Volcanic Reservior Characteristics And Distribution In Wangfu Fault Depression Of Southern Songliao Basin

Since2009, deep volcanic rocks in Wangfu Depression have been becoming thefocus zone of gas exploration in jilin oilfield company and three sets of volcanic rockreservoir have successively been found in the bottom of Shahezi Formation andHuoshiling formation, initially forming one hundred billion gas reserves scale inHuoshiling, marking the deep volcanic reservoir in wangfu sag has a great explorationpotential. Along with further exploration,due to the lithologic complexity of volcanicrocks undergoing multiphasic complicated diagenesis in the sag,their reservoir spacetypes and reservoir characteristics have a big distinction,and effective reservoirdevelopment is controlled by many factors,so that to clarify the lithologycharacteristics of different volcanic reservoir and their distribution patterns becomesthe key of volcanic rock reservoir exploration in this area.This paper is based on previous research findings and existing explorationachievements,with the application of core observation, thin section identification,physical properties test, mercury injection and nuclear magnetic analysis technology,combining with seismic and logging data, we have analyzed the lithofacies, lithology,reservoir space types and reservoir physical characteristics of volcanic rock reservoirfrom huoshiling and shahezi formation in wangfu sag and then discussed the maingoverning factors and distribution pattern of volcanic rock reservoir. The achievementand conclusion are as follows:There are4types and24kinds of volcanic rocks in Wangfu sag. Trachyandesiteand trachyandesitic clastic rock make up the most. And rhyolitic volcanic rock andsedimentary pyroclastic rock make up a certain proportion. Four lithofacies and ninesubfacies are met. The main lithofacies is extrusive, the secondary eruptive，and thereis little volcanic vent facies and volcanic sedimentary facies. The reservoir space canbe divided into two types named original interstice and secondary interstice. There areten specific types of reservoir space,including primary pores, corrosion pores, grains(gravel) pores, intergranular micropores, mineral cracks, condensation contractionjoints, phenocrysts dissolved pore, matrix pore, dissolved fractures, Structural fracture.There are5types of effective reservoir space combinations. Different lithology has different reservoir space combinations. The main physical property of volcanicreservoir in studied area is medium-high porosity and medium-low permeability.The trachyandesitic breccia lava、 rhyotaxitic tufflava and volcanic breccia aremedium-low permeability reservoirs. The pore structure of volcanic reservoir can bedivided into four categories named Ⅰ/Ⅱ/Ⅲ/Ⅳ. The rhyotaxitic tufflava andtrachyandesitic breccia lava mainly belong to the categoryⅠ. The volcanic brecciamainly belong to the category Ⅱ.Three types of reservoir including trachyandesites/liparite/sedimentarypyroclastic rocks have been generated from bottom to top in the Wangfu sag. Theeffective reservoir is controlled by several factors, mainly including lithology,lithofacies, the types of volcanic apparatus, volcanic environment, tectonism,weathering leaching process and dissolution. Trachyandensitic volcanic rocks arecontrolled by volcanic apparatus, weathering denudation and tectonism. The highquality reservoir developes nearby the combined volcanic apparatus and faults whichare controlled by tectonic unconformity and eruption discontinuous unconformity;Occurence environment controls the development of rhyolitic volcanic rocks, thehigh quality reservoir mainly developes in the north of studied area and the reservoirquality from north to south gradually decreases. The high quality reservoir ofsedimentary volcanic breccias mainly distributes at CS6well area in the bottom ofShahezi Formation and WF1-CS9well area in Huoshiling Formation.