Effect of Multi-Stage Strike Slip Faults and Fluids Effect on the Origin and Evolution of a Deep Carbonate Reservoir in the Southern of Tahe Oilfield, Tarim Basin

In Tarim Basin, China, carbonate strata at great burial depths contain abundant petroleum. There has been no notable weathering of the Middle and Lower Ordovician limestone in the southern area of Tahe Oilfield due to the shielding effect of the Upper Ordovician strata; however, the origin and evolution of these carbonate reservoirs is controversial. Based on cores, well logging, image logging, and new 3D seismic data analysis, these reservoirs in the study area were divided into three types: dissolved pores, fractures, and caves. The characteristics and formation of Paleozoic faults in the southern Tahe oilfield have been studied. The results indicate that four stages of fault systems developed: extensional faults in the Cambrian-Early Ordovician, strike-slip faults in the Middle Ordovician, and reactivation of strike-slip faults in the Silurian-Devonian, and faults related to volcanic activities in the Permian. Cathodoluminescence, geochemical parameters, and fluid inclusions are used to investigate fault-controlled fluid compositions. There are four main types of diagenetic fluids (meteoric water, formation water, hydrothermal fluid, and mixed fluids) and their diagenesis evolution is discussed. The coupling relationship between diagenetic fluids and strike slip faults controls the development of reservoirs. During the karstification process, mixed dissolution of meteoric water and hydrothermal fluids contributed greatly to the development of these carbonate reservoirs, with multi-stage inherited faults controlling the fracturing of cave reservoirs. Two stages of NNW and NNE trending “X” conjugate strike-slip fault systems formed in the Middle Caledonian and Early Hercynian was important for diagenetic fluids migration and dissolution. The faults formed during the Late Hercynian are the main area of hydrothermal fluid migration, resulting in both hydrothermal dissolution pores and cave formation. This work shows that it can provide theoretical guidance for deep oil and gas exploration and development.