| Chaoshan depression is located in the southeast of the pearl river mouth basin in the north of the south China sea,which develops a large number of Mesozoic igneous rocks.Well LF35-1-1 is located in the draping structure LF35-1 in the northwest of Chaoshan depression,which is an exploration well revealing complete Mesozoic horizon and great thickness in Chaoshan depression.Well LF35-1-1 is the main data source of this study.Combining with a variety of indoor tests and analysis methods at the same time,this research mainly based on the detailed description of cutting thin section observation.Making use of petrology,petrography,geochemistry and chronology,the study clear the igneous rock lithology and lithofacies sequence,formation time and tectonic environment of reaction of research area and make sure the influence brought by magmatic activities to the evolution of hydrocarbon source rocks,reservoir development and oil and gas gathering.There are a lot of igneous rocks developed in the Mesozoic of chaoshan depression.According to its occurrence,it can be divided into shallow intrusive rock,deep intrusive rock,volcanic lava and pyroclastic rock.Among them,basic rock,neutral rock and acid rock have been found but no ultrabasic rock,which develop complex texture and structure.Basalt and andesite are mainly developed in lower cretaceous.The middle-upper Jurassic is mainly granite and granodiorite.According to cuttings logging data,cuttings thin section data,logging data,geochemical analysis data and seismic data,igneous rocks in the study area can be divided into intrusive facies,eruptive facies,overflow facies and volcanic sedimentary facies.The Jurassic cretaceous igneous rocks in well LF35-1-1 can be divided into 6 cycles from bottom to top,with nearly 20 periods.The Jurassic can be divided into five cycles,each of which contains several periods.The lower Cretaceous is divided into one cycle and five periods according to the internal structure.Mesozoic igneous rocks in well LF35-1-1 are characterized by relative enrichment of large ion lithophile elements like Rb,Ba,Th and U and relative loss of high field strength elements Nb,Ta and Ti.The rittman index of the sample is less than 3.3 belonging to calc-alkaline rocks.In the standard diagram of chondrite meteorites,the basalts all show the same LREE right-leaning enrichment type distribution mode,and light rare earths had obvious differentiation,without obvious Eu anomaly.The distribution patterns of granite chondrite meteorites are consistent.They are all right-dipping distribution of light rare earth relative to heavy rare earth enrichment,with extremely weak Eu negative anomaly.The curve is steep to the left and gentle to the right,with a slight upward-sloping tail,which is shaped like a shovel,reflecting the separation and crystallization of amphibole in the magma source area.Most of the igneous rocks erupt in the middle Eocene,and the intrusive stage is the late cretaceous.The magmatic activity in the middle and late Jurassic of Mesozoic is weak,which means this period is a quiet period of tectonic activity.The thermal evolution of organic matter in source rocks has entered the over-mature stage,and the maturity of organic matter near intrusive rocks is higher.Therefore,it is believed that the over-maturity of organic matter in source rocks in this area is mainly affected by late magmatic activity.The homogenization temperature of the inclusions at the top and bottom of well LF35-1-1 is basically consistent with the thermal evolution degree of the hydrocarbon source rocks reacted by vitrinite reflectance,which indicates that the thermal evolution degree of the organic matter in the hydrocarbon source rocks has indeed entered the overripe stage.The turbidity zeolite produced by magmatic activity can affect the reservoir conditions in both directions. |
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