High Resolution Sequence Stratigraphy And Reservior Characteristics Of Triassia YanChang Formation In ZiBei Oil Field

The high resolution sequence stratigraphy having been extensively applied to oilexploration and development studies in continental oil-bearing basin and got hot throry.Dueto its bran-new theory,concepts and methods effective decide the concealed oil exploration,reservoirs careful correlation and characteristics research.In order to meet the needs ofreservoir heterogeneity characteristic at medium-late development strage,the paper for thefirst time applies the theory to reservoir characteristics of YanChang Formation in ZiBeioilfield and transver the theory and method to the whole reservoir research.Moreovercombined with the sedimentary,reservoir geology and petroleum geology systematicallystudied the sedimentary facies,the sequence stratigraphy,the distribution of sandbody,thereservoir characteristics and heterogeneity.For the first time,the Chang6-Changl oil-bearing beds of YanChang Formation aredivided into 3 long term,15 middle term and 28 short term base-level cycle sequences inwhich 3 types and 7 subtypes short term base-level cycle sequences are identified.Accuratehigh-resolution equitime correlation is made and sequence framework is established.Thedistribution laws of sandbody are studied in the sequence framework.The study shows thatthe high-resolution sequence stratigraphy can be applied quite well to continental oil-bearingbasin and not only meets the needs of the oilfield's exploration and development but also is ofimportant theoretic value.Systematic reservoir study of Chang6-Changl oil-bearing beds of YanChang formationindicates that the main genetic reservoir sandstones are the delta front submerged distributarychannel sands,the channel barrier,the delta plain distributary channel and the braided streamchannel sands.The reservoirs weathered the diagenesis such as the compaction,thecementation and the dissolution.The mechanical compaction and the chemical pressuresolution at the early diagenesis maked the pore small.The cementation at early of the latediagenesis maked the pore small by filling.The dissolution at late of the late diagenesismaked the pore large.These are the main diagenesis-pore evolution strage.The main pore arethe remnant intergranular pores,intergranular solution pores,intragranular solution pores andintercrystal pores,of them the remnant intergranular pores being dominant.The crack doesn't develop.The main throat is fine throat.The connection of pore-throat is poor.Theentry pressure and median pressure are more higher.The structure of pore is more poor.Thereservoirs are low porosity and low permeability.The physical property of Chang2 is the best.The sedimentation and digenesis controlled the reservoir.The medium-fine-grainedsandstones form good reservoirs,the fine-grained sandstones form medium reservoirs and thesiltstones form poor reservoir;Sandbodies mostly developed in stream channel and deltadistributary channel microfacies.They decided the development,distribution and physicalproperty of reservoir rock.The physical property of stream channel is good and thedistributary channel,the channel barrier are secondary;The dissolution developed at the latediagenesis improved the reservoirs property.The analysis of reservoir heterogeneity suggests that the interlayer heterogeneity of theChang2~3(MSC9),Chang2~2(MSC10),Chang2~1(MSCll)are more isotropic,Chang6~3(MSC2),Chang6~2(MSC3),Chang6~1(MSC4)and Chang 4+5(MSC5+MSC6+MSC7)are more serious.The differentia of porosity between each bed is obvious and thedifferentia of permeability between each bed is more obvious.The analysis of relationship between high-resolution sequence stratigraphy and thereservoir development and heterogeneity shows that in the sequence framework the reservoirsandstones mainly locate near the boundaries of the middle term base-level cycles,amongthem the braided stream channel sandstones,delta distributary channel sandstones distributein the lower to middle parts of the middle term base-level rise cycles and channel barriersandstones distribute in the middle to upper parts of the middle term base-level down cycle.Five heterogeneity models of different microfacies are founded:Pooring-upward pattern ofphysical;Gooding-upward pattern of physical property;Homogeneous pattern of physical;Pooring-upward and gooding-upward pattern of physical property;Complex pattern ofphysical property.They are closely relative to the changings of the high resolution sequencestratigraphy base-level cycles.