Abstract:

The deep-burial carbonate rocks in China are characterized by great burial depth, old numerical age, and complex geological evolution process. The formation and distribution of carbonate reservoirs, constrained by many factors, are one of the key scientific issues in marine oil and gas exploration. This paper summarizes the results of the team’s long-term research and reveals the main development conditions and orderly distribution of multi-type carbonate reservoirs relevant to the formation and modification of deep-burial carbonate rocks in the Tarim Basin. (1) The platform pattern, stratigraphic development and evolution, and late-stage burial and modification of the basin are all the tectono-sedimentary responses of the basin margin tectonic events. The early Paleozoic basin experienced the evolution process of geomorphic extensional differentiation and formation of small rift groups, geomorphic compression differentiation and interlayer unconformity development, paleo-uplift and large-scale unconformity, multi-stage unconformity superposition and buried modification of paleo-uplift. (2) Complex sedimentary differentiation and evolution (in terms of type and scale) during carbonate platform sedimentation can be divided into embryonic stage, construction stage, heyday stage and decomposition-extinction stage. The corresponding platform margins have undergone the construction process of gentle slope, progradation rimmed, aggradation rimmed and retrogradation steep slope. They control the distribution of sedimentary facies zones favorable for large-scale reservoir development, such as platform margin reef shoals, intraplatform shoals and early dolomitization tidal flats. (3) Multi-level unconformity and fault-fluid modification are important mechanisms for the formation of high-quality reservoirs, where multi-stage regional tectonic activities and periodic sea-level changes control the development of unconformities at different levels, while sequence boundaries dominated by sea-level fall leads to periodic outcropping of carbonate rocks to form interlayer karst and synsedimentary karst of different scales; meanwhile large-scale unconformities formed by regional tectonic movements control the large-scale carbonate outcropping and development of large-scale epigenetic karst reservoirs, as faults and fractures of different scales are not only the reservoir development zones but also the main zones of fluid activity and modification. (4) The size of unconformity and the intensity of fault activity in the Tabei-Shunbei area change gradually from north to south controlling the orderly change of reservoir type and distribution, which result in the sequential developments of, from north to south, buried hill dolomite reservoirs in the Yakla fault convex, paleo-weathered crust karst reservoirs in the main area of Tahe area, stratabound karst reservoirs in the slope area of Tahe, fault karst reservoirs in the covering area of Tahe area, and fault-controlled karst reservoirs in the Shunbei area, reflecting the gradual weakening of unconformity control on reservoirs and strengthening of fault control on reservoirs from denudation area to covering area.

Key words: deep-burial carbonate rocks, formation and modification process, orderly distribution of reservoirs, Tarim Basin