基于D-D源的三探头中子孔隙度测井探测响应分析

Response Analysis of Three-Detector Neutron Porosity Logging Based on D-D Source

随着油气勘探进程持续推进,低孔隙度储层越发受到关注,具备更高孔隙度灵敏度的D-D源中子测井存在良好应用前景,为了进一步探索其兼顾中子孔隙度测量灵敏度与化学源测量兼容性的可能性,提出一种基于D-D源的三探头中子孔隙度测井设计并开展分析。为探究D-D源中子孔隙度测量响应特征,利用蒙特卡罗方法,基于三探头测井仪器的基本构成,研究了探测器源距设计,并提出利用测量的近远热中子计数比、中远热中子计数比这2组比值分别表征地层孔隙度,同时对D-D源中子孔隙度测井的地层探测能力与地层测量响应进行了综合分析。研究表明:三探头D-D源中子孔隙度测井仪器探测深度稍浅、纵向分辨率较高;近远热中子计数比值响应表现出更高地层孔隙度灵敏度,低孔隙度地层情况下测得的孔隙度变化效果良好;中远热中子计数比值响应泥岩效应较强,虽无法与化学源测量结果兼容,但在纯岩性及含泥质地层与其较高程度接近。该文研究为D-D源中子孔隙度测井仪器测量应用提供了一定参考。

With the continuous deepening of oil and gas exploration,low porosity reservoirs are receiving more and more attention.D-D neutron logging with higher porosity sensitivity has a good application prospect,a three probe neutron porosity logging based on D-D source is proposed and analyzed for the purpose of exploring its possibility of combining porosity measurement sensitivity and chemical source measurement compatibility.This study aims to explore the response characteristics of D-D source neutron porosity logging.By using Monte Carlo method,a three-detector neutron porosity logging tool's detector spacing is designed and it is proposed to measure thermal neutron near-to-far ratio and middle-to-far ratio to characterize the porosity of the formation,meanwhile,formation detection ability and measurement response of D-D source neutron porosity logging are analyzed.The results show that three-detector neutron porosity logging tool based on D-D source has a slightly shallower detection depth and higher vertical resolution.Thermal neutron near-to-far ratio's response shows good sensitivity to formation porosity and good response in low porosity formation.Thermal neutron middle-to-far ratio's response cannot be compatible with traditional radioactive measurements and its mudstone effect is strong,but it is highly similar to radioactive measurements in conventional lithology and shaly reservoirs.This study provides a reference value for D-D source neutron porosity logging tool application.