含油气球冠模型三维重力归一化总梯度场特征

CHARACTERISTICS OF THE THREE-DIMENSIONAL NORMALIZED FULL GRADIENT FIELD OF GRAVITY ANOMALY IN THE OIL SPHERE CORONAL MODEL

重力归一化总梯度的三维计算中,将圆滑滤波因子分别引入向下延拓和导数换算响应因子中,推导了其计算公式及数值实现过程,同时给出了具体的计算步骤;对含油气球冠模型的三维归一化总梯度场特征进行了分析与研究。研究结果表明,对于含油气球冠模型来说,不同于均匀球冠模型在各个深度的切平面等值线图中表现出单峰异常的特征,其三维归一化总梯度场的特征表现为:无论在过中心剖面的等值线图还是在某个深度的切片图中,只有当截止频率取值适当时才可以表现出"两高夹一低"的典型储油气藏标志特征,若取值不当,其表现出来的特征与均匀球冠模型相似。此外,归一化总梯度场等值线图中出现"两高夹一低"的位置,往往是含油气球冠所在位置和深度。

This paper introduces filter factors respectively in downward continuation and derivative calculation for calculating the threedimensional normalized full gradient field of gravity anomaly. The authors deduced the computing formula and the process for achieving its numerical value, and then gave the specific calculation procedure. Characteristics of 3D normalized full gradient of gravity anomaly in the homogeneous oil sphere coronal model were analyzed. It is concluded that, for oil sphere coronal, the 3D normalized full gradient field has the following features： no matter whether it is in a figure of central section or in that of a slice, only when the suitable cut-off frequency is obtained can the ＂two folders and one low＂ of typical characteristic signs of oil-gas reservoir be shown; otherwise, it is similar to the model of homogeneous sphere coronal which shows characteristics of a single peak anomaly. In addition, the position of ＂ two folders and one low＂ in the contour map of normalized full gradient field is usually the position and depth of the oil sphere coronal.