三维高精度重力方法在深部潜山勘探中的应用

APPLICATION OF 3D HIGH PRECISION GRAVITY METHOD TO THE EXPLORATION OF DEEP BURIED HILL

深层地震资料由于受到火山岩体或风化壳盖层的影响,质量品质往往不高,难以识别盖层之下的小规模的潜山构造。而重力勘探技术恰能利用潜山构造与上覆地层存在显著密度差异的特点来识别这种特殊的地质储层。文中以华北油田虎8北潜山构造区为例,在该地区地层密度模型的基础上进行了三维重力正演。正演结果表明,深部密度异常体在地表形成的低缓重力异常,与区域或局部背景重力异常场叠加在一起,在布格重力异常曲线上无法识别目标体异常。通过利用高阶导数、滑动滤波等处理方法把异常场从区域场中剥离出来,可发现虎8北潜山目标区存在小规模局部剩余重力高。在地震资料的约束下,根据剩余重力异常的幅值及地层密度差进行密度建模,实现了三维密度反演。反演的结果确定了虎8北潜山的存在,并给出了潜山可能的埋深与规模。证明了三维高精度重力方法在确定深部潜山构造上具有较明显的地质效果,这对于探测深部低速层覆盖之下的潜山构造油气藏具有重要的指导意义。

Due to the influence of volcanic rock or weathering crust coverage,the quality of deep seismic data is often not reliable and it is difficult to identify small deep buried hill structure beneath the cover. However,the gravity exploration technology can use the remarkable density differences between the object and the overlying strata to identify this special geological reservoir. Although recently several rounds of seismic exploration have been carried out in Raoyang depression,Huabei Oilfield,North China to determine the existence of Hu 8 north deep buried hill,whether the buried hill really exists or not as well as its scale is still in controversial. In this paper,based on the information of seismic data and formation density,deep processing of 3D high precision ground gravity data has been carried out for 3D forward and inversion computation. The dimensional gravity forward calculation results show that the density of the deep anomaly body forms a relatively low gravity anomaly in the earth＇s surface. By using the potential processing method of vertical second derivative,and sliding filtering,the residual anomaly is separated from regional or background field,which illustrates the existence of a local high gravity anomaly at Hu 8 north area. According to the amplitude of residual gravity anomaly and formation density difference modeling,through a number of 3D forward calculations and 3D inversion of gravity data,the existence of Hu 8 north buried hill and its possible scale are basically determined. The results prove that the 3D high precision gravity method is effective in determining the deep buried hill structure in case that seismic data is not reliable.