Characters and Petrophysical Evaluations of Different Super-Permeability Zones in the Cretaceous Bioclastic Limestone Reservoirs-A Case Study of AA Field,Iraq

摘要

Super-permeability zones(SPZs)commonly exist in the bioclastic limestone reservoirs in the Middle East.The existence of SPZs lead to strong heterogeneity and further cause some severe issues during the following reservoir development.It is the specific characteristics of SPZs,such as low net pay,weak logging response,and different geneses,that challenge its quantitative characterization by log data.This paper firstly focuses on the property studies of 3 different SPZs based on full core photo and core sample photo observation,porosity and permeability,mercury injection capillary pressure,cast thin section,and NMR T2 spectrum,which are mainly distributed in Kh2-2,Ru2a-2,and Ru3.Then the identification criteria of SPZs are established through log responses including conventional and special(XRM1)wire-line logs.Next,petrophysical parameters are interpreted quantitatively for SPZs,and the vertical as well as planar distributions of 3 types of SPZs have been obtained from the above log interpretation results.The results indicate that:(1)The lithology/rock types of SPZs in Kh2-1-2L are the mixture of microsparite bioclastic packstone(light gray patch color)and intraclastic grainstone(dark color),the Ru2a-2 is mainly homogeneous micrite bivalve calcarenite,while the Ru3 is sparry arene bivalve limestone with medium heterogeneity.Further analysis for the rock types in Kh2-1-2L indicates that intraclastic grainstone parts show higher porosity and permeability based on visual observation of core photos and core cast thin section,while microsparite bioclastic packstone parts have no oil show and develop fractures in small scale and small vuggies from limited corrosion;(2)There is fair linear relationship between core permeability and porosity for SPZs in Ru2a-2,poor linear relationships for those in Ru3,whereas nearly negative correlation for the ones in Kh2-1-2L,which is mainly caused by complicated lithology/rock types and pore space system;(3)In planar,SPZs distribute of Kh2-1-2L in overall field,and the thickness becomes thinner from AD1,AD2 to AD4 blocks gradually;whereas SPZs in Ru2a-2 mainly and continuously develop in higher and south-east local areas of AD1 block and become thicker towards the southeast direction,and SPZs in Ru3 mainly develop and continuously distribute in higher local areas of AD1 block.These results provide an effective technical support for the water-flood development strategy.