A Study On Fuyu Reservoir In Putaohua Oilfield Of Daqing Area

Putaohua oil layer is located in Putaohua structure which is a3rd-order structure in the south ofDaqing Plaeanticline of center concave in Songliao basin. It borders Taipingtun anticline to thenorth and Aonan nose structure to the south. Sanzhao sag and Gulong sag are on the east and westof it. The upper part of3rd Member and4th Member of Quantou Formation are the target strata,which are stably distributed with a thickness of240-290m.Based on the theory of high resolution sequence stratigraphy and related seismic data, the changesin base level cycle of Fuyu reservoir are analyzed in term of short term, mid-term and long termcycles. Through the identification of the cycle surface, the reservoir is carefully classified andcompared. Fuyu reservoir within the studied area is divided into three sand groups F1, F2, F3. F1sand group is further divided into three minilayers F11, F12, F13. F2sand group is further dividedinto two minilayers F21, F22. F3sand group is further divided into two minilayers F31, F32.According to the superposition study of short term cycles, the reservoir is divided into twomid-term cycles. F1sand group is a separated mid-term cycle, while F2and F3sand groups formthe other mid-term cycle. The combination pattern of mid-term cycles demonstrates thatretrogradation combination is the major part of Fuyu reservoir which is a rising half cycle of athird order cycle. All these show that the sedimentary period base-level of Fuyu reservoir is risingin general.Fuyu reservoir within the studied area is mainly shallow-water delta sedimentation. Based on theanalysis of lithology, logging information and related seismic data, the microfacies models are setup which shows that this area is mainly composed by two subfacies delta plain and delta front.Delta plain subfacies include5kinds of microfacies: distributary channel, interchannel, naturallevee, crevasse spray, and flood plain. Delta front subfacies include4kinds of microfacies: underwater distributary channel, underwater interchannel, underwater natural levee and sheet sand.From F3to F1, the lake strandline of the studied area moved from southwest corner to thesoutheast corner and until F11, the area was fully covered by the lake. The move of the lakestrandline directly influenced the development of sedimentary microfacies, so the delta plainsubfacies slowly shrinked and the area of delta front subfacies gradually increased from F3to F1period. In F11period, only delta front subfacies were included in the studied area.Because of sedimentary environment, Fuyu reservoir in the studied area is characterized with thinsand body, drastic lateral variation, scattered distribution and great heterogeneity. To deal with thisproblem, seismic inversion is conducted in this thesis with the guidance of well loggingconstrained inversion technology. Through this inversion, the distributing characteristic of sandbody in this area can be predicted. According to the results, sand body is scattered distributedwith small thickness and width. From F3to F1, the number of high value centers increases and thehigh value areas are distributed in belt shape in the north and south trend. And the numbers of highvalue areas go up with the trend. All these show that the development of sandstone is gettingbetter.The relation between inversion velocity and reservoir quality can be established through whichreservoir physical property can be predicted from points to the area as a whole. The linear relationbetween inversion velocity and porosity can also be predicted is the research, so the porosity in thework area can be predicted. The research result shows that from F3to F1sand group the porosityvalue gradually increases which indicates the development of porosity becomes better and better.The value varies from5%to15%. Then, by confirming the exponential relation between porosityand permeability, the permeability in the studied area can also be forecasted. The result shows thatthe predictive permeability value and infiltration capacity in the work area are comparatively low.However, from F3to F1sand group permeability value is on the rise which demonstrates that thepermeability is getting better. The value varies from0.1mD to1.6mD which belongs to superlow-low level. Thus, Fuyu reservoir in the studied area is the combination of low porosity-lowpermeability reservoir and super low porosity-low permeability reservoir.According to the "Grey theory" principle, porosity, permeability, velocity, sand rate and the thickness of sand are selected as parameters to evaluate Fuyu reservoir. The reservoir is dividedinto four grades, from Grade1to Grade4, the quality of the reservoir becomes worse and worse.The reservoirs of Grade2and Grade3are most widely distributed, followed by those of Grade1and Grade4in order. The reservoirs of Grade1and Grade2are the most potential, which arebanded distributed.