Cenozoic Inversion Structure of Liaozhong Depression and Its Control to Later Oil-gas Accumulation

Various styles of inversion structures are developed in Liaozhong depression along Tan-Lu fault zone, which are directly related to the Cenozoic tectonic activity of Tan-Lu fault zone of Liaodong bay segment. This paper... [ view full abstract ]

Various styles of inversion structures are developed in Liaozhong depression along Tan-Lu fault zone, which are directly related to the Cenozoic tectonic activity of Tan-Lu fault zone of Liaodong bay segment. This paper studies the geometry characteristics, evolutionary process and inversion phases of inversion structures in Liaozhong depression by utilizing the latest seismic profile, coherency time slice data and balanced profile restore method. The results show that the inversion structures in Liaozhong depression mainly consist of inversion fault, inversion anticline and buried uplift.. Liaozhong depression has experienced three stages of tectonic inversions which occurred at the end of Sha-3 member, Dongying formation and Minghuazhen formation respectively. All the three stages of tectonic inversion are closely related to the Cenozoic activity of Tan-Lu fault zone, which are fundamentally controlled by the change of surrounding plate motion: the first stage of tectonic inversion is induced by the descent of restraint action to Tan-Lu fault zone, which is caused by the decline of extensional rifting action, and form the rudiment of inversion structure; the second stage of inversion is induced by the aggravation of Tan-Lu fault zone’s compressional strike-slip, which is caused by the sudden increase of plate subduction rate, and form the finalized shape of inversion structures. the third stage of inversion is induced by late revival of Tan-Lu fault, which is caused by accelerated subduction of pacific plate. Among the three stages of tectonic inversion, the first and third tectonic inversions are weak and developed in local area, but the second inversion is violent relatively and developed in the whole region. Influences brought by the inversion structures to hydrocarbon accumulation and distribution in Liaozhong Depression are mainly shown in the following aspects: due to tectonic inversion in first and second phases, hydrocarbon generation and expulsion of Paleogene source rocks were delayed, so that large-scale hydrocarbon generation and expulsion did not occur during Paleogene, only smal-scaled reservoirs were formed and hydrocarbon is usually low-mature. The tectonic inversion in the third phase matched with the principal generation and expulsion period of source rock, causing destroy of Paleogene reservoirs and hydrocarbon diffuse into shallow layers. The Neogene reservoir in Liaozhong depression is featured by “rapid charging and accumulation in later period”, wherein low-mature oil and high-mature oil coexist, and ther quantity and scale far exceed those in Paleogene reservoirs.