Abstract:

On the basis of comprehensive analysis of drilling, logging and core data, it is considered that carbonate reservoir of grain shoal is an important reservoir type in Leikoupo Formation, Middle Triassic, southwest Sichuan Basin. The reservoir types of two different patterns of porosity and permeability have been mainly developed:(1) Dolarenite reservoirs are dominated by residual intergranular pores and intergranular dissolved pores in the reservoir space, and are possessed of well developed throats with neck down and shaped tube, and are characterized by the good reservoir capability with medium porosity and permeability;(2) Oolitic limestone and residual bioclastic dolomite reservoirs are dominated by isolated intragranular dissolved, moldic and organisms pores in the reservoir space, and are possessed of less developed throats which mainly are miniature in the dimension, and manifest as medium porosity and low permeability. Analysis to the controlling factors of these reservoirs suggests as follows: (1)Grain shoals lay the foundation to the reservoir; (2)Reservoir pattern is controlled by the thickness of a single shoal; (3)The preservation of primary intergranular pores is the key to dolarenite reservoirs, while syndiagenetic meteoric leaching is crucial to reservoirs of oolitic limestones and residual bioclastic dolomites.

Key words: grain shoal, reservoir characteristics, controlling factor, Leikoupo Formation, southwest Sichuan Basin