Characteristics and Geological Origin of High Flow Zones in Thick Bioclastic Limestone

Abstract

Summary The universal character of High Flow Zones (HFZs) in thick bioclastic limestone is unclear. The origin of HFZs is diverse, and the origin of HFZs in thick bioclastic limestone need further studied. Based on core, cast thin sections, physical property, mercury intrusion and nuclear magnetic resonance and Production logging tests (PLT) data. The depositional model of the study area is first determined, the depositional environment of the formation of the HFZs is analysed, and the diagenesis of the HFZs is also recognized. Secondly, the common characteristics of the HFZs, including lithology, physical property, pore type, throat size, log curve and development performance, are analysed comprehensively. Finally, the origin model of HFZs in thick bioclastic limestone is established. The HFZs are mainly formed in the tidal channel and barrier shoals. The reservoir space contains primary pores and secondary pores, which is the result of the coupling of high energy environment and constructive diagenesis. The high energy depositional environment has clean particles with good primary physical properties of rocks. and the dissolution during the time of sea level decline is the key factors for the formation of HFZs. As a result, a large number of secondary pores are formed, the size of pore throat is enlarged, and the porosity and permeability are greatly increased. On the whole, the physical properties of rock are coupling controlled by sedimentation and diagenesis.