琼东南盆地北礁地区梅山组丘形反射特征

摘要

Nowadays,a lot of mounded seismic reflections in the Mid-Miocene Meishan Formation were found and attracted the attention of geologists,while the genesises of the mound were various.Combined with the 3D high resolution seismic data and the 2D seismic datum and drilling,this paper aimed at analyzing the characteristics of the mounds.The results show that compared with the weak amplitude channel filled with mudstone in northeast 3D area and the high amplitude channel filled with sandstone in southwest 3D area,the elongated mounds with nearly EW orientaion had mediate amplitude.The channel located between mounds.Wave impedance inversion un-ravelled that the mounds with inner lower impedance should belong to the scope of mudstone.The inner mound bed with ductile within Meishan Formation were subjected to gravitational spreading,which contributed to devel-oped polygonal faults on the overlying strata with brittle property.Under this circumstance,Meishan Formation was concluded to form in deepwater depositional environment in Mid-Miocene and mounds on the top of Meishan Formation consisted of mudstone.Mounds and channels formed the sag-crest bedform corresponded with channels and mounds above the overlying strata,respectively,which was regarded as the result of bottom current of incision and deposition.This study about the Mid-Miocene mound reflections has guiding significance and can improve the success rate of oil and gas exploration drilling and can reduce oil and gas exploration risk.%目前琼东南盆地北礁凹陷中中新统梅山组顶部丘形反射引起广泛关注,但对其成因有不同认识.本文通过高精度二维、三维地震、钻井资料,研究丘形反射的特征.研究表明北礁地区梅山组顶部发育近东西向展布的长条形丘体,丘间为水道,丘内为中-弱振幅的地震反射,与西南部强振幅水道砂岩形成鲜明的对比,波阻抗反演揭示丘内为低波阻抗,属泥岩范畴.梅山组塑性丘内地层发生重力扩展,在其上覆的脆性地层(强振幅砂岩和弱振幅泥岩)发育多边形断层,反推出梅山组形成于深水环境,丘为泥丘,沉积环境分析也认为北礁凹陷中中新世为半深海沉积,梅山组的丘-谷分别对应上覆地层的谷-丘,认为是底流剥蚀/沉积成因.本文的研究对南海北部丘形反射的认识有重要意义,并可降低油气探勘风险.