核磁毛管压力曲线构造方法综述

Review of methods for constructing capillary pressure curve by NMR logging

核磁共振(NMR)测井数据的一般解释方法是将NMR信号分为快速衰减部分和慢衰减部分,与此相对应将储层流体分为束缚流体和可动流体,划分的主要依据是弛豫时间T2截止值。为了能在井下连续获取毛管压力曲线,可以将NMRT2分布直接转换成毛管压力曲线,但孔隙中烃的存在对T2谱的形态影响较大。文章就目前国内外NMR毛管压力曲线构造方法以及含烃情况下核磁T2谱形态校正方法作了详细阐述。

The usual interpretation method of NMR data is to divide the signal into a fast relaxing part and a slow relaxing part.The reservoir fluid can be divided into the bound water and the mobile fluid,for example,mobile water and/or hydrocarbons.The split between these two parts is made by applying T2 cutoff.In sandstone,the T2 cutoff is equal to 33 millisecond,and its value is 92 millisecond in carbonate.Bound water in rocks is not absolute immobile,but related to capillary pressure.We can convert NMR relaxation time distributions directly into capillary pressure curves.The main advantage is that capillary pressure data can be acquired continuously and connected with the wireline logs.However,the conversion is taken with pore space fully saturated with water.The presence of non-wetting hydrocarbon strongly dictates the shape of the T2 distributions and thus invalidates the predicted capillary pressure curve.In this study,we will discuss the methods which are used to convert the NMR logs data into capillary pressure curves and correct the NMR T2 spectra from partial water saturation in rocks.