The Research On Volcanic Sequence Stratigraphy And Its Effect On Reservoir In Eastern Sag Of Liaohe Basin, NE China

Tectonic activity was frequent in Liaohe Basin during Cenozoic. Volcanic rocksof each period are overlaid spatially. This paper made a research on characters ofvolcanic stratigraphic sequence by using volcanostratigraphy method, making use ofconventional well-logging curves and three-dimensional seismic section, core data,slices and so on. And based on the study of relationship of facies-stages-reservoir,some relevant theories support for volcanic reservoir exploration could be provided inthis area, which could lay a solid foundation for comprehensive evaluation of volcanicreservoirs in Eastern Sag.This research use the data of cores to divide and identify the volcanic rocks’lithology and lithofacies, and divide Cenozoic volcanic rocks in Eastern Sag into threecycles and15stages based on drill dates combined with character of well logs andseismic profile. The eruptive intension of cycle1is strong. It changes from weak tostrong. The layer of volcanic rocks is thick-bedded. It is an incomplete cycle. Theeruptive intension of cycle2is also strong, but weaker than cycle1. It changes fromweak to strong and then to be weak. And the layer of volcanic rocks is alsothick-bedded. The volcanic rocks composition changes from mafic volcanic rocks tointermediate-alkaline volcanic rocks and then mafic volcanic rocks. It is a competesequence, and shows rhythm. The character of cycle3is similar to cycle2, the eruptive intension is weaker. It changes from weak to strong and then to be weak. Thelayer of volcanic rocks is thin-bedded. The volcanic rocks composition changes frommafic volcanic rocks to intermediate-alkaline volcanic rocks and then mafic volcanicrocks. It is a compete sequence, and also shows rhythm. The centre of thicknessmigrates southward from cycle1to cycle3. Tectonic activity in this area showssegmentation and multi-stage activities, and makes the centre of thickness migratesouthward. In the longitudinal direction, overlapping relationship ofmafic-netural-mafic is influenced by the evolution of magma.The result shows that volcanic lithofacies and Stages have certain effects onvolcanic reservoir. Through research of the relationship of lithofacies with porosityand permeability of volcanic rocks, we can see that the physical properties of volcanicrocks data show some deterioration trend with the changes of volcanic lithofacies. Inthis area reservoir property can be divided into three categories according to thesubfacies. Overflow facise-composite lava sub-facies and extrusive facies have betterproperties. The former shows better physical property，because the primary porosityrelatively developed. Well the extrusive facies are mai nly developed in the dome oftrachyte which are mainly dominated by light-colored mineral. They have thecharacters of brittle and medium strength, which is conducive to the formation anddevelopment of tectonic fractures, so they show good physical properties.Compaction effects on porosity and permeability of sedimentary rocks is moreobvious than volcanic rocks. When the depth>3km, volcanic rocks have moreadvantages than the sedimentary rocks. The research of the relationship of stage withporosity and permeability of volcanic rocks shows that volcanic rocks of S3q3stage isthe main oil and gas reservoirs, having the best properties. Porosity and permeabilityvalues of volcanic rocks shows a negative correlation with the distance from rock tothe interface. The closer distance between rock and the stage interface, the better reservoir physical property. Reservoir generally forms within200m from one stageinterface. Analyze the reasons, probably because each stage interface will sufferedreformed-weathering-leaching processes, during intermittent period, which improvephysical condition. Secondary reserving pores such as solution fissure is developed.In this area reservoirs are mainly developed in the vicinity of the top of each stage.