Analysis Of Carboniferous-permian Tectonic Control Of Oil And Gas In The Northeast Of Jizhong Depression

The northeast of Jizhong Depression is the main gas-production area of Huabei Oilfield.Based on the structural characteristics and evolution history research,combined with the transport system and the preservation conditions of the study area,the research on Carboniferous-Permian tectonic controls on oil and gas has been conducted.Experienced complicated tectonic evolution history,the Carboniferous-Permian coal strata in the northeast of Jizhong Depression has experienced five stages:the platform-type sedimentary environment high in the west and low in the east during late Paleozoic,two stages tectonic uplift during Mesozoic,the extension and fault-depression in Paleogene,tectonic inversion during late Oligocene,downwarp in Neogene.Thermal evolution process of hydrocarbon source rock is controlled by tectonic evolution.With the tectonic evolution of the basin,the study area experienced two hydrocarbon generation processes.Primary hydrocarbon-generating period was during Late Triassic,low maturity,hydrocarbon generation amount less;then the formation suffered denudation;along with intense subsidence in Paleogene,the secondary hydrocarbon generation began in the end of Paleogene and Neogene.Structrual styles controlled many types of structural traps.In the process of Jizhong depression evolution,the multi period and different properties structure styles include extensional,strike slip and inversion formed,resulting in various structural traps.Structure controls the distribution of traps.Strike slip structure develops in Wen'an slope and Yangcun slope,and trap type is flower anticline traps.Depression slope with two unconformities formed unconformity-lithologic trap.The slope to the Dacheng swell area is affected by extensional tectonic effects,fault development,development of various types of fault block traps and fault lithology traps.Litan sag in early stage after inversion,the Carboniferous-Permian strata folds obviously,anticline and fault-anticline traps development.Tectonic control effects on hydrocarbon migration include fracture system,unconformity and rock fracture providing pathways for hydrocarbon migration.The two unconformity type and distribution at the end of late Mesozoic era and Late Dongying stage have been studied in the northeast of Jizhong depression,and so have the 3 types of transport system combination type and its distribution.Northeast of Wuqing sag,southern Yangcun slope,middle and northern Wen'an slope,mid-east and south of Dacheng swell develop fault-unconformity-sandbody transport system,which are the most conducive to the natural gas migration of Carboniferous-Permian in the northeast of Jizhong depression.Wen'an slope and southern Dacheng swell develop fault-unconformity or fault-sand transport system,is more conducive to the natural gas migration area.Based on the actual data and the geological condition,the Carboniferous-Permian coal formed gas preservation conditions of the study area are evaluated from 6 aspects which are the cap rocks,tectonic uplift and denudation,fracture degree,volcano activities,formation water chemistry and abnormal high formation pressure,and the Carboniferous-Permian coal formed gas the preservation conditions of multi factor comprehensive evaluation index system is established.Southern Wuqing depression,southwest of Litan sag,northern Wen'an slope area and south of western Suqiao area have good gas preservation conditions,including thick caprock,low sand content;formation without uplift and denudation,or part of uplift and denudation;moderate quantity of fault breaking caprock;no or little igneous intrusion;destructive formation water,high mineralization;abnormal high formation pressure.Hexiwu area,northern Wuqing depression,northern Yangcun slope,eastern belt of Wen'an slope and most of the area Dacheng swell have poor gas preservation conditions.