一种基于APGD方法的随钻核磁共振测井快速反演算法

A Fast Inversion Algorithm for LWD-NMR Based on APGD Method

中文关键词:  T₂谱反演  加速投影梯度下降算法  现场可编程门阵列  实时计算

英文关键词:T₂ spectral inversion  APGD method  FPGA  real-time computing

中文摘要:

      随钻核磁测井仪器受限于遥传带宽限制和测井时序要求，必须在井下测井仪器中快速实现回波T₂谱反演功能。根据实时性要求并结合原始回波串数据特点，设计一种基于加速投影梯度下降APGD（Accelerated Projected Gradient Descend ）方法的回波T₂谱快速反演算法，充分利用FPGA硬件资源，采用分布式算法将矩阵乘法运算转换为查找表和累加移位操作，并对算法中开方、开根号等运算化简，提高算法执行效率。在自主研发的随钻核磁共振测井仪实验室刻度实验中的运行结果显示，实验结果与理论分析和数值计算相符合，实时性能满足随钻核磁测井仪器快速反演的需求，并且为随钻测井仪器井下数据处理技术领域的研究工作提供了有益的参考。

英文摘要:

      NMR logging tools while drilling is limited by the remote transmission bandwidth limitations and logging timing requirements,so the echo T₂ spectrum inversion function must be quickly implemented in the down hole logging tools.According to real-time requirements and combined with the characteristics of the original echo train data,a fast inversion algorithm for echo T₂ spectrum based on the accelerated projection gradient descent(APGD) method is designed,leveraging FPGA hardware resources,converting matrix multiplication operations into lookup tables and cumulative shift operations by using distributed algorithms,and simplifing the algorithm for operations such as opening square and root sign,improving the efficiency of algorithm execution.The results of the operation in the laboratory scale experiment of the self-developed drilling-following NMR logging instrument show that the experimental results are consistent with the theoretical analysis and numerical calculations,real-time performance meets the needs of fast inversion of the drilling NMR logging instrument,which provides a useful reference for the research work in the field of down hole data processing technology for follow-on logging instruments.