Study On Natural Gas Transporting And Preservation Conditions Of Huoshiling Formation In Dehui Fault Sag,songliao Basin

In recent years,Huoshiling Formation is the key horizon for deep gas exploration in Dehui fault Sag.Based on geological,logging,drilling and seismic data,the characteristics and preservation conditions of gas reservoirs in Huoshiling Formation of Upper Jurassic in Dehui Fault Sag are studied in this thesis.Through the dissection of typical gas reservoirs,it is clear that the key transporting factors of Huoshiling Formation are faults and unconformities.There are many faults cutting through the Huoshiling Formation in the study area,most of which are high dip normal faults.The faults are generally poorly sealed and oil and gas have predominant migration directions along the fault planes(such as F3 and F5).Faults are good paths for vertical migration of natural gas.Huajia and Nongnan sags are areas with high value of fault conductivity.The "three-layer structure" of unconformities is well developed in the study area at the top of Huoshiling Formation other than Longwang and Helong subsags.Unconformities system are the main pathways for lateral-long-distance migration of natural gas.The areas with high value of unconformity conductivity are concentrated in Huajia subsag and Nong'an graben.Based on the analysis of macro and micro conditions such as distribution characteristics,sedimentary environment,displacement pressure and pressure coefficient of caprock,the capping ability of Huoshiling Formation gas reservoir in this area is comprehensively evaluated by grey clustering evaluation method.The results show that Huajia and Baojia troughs have the best caprock quality and the thickness of the caprocks is relatively large.The caprocks also have three micro-sealing mechanisms: capillary sealing,overpressure sealing and hydrocarbon concentration sealing.By calculating the growth index,the active periods of the faults are analyzed.The results show that most of the faults,except for a few faults such as F3 and F23,have no significant effect on the destruction and transformation of the primary gas reservoirs in Huoshiling Formation.According to the researching results of transport system and preservation conditions,the favorable conditions are overlapped and analyzed,and the next favorable exploration targets in this area are predicted.