Reservoir Characteristics And Evaluation Of Yingcheng Formation In Siwujiazi Oilfield Of Songliao Basin, China

Shiwu fault depression lies in the southeast uplift region of Songliao Basin.Songliao basin underwent an early rift stage and a late sag stage.Located inGongzhuling city,Jilin province,Siwujiazi oilfield of Shiwu faulted depression istectonically located in the South Margin of Yangdachengzi anticline belt in theSoutheast uplift of Songliao Basin.Drilling exploration in this oil field started in1989,then the development started in1993.For now the oil-bearing beds of Quantouand Denglouku Formation have been highly explorated and developed relatively,looking for replacement regions will be imperative,thus turning to deep exploration isvery necessary.In view of a low degree of exploration and development in Yingchengand Shahezi Formation,carrying out researches on reservoir characteristics in the deepstrata is extremely significant for illustrating distribution of sand bodies and reservoirphysical property,and predicting favorable reservoir facies belt.The main researches of this thesis are reservoir sedimentary facies,distribution ofreservoir physical property and petroliferous property,and correlation of gas beds.These researches can provide sufficient theoretical foundation for comprehensivereservoir evaluation and prediction of favorable reservoir facies belt.1.The main rock types and sedimentary evolutionThe color tone of rocks of Yingcheng Formation in Siwujiazi oil field is dark.Most of rocks are gray,dark gray and gray black.The study area developed a set ofterrigenous clastic rocks mixed with a small quantity of pyroclastic.Vertically thelithological succession showed interbed of sand and mud.The study area developed typical fan delta-lacustrine depositional systems duringthe development of Yingcheng, there are eight microfacies in this area which containsubmerged distributary channel, branching mouth bar, interchannel, distal bar, sandsheet of fan delta front subfacies,and subaqueous fan,turbidity current,still water mud of shallow to semi-deep lake subfacies.Yingcheng Formation was equivalent tothe stage of lake basin expansion,but there was a small-scale lake regression duringthe development of YcⅡ.2.Distributing feature of reservoir physical property and petroliferous propertyAfter analysing log interpretation and physical property data of core samples,weconcluded that the reservoir of Yingcheng Formation is low-middle porosity and lowpermeability reservoir.On the plane the reservoir physical property and petroliferousproperty showed obvious zonations,and significantly decreased form top to bottom inthe vertical direction.3. Analysis of main control factors of reservoir physical propertyReservoir physical property of Yingcheng Formation in Siwujiazi oilfield iscontrolled by both of sedimentary facies and diagenesis. Reservoir quality of thebranching mouth bar and submerged distributary channel located in fan delta front arethe best,subaqueous fan is the second,distal bar and turbidity current are the worst.Diagenesis either improved pore structure of reservoir,or make it bad.Compactionand cementation can decrease reservoir porosity,dissolution can increase reservoirporosity.4.Distributing feature of gas beds and analysis of gas poolOverall,there are a large number of gas beds in Yingcheng Formation,and theydistribute in a long range vertically.Gas beds are concentrated in the first and secondMember of Yingcheng Formation,and distribute stably.The number of gas beds in thethird Member is fewer than the two Members above-mentioned,and the connectivityamong gas beds gets worse.The number of gas beds in the forth Member is the fewestof all,and the connectivity is the worst.Controlled by all of resource structure,regionaltectonic and faults laterally,gas is concentrated in different fault blocks located in thecore of regional anticline.Because Siwujiazi oilfield was controlled by both of sedimentation and tectonic,the types of gas pool are various,but the primary is structural pool.The study areaextensively developed fan delta-subaqueous fan depositional systems during thedevelopment of Yingcheng,which can provided favourable sedimentary environment for the formation of lithologic traps,so there are lithologic pool and structural-lithologic pool too.5. Reservoir comprehensive evaluationAccording to comprehensive evaluation of Yingcheng Formation reservoir,weclassify the reservoir as TypeⅡ and TypeⅢ,then classify TypeⅡ as TypeⅡAandTypeⅡB.Overall,TypeⅡ is dominated in this area,TypeⅢ is spread limitedly,TypeⅡBis spread more extensively than TypeⅡA.