Study On High Resolution Sequence Stratigraphy And Reservoir Forming Rules Of Gaotaizi Reservoir In Daqingzijing Oilfield

Under the guidance of theories of high resolution sequence stratigraphy and reservoir sedimentology,comparison method of “ approximation of standard isochronous surface of main closed section and reference isochronous surface assembly,guidance of comparative mode of fault and sedimentation,combination of logging and seismic data,and closure of progressive partition”was proposed and applied to divide Gaotaizi reservoir of Daqingzijing Oilfield into 2 long-term base-level cycles,21 middle-term base-level cycles and 82 short-term base-level cycles by utilization of detailed core,logging and seismic data in mature exploration area for sequence division of high frequency and based on sediment dynamics analysis of every base-level cycles and identification of different base-level cycles.Large region,unified and fine sequence framework were established to laid a solid stratigraphic foundation for study on reservoir single sand body identification,sedimentary microfacies and reservoir forming.On the basis of framework control of fine isochronous reservoir,material source,sedimentary system and distribution characteristics of sedimentary facies were analyzed,and delta sedimentary system for Gaotaizi reservoir was proposed,in which Member Qing I and Qing II were affected by Baogang source in southwest and Member Qing III was affected by sources of Yutong in the west,Baokang in the southwest and Huaide in the southeast.Delta front subfacies and predelta subfacies mainly developed in Gaotaizi reservoir and types of microfacies include underwater distributary channel,mouth bar,sheet sand and inter-sheet mud.And fine study on sedimentary facies revealed that high-grade sand bodies in multi large-extra large banded and branched channels and mouth bar of fluvial-delta facies provided key conditions for lithological reservoir forming in the region lack of depressions in large-medium scale structural traps and simple slope settings.On detailed study of regional sedimentary setting and characteristics analysis of microfacies in plane phasing and profile phase,sedimentary mode of banded branch mouth bar in Gaotaizi reservoir of Daqingzijing oilfield was established.Types,characteristics and distributions of 3 deltas in Daqingzijing oilfield were revealed: the steepest(1.23‰)western slope was near-source vertical concave braided river delta,the smoothest(0.42‰)was the southwestern far-source cis concave meandering river delta and the relatively smooth south-south-east was far source oblique concave transitional delta.The establishment of 3 delta sedimentary modes and distribution rules of sand bodies laid a solid foundation for diversities of reservoir forming.On the basis of study on isochronous reservoir framework and spatial distribution of interior single sandbody,modern petroleum geological new concepts such as reservoir forming were fully utilized,technologies of comprehensive analysis of regional reservoir forming and analysis of single sandbody reservoir control mode and oiliness prediction of complex blocks were applied,and the discovered reservoir types and distribution characteristics were systematically analyzed to indicate that sand body of banded branched mouth bar and fault-lithologic traps formed by updip/lateral margin fault were the most important key reservoir-controlling trap types(accounting for over 80%).On the basis of study on geologic conditions and dynamics mechanism of reservoir forming,2 reservoir forming modes in the study area were established: source rock-fault-sand body matching reservoir forming mode and rock-sand body matching closed or semi-closed reservoir forming mode.In accordance with analysis of regional reservoir forming and single sand body,reservoir controlling modes of “ paleo-nosing structure controlling pay zones,oil-source fault controlling trap locations and fault-lithological reservoir controlling trap types” were proposed: favorable pay zones were overlapping regions of paleo-structural zones(structural backbone),faulted zones and banded branched mouth bar zones(dominant sandstone),and lithological updip pinch out zones.Under the guidance of regional reservoir forming modes,7 favorable pay zones were predicted.And under the guidance of controlling factors of reservoir forming of single sand body,172 favorable traps were predicted and 14 wells were deployed.