Characteristics and significance of the burial dissolution of dolomite reservoirs: Taking the Lower Paleozoic in eastern Tarim Basin as an example

Abstract

Abstract Based on the characteristics of core, thin-section, physical properties and carbon, oxygen and strontium isotope, the characteristics of Lower Paleozoic dolomite reservoirs, dissolution features and mechanism in eastern Tarim Basin were studied. Massive dissolution pore-cave dolomite is the main reservoir type in eastern Tarim Basin. The dissolution pores and caves are mainly medium to small with dense distribution. The fillings in dissolution pores and cracks commonly show negative δ 18 O, generally far lower than the surrounding rock; slightly negative δ 13 C, partially positive; slightly high 87 Sr/ 86 Sr. Proportion of CH 4 and CO 2 is high in fluid inclusions and some of them contain high proportion of H 2 S, which demonstrated that the organic matter was at the high evolution stage when the inclusions were captured, suggesting deep burial circumstances. Silicification and high homogeneous temperature also indicate the presence of hydrothermal fluids. Dissolution includes organic acid dissolution and hydrothermal water dissolution. Acid fluid mainly includes organic acid, CO 2 and H 2 S, which were mainly generated in the process of evolution of organic matter, with a little H 2 S from sulfate reduction, a little CO 2 from volcanic activity. As the carrier of acid fluid, hydrothermal fluids overcome kinetic obstruction of dissolution and dissolve the deep dolomite. Major faults and associated faults provide channels for hydrothermal fluids, the acid fluid was further dispersed in dolomites through numerous inter-crystal pores caused by dolomitization and micro-cracks caused by compaction to complete dissolution for dolomite reservoirs.