Volcanic Rock Reservoir Features With Emphasizing On The Lithology Of The Upper Carboniferous Batamayineishan Formation In The Eastern Junggar Basin

The volcanic rock of Batamayineishan Formation in Eastern Junggar basin has great oil and gas exploration potential. Some large gas fields, such as Wucaiwan gas field, Kelameli gas field have been discovered since 1995. However, due to the limitation of lithology classification scheme, clear understanding of the reservoir physical property of each volcanic rock has not been formed, which restrict the exploration of the volcanic rocks in the region to a certain degree.In this paper, on the basis of previous studies, the lithology and reservoir characteristic and their relationship of volcanic rock in Batamayineishan Formation have been studied by means of profile survey, core observation, rock-mineral determination and the casting thin sections observation, geochemistry, Electron microprobe analysis(EMPA), physical property test. Primary understanding and the conclusions are as follow: 1. Volcanic rock Lithological characteristicsAccording to the "genetic mechanism- the content of SiO2- structure and mineral" lithological classification scheme, the volcanic rocks of Batamayineishan Formation can be divided into 4 genetic types, 5 component categories, 31 specific lithology. According to the type section, lava contributes 68.5% of genetic types, mafic and acidic volcanic rocks contribute 42% and 36% of component categories respectively. Basalt and rhyolite contribute 27.5% and 24.9% of specific lithology respectively, in addition, andesite contributes 7.3%. 2. Volcanic rock reservoir space types and combinationDepending on the stage of diagenesis, the volcanic rock reservoir space of Batamayineishan formation can be divided into primary reservoir space and secondary reservoir space. Primary reservoir space is divided into primary pores and fissures, primary pores include primary vesicular pores, amygdule inner pore, lithophysa cavity hole and amygdule shrinkage hole and the frame pore. Primary fissures including shrinkage fissure, cleavage fissure and inner-phenocryst fissure, the secondary reservoir space is also divided into secondary pores and secondary fissures, secondary pores include devitrification pore and dissolution pore. Secondary fissures include tectonic fissures and dissolution fissures. The volcanic rock reservoir space combination of Batamayineishan Formation can be divided into 7 types. 3. Modification of volcanic reservoir spaceThe space of volcanic reservoir is affected by the late filling and dissolution. According to the thin sections observation and electron microprobe analysis(epma), filling minerals mainly include silica(opal, quartz, chalcedony), calcite, zeolite(chabasite, analcime, clinoptilolite), saponite and chlorite(clinochlore, corrensite, chamosite), celadonite, prehnite, pumpellyite, iron-mineral and some other kind of mineral. Pore filling combination can be divided into 12 types. Solution is usually found in calcite, zeolite and some other pore and fracture filling minerals. 4. Volcanic rock reservoir property difference between basin margin and intrabasin and its reasonThe volcanic rock reservoir property in the basin is better than that at basin margin. The reason may be related to formation water, organic acids and some other fluid that widely exist in the basin. And because of the high temperature and pressure in the basin, the reaction speed has been quicken, which benefits the development of secondary pore and fracture; Also influenced by hydrothermal process, result in alteration in the matrix and phenocryst, in this way, rock density reduce and the reservoir property improve. 5. The volcanic rock reservoir property and its relationship with lithology and oil-gas possibilityThe Volcanic rock physical property of Batamayineishan Formation in Eastern Junggar basin has a good correlation with its oil-gas possibility, the volcanic rock that has good reservoir property always has good oil and gas showing. For example, rhyolite, vesieular amygdaloidal andesite, rhyolitic breccia lava, andesitic agglomerate lava, rhyolitic breccia and sedimentary volcanic breccia.