Research On The Volcanic Rock Reservoir Characteristics Of Carboniferous Kalagang Formation In Malang Sag

Volcanic reservoirs characteristics of Carboniferous Kalagang Formation in Malang Sag was studied detailed based on the comprehensively utilized of core observation, thin section analysis, SEM, well logging data,3D seismic and the data of reservoir physical properties. At the same time, comprehensive reservoir evaluation and favorable zones prediction were done in this article.Volcanic lithology in the studied area is composed of intermediate-basic basalt, andesite and intermediate-basic transitional lithology. As the rocks were affected by the reconstruction of late diagenesis, alteration phenomenon occurred generally in the mineral; The volcanic facies can be divided into overflow facies, eruption facies, volcanic channel facies, extrusive facies and volcanic sedimentary facies, which is based on overflow facies, and the eruption facies are distributed with a string of beads, but the volcanic sedimentary facies distributed scattered relatively; Volcanic reservoir space is composed by primary and secondary porosity, and secondary storage space is often superimposed on the original storage space, and the pore, hole, slit woven together to form the effective storage space. With the analysis about volcanic diagenesis, thirteen diagenesis types are being existence in the studying area. Each type has different effect to the formation of volcanic reservoir, and there are two respects as constructive action and destructiveness; The phenomenon such as laumontitization, albitization, arfvedsonization, sideritation and SiO2 dissolving prove that the Hydrocarbon alkali fluid is obtained in the Carboniferous Volcanic rocks. The alkalic environment reveal that alkaline diagenesis in the Carboniferous volcanic rocks is common. Mineral components in the reservoir move because of alkali metasomatism. The vertical zoning laws of "alkali under the silicium" formed and saved a large number of secondary porosity, which would formed a large number of secondary pore zones and laid the mineralogy foundation for the formation of reservoir; Hydrocarbon alkali fluid and the late acid fluid play an important role for the formation of reservoir. The formation of volcanic reservoir in the study area shows that the formation mechanism of "early alkali late acid", the reservoir and seal system formation mechanism of "alkali under the silicium", weathering and leaching reservoir formation mechanism, unconformity reservoir formation mechanism and the migration, grooming and closed mechanism of discordogenic fault; The overall performance of the reservoir property shows that the andesite is the best, followed by the basalt. The formation of kinds of secondary pore plays an important role for the improvement of volcanic physical property; Volcanic reservoir in the study area is middle-low porosity and low and ultra-low permeability. The reservoir can be divided into four types, while the effective reservoirs types areⅠ,ⅡandⅢ, and there is a certain regularity for the area and horizon each type developed; The result of Volcanic Reservoir Prediction shows that the favorable reservoirs mainly develop in weathering crust zone, high-position tectonic the fracture developed and favorable reservoir facies the source-reservoir-cap contact closely. The small weathering crusts on the large volcanic edifice in parts of area are also favorable reservoir.