The Character Of Reservoir And Distribution Prediction Of Volcanics In Chagan Sag

Chagan Sag locates in the center of Chagandelesu Depression in the east of Yingen-Ejinaqi Basinand it is subjected to Wulatehouqi of Neimenggu province. After 50-year exploration, somesuccesses have been obtained through the petroleum explorations and studies, but there remainslots of geological problems to deal with, such as evolution of structure-sedimentary in ChaganDepression, the types, the log response, the distribution of the volcanic rock, the ability topreserve petroleum of the volcanic reservoirs and the formation of the reservoirs etc.Under the guidance of theories like volcanics lithology, reservoir geology and petroleum geologyand based on the analysis of volcanics types and log response, this paper studied the accumulationability of volcanics, used the impedance inversion of reconstruction by Acoustic and Gamma withthe restriction of multiwell, predicted the distribution of volcanic rocks and finally discussed thequalifications of the formation of reservoirs.It is considered that volcanic rocks are mainly developed in Group Suhongtu. There are volcanicbreccia, basalt, andesite and tuff in this area in which basalt distributed the most abroad, and thereare sedimentary interlayers in volcanic rocks, forming a duality structure.There are many types of reservoir space in volcanic reservoirs and many forms of combination arecoexistent. The pores and fractures in the reservoir are heterogeneous with lower average aperture,worse connectivity and lower average permeability. So the reservoir is of low porosity andpermeability.To distinguish from clastic rock and mudstone, the volcanic rock is characterized by high density,high resistance, high self-potential, low gamma ray and low acoustictime in well logging curves,with gamma ray curve distinctly low. Because of the limitations of single well log, cross plot isused to identify volcanics lithology.According to the distribution prediction and area geology data, the volcanic rocks distributedalong the faults, and they had two eruption pots. One is near well mao4 and the other is by wellchacan1.According to the analysis of formation of reservoir, the dominant source rock distributed in thesecond sect of Group Bayingebi, with abundant oil sources and preferably type. Affected byvolcano movements, the door limit of maturity here is relatively low. Volcanic rocks that developpores and fractures are able to accumulate petroleum while the compact volcanic rocks are to becap rock, and the main source-reservoir-cap assemblage is lower-generation andupper-accumulation type.