测井资料Xu-White模型预测横波速度的一些新观点

New Viewpoints on S-wave Velocity Prediction Using Xu-White Model Based on Well Logging Data

目前横波预测的方法大致可以分为两种:经验公式预测和理论岩石物理模型。由于经验公式预测一般具有区域性,研究者更重视岩石物理模型预测。目前大多数岩石物理模型预测横波的方法假定地下流体的物性参数(速度和密度)不受地层深度的影响,且孔隙扁率是恒定的,实际上这并不科学。因为矿物的体积模量和剪切模量随所处地层深度发生改变,而对于孔隙扁率则随颗粒形状、孔隙度等的变化有较大变化。针对这些情况,提出一种新的改进的Xu-White横波预测方法,并可取得较好的效果。

Physical quantities such as the Poisson ratio and Lame modulus,which represent fluid properties,can be obtained using S-wave velocity.These parameters can be used to reduce the multiple interpretations of seismic amplitudes.Thus,although it is very important to use S-wave velocity in performing seismic data AVO analysis,prestack inversion,and fluid identification,there is seldom information about this velocity in actual logging data.Currently,methods for Swave velocity prediction can be divided into two types：empirical formula method and theoretical rock-physics-model-prediction method.The former is simple,limited to some exploration area,and requires larger workloads to increase its general overall applicability.Compared with the empirical formula method,the rock physics model method is complex,but it has universal application in different areas.Most rock physics model methods for predicting S-wave velocity assume that the physical parameters of an underground fluid（velocity and density）are not affected by the depth of the stratum or pore aspect ratio.However,this is not a valid assumption even for the most popular rock physics model,the Xu-White model.In fact,the bulk modulus and shear modulus of minerals change with the depth of a reservoir.For fluid parameters,this type of effect will increase.With respect to the pore aspect ratio,its change is fundamentally related to the particle shape formation pressure and porosity,i.e.,it is not constant.The aspect ratio has clearer geological implications：bigger aspect ratios correspond to reservoirs with higher porosity and permeability,and lower aspect ratios correspond to reservoirs with lower porosity and permeability.In addition to these parameters,most studies have also neglected some assumptions for the prediction of S-wave velocity.In this study,we investigate these assumptions and present a new and improved Xu-White method.We all know that the compressional wave time difference,S-wave time difference,and mineral formation density are affected by depth,which is usually neglected.Tolerance stacks may be large in some special geological situations,which should be investigated by geophysicists in the future.