Hydrocarbon Migration-Accumulation Model In The Deep Carbonate Rocks, Tahe Oilfield

This thesis involves systematical studies on petroleum geologic conditions, conduit systems, petroleum migration events and directions, energy fields (tectonic stress field, temperature field, pressure field and fluid chemical field) in the deep carbonate rocks. The laws of petroleum migration in the deep carbonate rocks in this region are discussed, and the hydrocarbon migration-accumulation model for this region are finally established.According to the studies, Tahe Oilfield has oil sources from outside on the whole. The sources are mainly from Cambrian - Lower Ordovician source rocks in the Manjiaer Depression. The deep carbonate rocks of Tahe Oilfield develop three conduit systems - fracture system, unconformity system and karst network system. There are four hydrocarbon migration predominant pathways with multistage petroleum charging events in the main oilfield, two from south to north and the other two from east to west.Through the systematical studies on energy fields in the deep carbonate rocks, it has an obvious particularity. There are mainly five tectonic stress activities in the Tahe area, which is under the low tectonic stress region nowadays. Temperature field here is characterized by low geothermal gradient. The activities of fluid in low temperature regions are relatively intense, and it is more advantageous in low geothermal regions for hydrocarbon migration and accumulation. The formation pressure in Tahe Oilfield fluctuate around the normal pressure without big deviation, but the abnormal high or low pressures distribute disorderly for the influences from fracture forming activities. The deep formation water in Tahe Oilfield is CaCl2-typed formation water with high TDS, and the analyses on inclusions demonstrate that there were 4～5 stages of formation water activities.Systematical studies indicate that energy fields have substantial connections with hydrocarbon migration and accumulation. Tectonic stress is not only the main controlling factors for the formation and reconstruction of regional faults, but also the driving force of long distance petroleum migration. Temperature field can indicate hydrocarbon migration and accumulation, and it is more advantageous in low geothermal regions for hydrocarbon accumulation. Abnormal pressure distributing disorderly is the main driving force for short distance hydrocarbon migration and accumulation. The compartmentalization of formation pressure promotes the inhomogeneity of fracture forming and dissolution in carbonate reservoirs, which breaks the consistency of reservoir development. Fluid chemical field indicates that the whole preservation condition is good. However, multi-stage changes of palaeosalinity have led to the inhomogeneous forming of karst formation.Combined with the characteristics of petroleum accumulation in Tahe Oilfield, The model for hydrocarbon migration-accumulation in deep carbonate rocks is established. Hydrocarbons generated from the Cambrian-Lower Ordovician in Manjiaer Depression migrate southward under the driving forces of tectonic stress along the unconformable surface with a long lateral distance. After reaching the Tahe area, the hydrocarbons accumulate in the main oil-bearing region through two pathways that are respectively from south to north and from east to west. The reservoirs with enriched weathering fractures and karst caves are considered to be preferred hydrocarbon accumulating area. Then hydrocarbons move longitudinally along the faults to subclass reservoir such as fractures and karst cave, and finally, enter the karst holes, cavities and fissures which are the minimal accumulating cells under the driving forces of abnormal pressures. In all of the influence factors, the conduit system is the most important one.