The dolostone reservoirs from the Middle Permian Qixia Formation in northwestern Sichuan Basin: Characteristics and controlling factors

The dolostone reservoirs in the Middle Permian Qixia Formation are dealt with in the light of petrographic and laboratory analysis of the core samples and outcrop samples collected from northwestern Sichuan Basin. The dolostone reservoirs in the Formation are composed of crystalline dolostones and residual grainy dolostones. The reservoir spaces include intercrystal pores, intercrystal solution openings, intergranular solution openings, solution pores and solution fissures. The development of the dolostone reservoirs are dominantly constrained by sedimentary microfacies, early dolomitization, late dolomitization, dissolution and tectonism. The shoal microfacies is believed to facilitate the formation of the dolostone reservoirs. The early dolomitization may be favourable for the preservation of the dolostone reservoirs. The dissolution and structural fissures may have exerted key influence on the improvement of the reservoir quality. However, the generation of late dolomites may be destructive to the reservoir spaces.