Characteristics Of The Chang3Member Reservoir Of Yanchang Formation In The Easten Zhiluo Oilfield, Ordos Basin

Research area in the east of zhiluo oil field, which exploration area amount to450km2and is located in the southeast of Ordos basin and Northern Shanxi monocline.Chang3member is the major oil producing zone,however the test oil results anti ideal and low productivity. Comprehensive applied with sequence stratigraphy, sedimentary petrology, geochemistry and other theories and methodologies. Applied with geological outcrop, well boring, logging, production dynamic data, scanning electron microscope, thin section identification and analysis means of physical property system study the source direction, reservoir petrologic character, microscopic reservoir pore structure characteristics, diagenesis, law of spread of sand body and sedimentary parfacies. On the basis of reservoir characteristics and controlling factors of Chang3member, we can prediction the favorable target area.Under constraint of the key horizon of research area, more than60wells’ stratigraphic of Yanchang group was fine classed and correlated by the antitheses of thickness cycle. Obtain a very good effect about top structural map, sand body spreading, water-oil relations and whole area closure. The sources direction is the NNE.The same as the direction of the river channel. Study sedimentary features of delta plain.Describe the character of sediment microfacies about distributary channel and interdistributary in detail.This page to analysis the spatial distribution of sedimentary facies.Sandstone body of Chang32member is developing very well and a main oil reservoir. Sandstone body of Chang31and33members are poor.Sedimentary cycle of Chang31-3is apparent.Sandstione classification of Chang3memeber is feldspar-lithic fine-sandstone and feldspar fine-sandstone.The content of cement is high which salient feature is laumontite cementation. Remnant intergranular porosity and intergranular dissolution porosity are main reserving space.Collection type of porosity consist of remnant intergranular porosity, intergranular porosity-micropore, dissolution porosity-micropore, micropore, mixed. The anisotropism is medium to strong.The factors of reservoir with low permeability and low porosity can be illuminate as following:①Low compositional maturity, textural maturity and particle diameter causes its original porosity low;②High plastic component which include detritus causes strong early mechanical compaction with most original voids volume disappear.③The cementation of calcite and ferrocalcite in later period of diagenesis is another primary reason. Four kinds of diagenetic facies appear in this area:biotite compaction facies, chlorite cementation-feldspar corrode facies, chlorite cementation-laumontite-corrode facies,carbonate cemenation facies.Critical factor of oil/gas accumulation are the matching about effectively sand bodies and nose-like uplifts and good hiding condition in Chang3memeber.On the migration of oil and gas side, reservoir forming is transverse migration.From reservoir evaluation study, Chang3member can be divide3kinds of payable area, which has two class I targets,two class Ⅱ targets and one class Ⅲ target.