D-T_2二维核磁共振脉冲序列改进设计及性能对比

An improved design of D-T_2 2D NMR pulse sequence and performance comparison

针对现有D-T2二维核磁共振脉冲序列无法兼顾扩散系数测量范围和横向弛豫分辨率的难题,在对比PFG(脉冲梯度场)、STE-PFG(stimulated echo PFG)、BP-PFG(Bi-polar PFG)、改良式CPMG(Car-Purcel-Meiboom-Gill)、'扩散编程'、多回波间隔CPMG脉冲序列技术特点的基础上,提出一种基于脉冲梯度场的两窗口、双变量D-T2改进脉冲序列。PFG、改良式CPMG、D-T2改进脉冲序列在气水、油水、稠油模型不同信噪比条件下的正反演数值模拟结果表明,D-T2改进脉冲序列达到了平衡扩散系数测量范围和横向弛豫分辨率的设计要求,在非常规油气储层的探测和测井评价中具有广泛应用前景,可为推动D-T2二维核磁共振技术的发展提供有利条件。

In order to solve the difficulties in D-T22 D NMR technology that cannot balance the dynamic range of the diffusion coefficient measurements and the transverse relaxation resolution in practical applications,an improved design of D-T22 D NMR pulse sequence,based on two ＂ windows＂ and bivariate on pulsed filed gradient,was proposed,after summarizing the technical characteristics of PFG（ pulsed filed gradient）,STE-PFG（ stimulated echo pulsed filed gradient）,BP-PFG（ Bi-polar pulsed filed gradient）,modified CPMG（ Car-Purcel-Meiboom-Gill）, ＂ diffusion editing＂,and multi echo intervals CPMG pulse sequences. The numerical simulation results of different structural models（ gas-water,oil-water and heavy oil-water） under different signal-to-noise ratios show that the modified D-T2 pulse sequence balances the diffusion coefficient measurement range and transverse relaxation resolution successfully. The new pulse sequence has wide applications in the exploration and formation evaluation for unconventional reservoir,and will benefit future development of D-T22 D NMR technology.