229 / 2019-06-28 15:29:13

Genetic types and characteristics of carbonate shoal reservoirs: A case study of the Middle Triassic Leikoupo Formation in Sichuan Basin, SW China

genetic types; reservoir; carbonate shoal; Leikoupo Formation; Sichuan Basin

The carbonate shoal reservoirs of the Middle Triassic Leikoupo Formation in Sichuan Basin are important gas-producing strata. The Genetic types and characteristics of carbonate shoal reservoirs were studied by using the data of drilling, logging and core in the Middle Triassic Leikoupo formation. The results show that The carbonate shoal reservoirs can be divided by their genetic mechanism into residual intergranular pore type reservoirs, karstification type reservoirs (further divided into syndepositional karstification type reservoirs, burial karstification type reservoirs and supergene karstification type reservoirs), dolomitization type reservoirs, and composite type reservoirs. Residual intergranular pores and dissolved pores are the main reservoir spaces in the residual intergranular pore type reservoirs, and Pore throats are mainly tubular or constricted, with good connectivity. This reservoir is characterized by high porosity and high permeability. Isolated intragranular corroded pores and moldic pores are the main reservoir spaces in syndepositional karstification type, and Pore throats are less developed with poor connectivity. This reservoir is characterized by high porosity and low permeability. The reservoir space types of burial karstification type reservoirs are mainly the dissolution pores formed by non-fabric-selective dissolution and intragranular solution pores and intergranular solution pores formed by fabric-selective dissolution. The difference scales and forms of pores and holes are main reservoir space of supergene karstification type reservoirs, which are mainly caused by the significant sea level drops or tectonic movement. Intercrystal pores and intercrystal solution pores are the main reservoir spaces of dolomitization type, and Pore throats are good in connectivity. This reservoir is characterized by high porosity and high permeability. Composite type reservoirs are characterized by a variety of reservoir spaces with pores, holes, and fissures. The further research discovers that The northwestern Sichuan Basin mainly developed residual intergranular pore type, residual intergranular pores + burial karstification type and residual intergranular pores + burial karstification + dolomitization type，The central, eastern and northern Sichuan Basin mainly developed syndepositional karstification type and syndepositional karstification + dolomitization type，Epigenetic karstification widely distributed in the 70 m to 90 m thick stratum under the plane of unconformity between the Lei-4 member and the Xu-1 member in Sichuan Basin.