Sedimentary Characteristics And Reservoir Prediction Of The Ying2 Member In The Lower Cretaceous In Yingtai Depression

Yingtai depression which locates in Western Fault Basins Belt of West Songliao Basin is an asymmetric double-fault fault basin. Ying2 member of the Lower Cretaceous Yingcheng formation deposited a transional lithology between the volcanic rock and the terrigenous clastic dedimentary rock,giving priority to sedimentary pyroclastic rocks and sedimentary rocks.Previous study has done little on this and no unified research methods has been formed.Based on the well logging,seismic interpretation, and on the basis of core description, the depositional filling mechanism of pyroclastic rock is separated from normal terrigenous clastic rock.Combined with regional tectonic background and basic data analysis,it is thought that the second member of the yingcheng formation is controlled by the dual role of lake basin evolution and volcanic eruptions.Three stages of basin evolution,synchronizing with volcanic action,has the characteristic of volcanic sedimentary type sequence,thus the sequence stratigraphy method can be applied to study the sedimentary characteristics of Ying2 formation.It is considered that Ying2 member has a complete third-order sequence and composed of lower system tract, lake transgressive system tract and highstand system tract.Meanwhile,according to the effect on the work area, two regional volcanic eruption is recognized, furtherly divided the Ying2 formation to five level 4 cycle, from bottom to top respectively are C1, C2, C3, C4, C5 cycle. Using geological and geophysical methods, it is determined that the sedimentary pyroclastic rocks of Yingcheng formation has two input source,namely the contemporaneous volcanic clastic source and proximal terrigenous clastic source. Volcanic clastic source mainly comes from south of the sag while proximal terrigenous clastic source comes from the uplifted side of western fault and northern long span.Ying2 member mainly locates in the lake facies sedimentary environment.according to core facies,logging facies and seismic facies analysis,it is discovered thatthe objective layer developed 7 facies,namely alluvial facies,fan delta,braided river delta,limnetic facies,littoral and shallow lake facies,deep lake facies and volcanic sedimentary facies.The degree of how much the facies are affected by volcanic action are obviously different.Combined with the sedimentary characteristics of each cycle,the spatial evolution law of the volcanic sedmented basin’s sedimentary system is summarized and sedimentary patterns is established. south volcanic mainly erupts in early and late stage of fault basin subsidence;Fan delta is distributed along the the steep slope of the fault depression on the west side and is formed when volcanic in the up-throw side of fracture-controlling fault accumulates rapidly after erosion in the lake;Braided river delta develops during the early base-level falling period after the lake expansion,formed when pyroclastic material sedimented in the shore shallow lake after the water flow carried it along the long axis of the fault depression from the north to south.In reservoir prediction,through the analysis of the logging curve intersection chart,it is found that density curve best matches the sensitivity of beneficial reservoirs in Ying2 member of Yingtai depression so it can used as the best rock physical attribute to identify reservoirs. curve reconstruction and synergy geologic modeling method are used to forecast effective reservoirs in the work area, it is predicted that fan delta front,braided river delta,volcanic-affected shore and shallow lake and marsh are favorable reservoir,tuffites and breccia rocks are favorable reservoir.The reservoir distribution is mainly affected by the volcanic rocks in place and the thickness of,tuffite and tuffaceous breccia.