Study On The Extraction And Application Of Sensitive Parameters Of T₂ Spectrum Of Nuclear Magnetic Resonance Logging

With the development of the unconventional oil and gas resources,tight continental facies gas reservoirs have become one of the important targets of global exploration.The tight sandstone rocks have complex pore structure and the mineral components,pore space and oil-gas possibility are strongly anisotropic.The nuclear magnetic resonance(NMR)logging could provide much information about the pore structure,physical properties and fluid property.It's a key problem to evaluate the tight sandstone rocks such as pore structure evaluate,reservoir parameters calculate,fluid identification by the NMR logging.Ordos Basin has much low permeability and tight reservoir.Based on the study case of the 7th member of Yanchang formation of the Triassic system in L area,the 9th member of Yanchang formation of the Triassic system in J area et al,the method including the thin section authentication,physical property test,core description,mercury injection experiment,NMR test,rock electrical experiment,NMR logging and formation testing are used to study the tight sandstone rocks about the petrologic feature,physical characteristics,the nuclear magnetic response.And the characteristics of the NMR T2 spectrum and the sensitive parameter are analyzed in different physical properties or pore structure parameters.The pore structure quantitative recognition method,the reservoir parameter calculation method and the fluid identification method are established with the five achievements:(1)After analyzing the NMR T2 spectrums in different physical conditions and pore structures,it's figured out that when the porosity is similar,the NMR T2 spectrum is tend to the right with higher permeability,when the permeability is similar,the NMR T2 spectrum is tend to have higher peak with higher porosity,when the displacement pressure is similar,the NMR T2 spectrum is tend to have higher peak with higher maximum mercury saturation,when the porosity and permeability are similar,the degree of mineralization have little infection on the NMR T2 spectrum.(2)Based on the NMR T2 spectrum characteristics of the tight sandstone and the quantify analyzing of the pore structure information,a series of sensitive parameters are put forward to represent the T2 spectrum,including the T2 spectrum max nonzero time,the T2 spectrum end peak time,the T2 spectrum end peak ordinal,the T2 spectrum end peak value,the T2 spectrum first and end peak time difference,the T2 spectrum first and end peak offset.(3)The NMR test,mercury injection experiment and the physical properties are combined together to represent the pore structure.The rock samples are divided into three categories with the constituted standard.Considering the testing environment difference between the laboratory and the underground,the standard used in the well profile is also established.(4)Based on the T2 spectrum sensitive parameters,the T2 cutoff times are confirmed of different pore structures.The pore and permeability model are established in oil bed.The NMR porosity is corrected by the density log and the T2 spectrum sensitive parameter.The permeability model is established in gas bed.Reservoir parameter results are accord with the core test.(5)To solve the problem about the fluid identification by differential spectrum,considering the NMR transverse relaxation time response regularity of the fluid,the NMR logging and the formation testing,the T2 spectrum sensitive parameter identification plate is established.The identification result is good.The method based on the NMR T2 spectrum sensitive parameter is useful to the pore structure quantitative evaluation,the reservoir parameter calculate,the reservoir effectiveness identification and fluid identification.The method also deepened the NMR logging application in the tight sandstone reservoir evaluation.