Porosity and Permeability Heterogeneity in the Upper Wolfcamp,Delaware Basin,West Texas:Implications for Production

摘要

We describe the porosity and permeability of mudrocks and carbonates of the upper Wolfcamp in the Delaware Basin,and infer the impact of these properties on well production.We extracted representative core plugs from each lithology to determine total porosity and permeability.We estimated the total porosity by combining helium porosimetry and nuclear magnetic resonance measurements.We measured liquid(dodecane)permeability using the steady state method at varying confining pressures and interpreted the in-situ permeability.~90% of the pore volume in the stratigraphic section lies within the mudrocks.In both carbonates and mudrocks,the permeability to dodecane(oil)in most of the samples is between 1-50 nD at in situ mean effective stress conditions.The pore system in these low-permeability samples is dominated by nanometer-scale interparticle pores between clays,quartz,and carbonate grains.However,five carbonate samples showed permeabilities between 500-5500 nD;these carbonate samples are rich in dolomite(>10 wt.%).They exhibit a mixed pore system composed of micrometer-scale intraparticle pores within dolomitized microfossils and interparticle pores in the matrix.The high-permeability,dolomite-rich carbonates are thin-bedded(2 to 70 in)and interspersed throughout the stratigraphic section.We constructed a 2D,single phase,layered drainage model where these high-permeability beds are interbedded with the low permeability material.We show that cross-facies flow results in focusing of drainage through the high-permeability layers.This results in an effective permeability of the system that is three times higher than the low-permeability rock that dominates the section.We interpret that permeability heterogeneity plays a critical factor in production.