The Affection Of Diagenesis On Fault Sealing Of Kexia Fracture Belt In Junggar Basin

Most of the explored hydrocarbon reservoirs of Kexia Fracture Belt in Jungger Basin are related with fault. As explorative developing, finding potential reserve volume becomes more and more important. Fault sealing is the significant factor which affected distribution of hydrocarbon reservoirs. Study on the affection of diagenesis on fault sealing, especially the affection of cementation is a new theme. Therefore, further studies should be carried on, which is significant for the formation and occurrence of fault block hydrocarbon reservoirsBy means of analysis on fault block hydrocarbon reservoirs of Kexia Fracture Belt, this dissertation defined master control faults which dominate distribution of hydrocarbon reservoirs. Based on feature of fault, history of sealing and well logging, studied the affection of compaction and packing action on fault sealing with quantitative assessment and ambiguous evaluation. Based on rock core and outcrop, studied the affection of cementation and denudation on fault sealing with core wafer, scanning electron microscope and fluid inclusion. Then prospects of fault block hydrocarbon reservoirs were predicted. Influenced range and stage of diagenesis were analysed at last.The study on formation of fault block hydrocarbon reservoirs showed that fault- unconformity compound conduction was base, updip seal of fault was key, lithology and sedimentary facies in downdip direction and lateral layer were necessary conditions. Moreover, control faults, which include 5 primary faults that are Kelamayi, Nanbaijiantan, Baikouquan, Baiwu and Xiahongbei Faults, and 5 secondary faults that are 426 Fault, wu29 Fault, Liqingcun Fault, Xia10 Fault and Xia21 Fault, were defined. These faults displayed straight mode, S mode and wave mode in plane; were divided to two rift systems which include deep rift system and shallow rift system in section. History of fault sealing demonstrates that buried depth was low, but because of strong tectonic stress, fault sealing was good for hydrocarbon reservoir in Kexia Fracture Belt after the stage of Jurassic Sangonghe group. In that time fault sealing of Nanbaijiantan Fault was best, secondly include Baikouquan Fault and Xiahongbei Fault, they could seal hydrocarbon and create fault block hydrocarbon reservoirs. Fault sealing of Kelamayi Fault was worse, which could become pathway for migration of hydrocarbon.Faults in Kexia Fracture Belt were formed by strong compression and overthrust. Thus compaction was intense in research area and the affection of compaction was obvious. Compaction in Wuxia area(>40MPa) was stronger than that in Kebai area in plane. Compaction of Baikouquan Fault and Baiwu Fault was strongest, which of Kelamayi Fault was worst. In section, shallow compaction was mainly affected by regional major stress, it become stronger with fault dip angle increase. Deep compaction was affected by buried depth and fault dip angle. Low depth and small angle generated strong compaction and good sealing. Packing action of fault in Kexia Fracture Belt was ordinary. Few Rm value exceed 0.6. Generally, Packing action of faults in Wuxia area(Rm>0.3)was better than that in Kebai area(Rm<0.3).This feature of Packing action was affected and controlled by regional lithologic character.Cementation was intense in Kexia Fracture Belt, which made porosity and permeability decreased, fault sealing became better. The mineral sequence of cementation was chlorite & zeolite- calcite- kaolinite- illite- ferrocarbonatite. Affect by formation water and history of fault development. From south to north, Kelamayi Fault-Nanbaijiantan Fault and 426 Fault-Baikouquan Fault-Xibaiwu Fault-Xiahongbei Fault, mineral of cementation successively was chlorite, zeolite- calcite- calcite, clay mineral- calcite, ferroan calcite- ferrodolomite, siderite. Those indicated the sequence of cementation from south to north incline to late period. Occurrence of feldspar corrosion was common and dissolution of carbonate cement was few. Denudation was not evident in Kexia Fracture Belt, the affection of denudation on fault sealing was faintish.Based on the research that affection of diagenesis on Fault Sealing in Kexia Fracture Belt, favourable regions of reservoirs were predicted: Jurassic formation in foot wall of Kelamayi Fault and Baikouquan Fault; hanging wall of Xiahongbei Fault.The affection coverage of cementation was wide. The coverage of primary faults was about 60-120m, that of secondary faults was about 40-50m. Analysis of inclusion in calcite showed that there are 3 stages of geofluid in Kexia Fracture Belt. Saline inclusion had 2 stages, correspondent homogenization temperature was 40~70℃,70~110℃. Hydrocarbon inclusion had 3 stages, correspondent homogenization temperature was 40~70℃,70~110℃and 100~130℃. So the time of geofluid migration could be ascertain that the first stage of geofluid migration was early Triassic period (B.P.230~240Ma), the second stage was late Triassic period to early Jurassic period(B.P.200~220Ma), the third stage was late Jurassic period to Cretaceous period(B.P.125~150Ma). Calcite in fault was formatted in the first and second stage of geofluid migration.