Magmatic Activities In Petroliferous Basins And Their Reservoir Significance

Igneous reservoir,as a special type of oil and gas reservoir,has been paid more and more attention by geologists and petroleum scholars in recent years.The development of igneous reservoir is closely related to the corresponding magmatic activities,a large scale of Mesozoic and Cenozoic igneous rocks was developed in Huanghua Depression,and the igneous reservoir is considered to be one of the most important targets for exploration and development of oil and gas in the future.It is of great significance for the exploration and development of oil and gas and the improvement of the theory of igneous reservoir to carry out the study on the Igneous identification,magmatic activity sequence distribution law and main controlling factors of magmatic reservoir in basins.Based on core observation,whole rock geochemistry,zircon U-Pb geochronology,scanning electron microscopy and conventional porosity and permeability analysis,and combined with logging,drilling,seismic profile,oil test and production test data,the igneous rock types,magmatic activity sequence and characteristics of igneous reservoir space are analyzed in detail,the reservoir development model is established and its main controlling factors are discussed,and the reservoir distribution in two areas is predicted at last.(1)Five categories and 19 types of igneous rocks are confirmed in Huanghua depression.The crosslogs can accurately distinguish the types of igneous rocks.Basic rocks are characterized by low gamma,high density and high wave velocity,neutral rocks are characterized by medium gamma,medium density and high wave velocity,and acidic rocks are characterized by high gamma,low density and medium wave velocity.(2)4 cycles of Mesozoic igneous activities are identified in Huanghua depression.The Mesozoic magmatism in Huanghua depression started in 140.1±1.4 Ma and could be divided into two stages including the Early Cretaceous stage and Late Cretaceous stage.The Early Cretaceous magmatism principally developed basic-intermediate rocks in the north zone,and could be subdivided into 3 stages with their forming ages of 140-135 Ma,125–114Ma,and <114 Ma,respectively.By contrast,the late stage mainly developed intermediate-acid rocks centralized in the south zone and formed at 75–70Ma.stage 1 and 3 mainly developed basalt,stage 2 developed andesite and stage 4developed dacite.(3)The first stage is fissure eruption with low weathering degree and no reservoir developed.The magma was central erupted in Koucun area and Wangguantun areas,while fissure erupted in Qibei area,high quality reservoirs are distributed in weathering crust in Koucun area.The basalt of stage is fissure erupted with wide area and small thickness,and thin weathering crust type reservoir was developed.The dacite is concentration distributed,and the reservoir distributed in the subfaces of top and bottom belts of the rock.(4)The lithologic facies of igneous rock controls the distribution of reservoir in volcanic mechanism.Weathering and leaching can obviously improve the reservoir physical properties and affect the thickness about 100 m.Tectonism makes the footwall of the fault easier to form reservoir and increases the reservoir depth.The rocks close to the fault developed higher degrees of fractures.(5)Different stages of diagenetic evolution directly affect reservoir properties.The vesicles would be filled in the late stage of syngenesis and superdiagenesis,while supergenetic and burial weathering lead to the formation of tectonic fracture could obviously enhance the reservoir properties.The reservoir properties were improved of stage 2 in the Supergene and burial stage.The reservoir properties improved in stage 4in the Supergene and burial stage due to the fractures.The basalt in Zaoyuan area is shallow buried and weakly filled in burial stages,thus preserved the pore spaces and formed high porosity reservoir.(6)Igneous rocks of stage 2 developed weathering crust-eruptive facies type reservoir with high porosity medium permeability,the stage 3 igneous rocks developed weathering crust-effusive facies type reservoir with medium porosity medium permeability,the 4th stage 3 developed fault-weathering crust type reservoir with medium porosity low permeability.The basalt of Cenozoic developed vesicle-fractured reservoir with high porosity low permeability,and the gabbro and Andesitic porphyrite developed fault-weathering with low porosity and low permeability.(7)The prediction of high-quality reservoir requires comprehensive analysis of lithologic lithofacies volcanic mechanism and reservoir influencing factors.Multiple approaches combined with offset well characteristics,another crust-eruptive facies type reservoir is predicted in Koucun area.What is more,crust-eruptive facies type,vesiclefractured and fault-alternated reservoir simultaneously developed in Binhai area.