Study Igneous Rock Distribution Of Northern South China Sea By Using Gravity And Magnetic Method

The northern area of South China Sea is closed to south of China Mainland. There are different types basins formed on the margins of the South China Sea in Cenozoic, which are rich in oil-gas resources. Thus far, many large and medium oil-gas fields have been discovered only in the shallow water area of northern South China Sea, and production is increasing. The results of oil-gas exploration in recent years show that part of oil-gas fields development with igneous rocks. Development of igneous rocks is advantageous to converted source rocks to hydrocarbons, it accelerates petroleum accumulation, and it also can damage reservoirs. On the whole, the promotion effect of magmatic activity is greater than the destructive effect. Hydrocarbon reservoirs related to igneous rocks are played more and more attention after substantial discovery and development. Thus, studying distribution of igneous rocks of northern South China Sea can provide basis for later oil-gas exploration.There are decades of exploration history with high degree of exploration in land and marine shallow water area in China. The deepwater area also has abundant resources. Because of lack of geological understandings and development techniques, the oil-gas exploration in deepwater area of South China Sea keeps ticking over. Because of seismic reflection images vague, drilling working difficult, and high-tech, high-investment, high-risk, it is controversial in geological understanding. It cause that exploration direction is not clear and exploration is difficult to work. Satellite gravity and aeromagnetic data are wide coverage, low cost and good effect, and unfold the research value in the study of the regional geology.The author collected gravity, magnetic, seismic profile data, regional geologic data of northern South China Sea. This dissertation mainly uses methods in gravity and magnetic data processing, and by using new the potential field data processing methods, got high-precision anomalies data, highlighted anomalies of igneous rocks, and increased the results reliability. The main studies and achievements of this dissertation are as follows:(1) I used some methods to eliminate or reduce the influence of water depth, sediments and oblique magnetization, including Bouguer correction, deposition correction, and reduction-to-pole at low latitude.(2) I used methods for anomalies separation and anomalies enhancement, extracted the weak information in superimposed anomalies, improved the discernment and increased the results reliability.(3) Different lithological rocks has the differences properties in density and magnetic. I extrapolated stratigraphic lithology and distribution of igneous rocks by making full use of that property.(4) In order to verify the reliability of results, I took full advantage of seismic data and geological information to launch the analysis, and built geological modeling by jointing gravity, magnetic and seismic data.(5) The analysis results show that the magmatic activity gradually enhances from the Qiongdongnan Basin to the Pearl River Mouth Basin; the scale of volcanic rocks increases gradually, and the age tends to be younger from shallow water area to the deepwater area in the northern area of South China Sea. The volcanic rocks provide favorable conditions for hydrocarbon accumulation, so they are important targets in the deep exploration.