or slope of Longwangmiao Formation structure Margin of grain beach and diamictic tidal flat With Δt of 135.1-150.1 μs/m; Density of 2.7-2.85 g/cm3; ?CNL of 4%-8%; LLD of less than 5000 ??m; Featuring block mode on FMI image Weak crest type Average testing yield is (30-100)×104 m3/d Average open flow capacity is (50-400)× 104 m3/d Tubing pressure is stable; Average daily gas production is (30-100)×104 m3/d Medium-yield type Grade III intercry- stalline pore reservoir Intercrystalline pore reservoir is the main reservoir, with a few fracture-intergranular pore reservpor With porosity of 2%-4%, Permeability of (0.05-0.50)× 10-3 μm2, Median pore throat radius of 0.02-0.20 μm, and surface porosity of 3%-5% The lower part of structure in Longwangmiao Formation top Lagoon and interbeach sea With Δt of 132.1-144.1 μs/m; Density of 2.75-2.85 g/cm3; ?CNL of 3%-6%; LLD of less than 5000 ??m; FMI imaging is characterized by low conductivity anomalies of basically the same color Wave trough type Average testing yield is less than 30×104 m3/d Average open flow capacity is less than 50×104 m3/d Low-yield type