Effective Use of Heterogeneity Measures in the Evaluation of a Mature CO2 Flood

摘要

Heterogeneity measures have a long history in the oil and gas industry but have fallen somewhat out of favor in recent years with the advent of more statistically robust characterization tools. Theoretically-based correlations between heterogeneity measures and recoveries at various stages of a waterflood appear to be one of the primary tools in the design and early evaluation of floods when they were initially proposed. Field-wide reports of the heterogeneity measures and their relationship to enhanced recovery response were also reported in the literature, but it is unclear as to whether general correlations were developed or widely used as they were for waterflooding. In this work we evaluate several heterogeneity measures in terms of recovery efficiency and utilization rate in a mature CO2 flood. Core studies available from 41% of the wells in the Little Creek Field, Mississippi were used to compute various heterogeneity measures and the resulting values were correlated with pattern-by-pattern and development area recoveries and CO2 utilization rates at various times over the life of the flood. Weak correlation trends were found for most of the measures when recoveries were evaluated. Slightly stronger correlations were found with utilization rates. Much more significantly, mapping of the well-by-well heterogeneity measures appear to show geological trends better than traditional maps of the basic parameters that make up the measures. These geological trends were then successfully used to adjust rock-types and guide geostatistical modeling of permeability and porosity when performing reservoir modeling and history matching.