Application of new dating and temperature-measuring technologies in study of strike-slip fault-controlled reservoirs and hydrocarbon accumulation: A case study of Ordovician strata in non-foreland area of Tarim Basin, NW China

Focusing on the geochronological issues related to the matching relationship between the strike-slip fault activity and the stages of hydrocarbon generation, reservoir formation, and hydrocarbon accumulation, this study aims to quantitatively constrain the tectonic–burial history, hydrocarbon generation history, reservoir porosity evolution history, and hydrocarbon accumulation history by determining the isotopic ages and temperatures of multiphase calcites (particularly the calcites which contain hydrocarbon-bearing fluid inclusions) and quartzs filling the fractures in the Ordovician strata within the non-foreland area of Tarim Basin. Three major findings have been obtained. (1) According to the tectonic–burial history restored under the constraint of the isotopic ages and temperatures, the non-foreland area of the Tarim Basin experienced a continuous burial process during the Cambrian–Ordovician period, with only a minor uplift at the end of the Silurian. Overall, the area was characterized by continuous hydrocarbon generation and a gradual increase in vitrinite reflectance (Ro). (2) While mechanical compaction and pressure-solution during burial progressively reduced the matrix porosity, the strike-slip fault activity during the Middle Caledonian II and III episodes induced physical fragmentation, which created extensive interbreccia pores, fault cavities, and structural fractures as seepage pathways for surface runoff, and, in conjunction with interlayer karstification, led to the development of widespread dissolution vugs. The formation of fracture-vug system in the Ordovician limestone provided effective storage space for hydrocarbons generated during the Late Caledonian and subsequent periods. (3) The Ordovician fault–karst limestone reservoirs underwent four stages of hydrocarbon accumulation: low–medium maturity liquid hydrocarbons during the Middle–Late Caledonian, medium–high maturity liquid hydrocarbons during the Middle–Late Hercynian, high maturity liquid hydrocarbons during the Indosinian, and high–over maturity gas during the Middle Yanshanian. Variations in hydrocarbon accumulation among different strike-slip faults or different segments of the same fault are controlled by differences in source rock maturity across structural units, as well as by the timing of fault activity and fault-related connectivity to hydrocarbon sources. This research also establishes a geochronological framework for investigating strike-slip fault- controlled reservoir formation and hydrocarbon accumulation, facilitating a more accurate determination of the reservoir formation and hydrocarbon accumulation stages, and providing critical insights for evaluating hydrocarbon enrichment zones in fault-controlled reservoirs.