基于卫星重力异常的南海南部中生界反演

Mesozoic Distribution Derived from Satellite Gravity Anomaly in the Southern South China Sea

已有钻井以及地震资料揭示南海南部海域广泛发育中生代地层。为了进一步了解南海南部中生代地层的分布特征及油气地质意义,本文利用最新的卫星重力数据反演中生界的深度和厚度。首先,采用重力场正演技术消除海水的影响,获得南海南部布格重力异常。其次,为了消除新生代沉积层的影响,将新生代沉积层划分为0~3、3~6、6~10 km 3层,并根据前人在南海获得的密度与深度的关系,采用变密度Parker正演方法计算新生代沉积层产生的重力影响,并将其从布格重力异常中减去,从而获得前新生代重力异常。在此基础上,采用小波多尺度分解技术,消除深部莫霍面以及局部岩体重力的影响,从而计算得到反映中生界的重力异常。最后采用三维Parker变密度界面快速反演技术获得南海南部中生界深度和厚度。反演结果与已知中生界钻井具有较好的对应。南海南部地区中生界主要分布在礼乐滩、巴拉望岛北部和万安地区,厚度分布小于9 km,其他大部分地区中生界厚度小于1 km或者不存在中生界。其中中生界在礼乐滩地区最为发育,其次在巴拉望岛北部也广泛发育。结合前人在该区域的油气地质条件研究成果,认为南海南部海域礼乐滩地区中生界具有较好的油气勘探前景。

Existing drilling and seismic data reveal that Mesozoic strata are widely developed in the southern South China Sea(SCS).In order to further understand the distribution characteristics and oil and gas geological significance of the Mesozoic strata in the southern SCS,the latest satellite gravity data are used to invert the depth and thickness of Mesozoic strata in this paper.Firstly,the gravity field forward modeling technique is used to eliminate the influence of the sea water,and the Bouguer gravity anomaly in the southern SCS is obtained.Secondly,in order to eliminate the influence of the Cenozoic sedimentary layer,this layer is divided into three layers:0-3 km,3-6 km and 6-10 km.According to the relationship between density and depth obtained by predecessors in the SCS,the gravity influence of Cenozoic sedimentary layers is calculated by using the variable density Parker forward modeling method,and it is subtracted from the Bouguer gravity anomaly.The Pre-Cenozoic gravity anomaly was obtained.On this basis,the wavelet multi-scale decomposition technique is used to eliminate the gravity influence of deep Moho and local rock mass,so as to calculate the gravity anomaly derived by Mesozoic strata.Finally,the depth and thickness of Mesozoic strata in the southern SCS are derived by using the 3 D Parker variable density interface fast inversion technique.The inversion results correspond well with the known Mesozoic wells.The Mesozoic strata in southern SCS are mainly distributed in Liyue Bank,the north part of Palawan Island and Wan’an area,with the thickness less than 9 km,while in most other areas less than 1 km or no Mesozoic strata.The Mesozoic is the most developed in Liyue Bank area,followed by the northern part of Palawan Island.Combined with the previous research results of oil and gas geological conditions in this area,it is concluded that the Mesozoic of Liyue Bank area in the southern SCS has a good oil and gas exploration prospect.