摘要
提出了一种可以提高核磁共振测井测量速度的新型测量脉冲序列 ,它基于对原有CPMG测量脉冲序列的改进 .在原有的测量序列中 ,在一个CPMG脉冲序列结束之后 ,直接进行等待 (T1延时 ) ,以使磁化强度矢量能够完全恢复到平衡位置 ,然后再进行下一个CPMG脉冲序列的测量 .由于测井仪器的连续运动 ,在测量含有长T1成分的地层时 ,等待时间需要取得较长 ,使得测井速度很低 .但在实际地层中 ,恰恰又是油气的T1较长 ,这无疑给核磁共振测井带来了麻烦 .作者发现 ,如果在一个CPMG脉冲序列结束之后在 -x方向先施加一个 90°脉冲 (或在x方向施加一个 2 70°脉冲 ) ,再进行等待 ,就能更好地使长T1成分得到极化 ,从而缩短等待时间、提高测量速度 .文中对这种改进后的脉冲序列进行了计算和分析 ,证明它确实具有一定的优越性 .
A new pulse sequence for the measurement of NMR logging is proposed in this article, based on the improvement of original CPMG pulse sequence. In the orig inal pulse sequence, after a CPMG pulse sequence, wait time (or T\-1 relay) is needed to allow the magnetization vector return to equilibrium, then the ne xt me asuring CPMG pulse sequence can be applied. The wait time is kept long and the l ogging speed is low in formations that contain long T\-1 components, since t he log ging apparatus is moving continuously along the bore hole. This is unfavorable b ecause the spin-latti ce relaxation time (T\-1) of oil and gas is always long . However, it's noti ced th at if a 90° pulse from the -x direction (or a 270° pulse from the x direction ) i s applied after the former CMPG pulse sequence, the long T\-1 components can be po larized more completely, then the wait time can be shortened and logging speed c an be improved. The advantage of the improved pulse sequence is proved by calcul ations and analyses.
出处
《波谱学杂志》
CAS
CSCD
北大核心
2000年第3期177-182,共6页
Chinese Journal of Magnetic Resonance
基金
ProjectsupportedbyNationalNaturalScienceFoundationofChina(No .599770 2 3 )
