高分辨率层序地层学在北部湾盆地重点层系选段中的应用^*

Application of high resolution sequence stratigraphy to determination of key intervals in Beibuwan Basin

摘要

北部湾盆地是南海北部五大含油气盆地之一,油气资源潜力大、有较好的勘探前景,但是北部湾盆地三级构造单元海中凹陷古近系涠洲组地质研究程度较低、地层厚度大,严重制约了海中凹陷的油气勘探。高分辨率层序地层学在低勘探程度区域是一种有效的地层划分手段。依托三维地震资料、测井资料、岩心资料,在地震剖面二、三级层序界面和测井层序界面识别的基础上,采用最大熵谱分析、小波变换分析、岩心分析方法,对海中凹陷涠洲组进行了高分辨率层序识别与划分,研究表明最大熵谱分析对于三、四级层序界面具有较高的分辨性, 小波变换可以进行四—六级及更高级别旋回分析, 而岩心资料可以进行短期、超短期旋回分析。综合三维地震、测井、最大熵谱分析、小波变换技术和岩心资料将涠洲组划分为1个二级层序,包括6个三级层序、13个四级层序,并且根据13个四级层序含砂率对比,涠三段SQ6-LST四级层序含砂率最高,涠三段SQ6-HST四级层序次之,勘探潜力较大。本研究对低勘探程度凹陷重点层系选段具有一定指导意义。

Abstract

Beibu Gulf Basin is one of the five major oil-bearing basins in the north of the South China Sea, with great potential for oil and gas resources and good exploration prospects. However, little research has been done on the thick Weizhou Formation in the Haizhong Depression, the third-level structural unit of the Beibu Gulf Basin. This significantlyhinders the hydrocarbon exploration in the Haizhong Depression. High resolution sequence stratigraphy is an effective method for stratigraphic division in geographic exploration frontiers. Using 3D seismic, well logs and core data, and on the basis of identification of second-order and third-order sequence boundaries on seismic profiles and wells, this paper uses maximum entropy spectral analysis, wavelet transform analysis and core analysis methods to identify and subdivide the high-resolution sequences of the Weizhou Formation. The results show that the maximum entropy spectral analysis has high resolution for third-order and fourth-order sequence boundaries; wavelet transform can analyze fourth to sixth order cycles and higher order cycles; Core data can be used for short-term and ultra-short-term cycle analysis. Based on 3D seismic, well logging, maximum entropy spectral analysis, wavelet transform technology and core data, the Weizhou Formation can be divided into 1 second-order sequence that includes 6 third-order sequences, which are in turn composed of 13 fourth-order sequences. According to the comparison of 13 fourth-order sequences, the highest sand ratio occurs in SQ6 LST , which is followed by SQ6 HST, suggesting great exploration potential. This study indicates that high resolution sequence stratigraphy of multi-scale and multi-method has certain guiding significance for screening key intervals in depression with low degree of exploration.

关键词

小波变换 / 最大熵谱分析 / 海中凹陷 / 涠洲组 / 高分辨率层序

Key words

wavelet transform / maximum entropy spectral analysis / Haizhong sag / Weizhou Formation / high resolution sequence

基金资助

*国家科技重大专项“十三五”子课题(编号:2016ZX05026007-007)