Study On Volcanic Rock Geology-Geochemistry And Pool-forming Control Action In Dapingfang Area Of Liaohe Oil-field

The paper that begins with the study to the formation and distribution of Tertiaryvolcanic rock in Dapingfang area, Liaohe oil-field, analyses the relationship betweenvolcanic rock and hydrocarbon pool-forming in research area. On the basis ofgeochemical analysis for volcanic rock, connecting with observation and descriptionof drilling cores and microsection by microscope define the lithology and texture ofvolcanic rock, and then confirm classification, lithofacies, such as overflow facies,transition facies, and lithofacies characteristic;Tectonic and depositional settings,when volcanoes erupted, are displayed by variable tendency of main element content,eruptive stages and times of multicraters is classified tentatively by specimenclustering method, the research result reconstructs regional geology characteristic thatmulticraters erupting more than one time makes volcanic strata overlying. Moreover,the relationship between volcanic rock and three pool-forming factors, including oilsource rock, reservoir strata and cap rock, determined the different types of volcanicrock typal reservoir (a kind of oil and gas reservoir relates to volcanic rock), finally,conclusion points out the beneficial combination of generation, accumulation andsealing.The study shows that volcanic magma origin has relatively no change, and comesfrom mantle source areas, which have similar geochemical characteristic, the volcanicrock erupted during the depositional period of Dongying division 2 contrasts withother period, so the relative hasty mantle diapir penetration in this period is relatedwith intensive basin extending and chasmic stage. Rock types include basalt,trachybasalt, alkaline basalt, andesite and andesibasalt, which belong toalkalinity-weak alkalinity rock series, and give priority to neutrality-basic volcanicrock, that indicate the tectonic setting of continental rift. Because of the long distancefrom volcanoes, volcanic rock facies types mainly include: eruption facies, overflowfacies and volcanic sedimentary facies. During the process of magma evolution,craters moves towards the south. Volcanic rock from two eruptive sources,Taoyuan-Hongxing and southern Dapingfang, weaves and superimposes reciprocallyin strata. It is the significant characteristic of volcanic geology in Dapingfang area.Geochemical identification supporting with cluster analysis method yields the divisionof eruptive stages and 3 cycles including 6 times. The function of volcanic action foroil and gas accumulation is divided into four aspects: abnormal thermal evolution ofhydrocarbon source rock, volcanic rock reservoir, volcanic cap rock and the history ofvolcanic action relating to pool-forming. Judging by the function of volcanic rockacting in the process of generation, accumulation and sealing, the study obtains sevenkinds of trap patterns for volcanic rock typal reservoir of oil and gas, one kind ofcombination types is self-generation and self-accumulation, the other isunder-generation and up-accumulation, totally, there are nine kinds of beneficialcombination of generation, accumulation and sealing. In view of the wide range ofvolcanic rock and the reality of exploration activity, this research proposes the soundbase for next objective exploration.