川中大安寨致密灰岩核磁共振信号分析及储层物性下限分析

NMR signal analysis and lower limit analysis of reservoir physical properties of Daanzhai’s compact limestone in central Sichuan

川中大安寨致密灰岩是我国具有代表性的致密储层,具有物性差、孔隙结构复杂等特点。为了研究该区块储层的特性,本文对15块岩心样品进行核磁共振测试,进而对其进行物性分析。核磁共振技术常用来表征岩石微观孔隙结构和评价储层。实验结果表明,核磁共振T2谱表现为单峰、双峰中左峰占优和近似三峰三种类型,三种类型均表明储层小孔隙发育,并确定了最佳离心力为375psi,T2截止值主要分布在0-4ms。综合孔隙度和渗透率分析表明,川中大安寨地区为纳、微米级孔隙导致储层连通性差,不利于油气的运移,为特低孔、特低渗致密储层。通过经验统计法确定了该区块有效储集层孔隙度下限为0.75%,渗透率下限为0.0035mD,通过根据核磁资料和压汞资料得到的孔隙半径下限值,可得出在进行核磁实验时最佳离心力选择较合适,对二者的平均值0.054μm作为该区块孔隙半径下限值。

Daanzhai compact limestone in central Sichuan is a representative compact reservoir in China which has the characteristics of poor physical property and complex pore structure.In order to study the reservoir characteristics of this block,15 cores were tested by NMR in this paper,and then their physical properties were analyzed.NMR technology is one of the important methods to characterize rock micropore structure and evaluate reservoir.The experimental result shows,the characteristics of T2 spectra of NMR show three types:single peak,double peak,left peak and approximate triple peak.All three types indicate the development of reservoir micropore.The cutoff value of T2 is mainly distributed in 0-4 ms when the optimum centrifugal force is 375 psi.Comprehensive porosity and permeability analysis shows that the reservoir connectivity in Daanzhai area of central Sichuan is poor due to the nanometer and micron pore size.It is not conducive to the migration of oil and gas,and is a tight reservoir with ultra-low poros-ity and permeability.The lower limit of effective reservoir porosity and permeability is 0.75%and 0.0035 m Dis determined by empirical statistics.According to the lower limit of pore radius obtained from NMR data and mercury injection data,it can be concluded that the optimum centrifugal force is suitable for NMR experiments,and the average value of 0.054μm is used as the lower limit of pore radius in this block.