Abstract This paper presents error analysis and applications of a new method for estimating permeability from logs. This method is called PermLog and its development is documented by Semmelbeck et al. We present an example application of PermLog and show how it can be used with pressure transient testing to characterize complex, low to moderate permeability gas reservoirs. We also present the results of a detailed error analysis in which we determine the expected accuracy of the PermLog permeability estimates. We show confidence intervals expected from PermLog based on assumed accuracy of parameters used in the PermLog analysis.
Well tests in complex multilayered reservoirs can be analyzed with more realistic reservoir models when layer permeability estimates are provided by the PermLog analysis. Monte-Carlo error analysis indicates that at least 80% of permeability estimates from PermLog will be within a factor of 3 of the true in-situ gas permeability when the permeability is in the range of 0.01 to 10 md.
The permeability estimates fine-tuned by matching pressure transient behavior will lead to better performance forecasts and optimization of stimulation treatments and well spacing.
Introduction Many reservoirs are composed of multiple layers with unequal permeability. Detection of these layers and evaluation of their productive characteristics early in the life of the reservoir is critical for sound reservoir management. Conventional well testing provides a single "effective permeability" for the entire tested zone. The effective permeability is strongly influenced by the presence of low-volume, high-permeability lenses or streaks that contribute significantly to early-time production but deplete rapidly and do not contain a significant portion of the reserves. This problem is particularly troublesome in the thick, low to moderate permeability gas reservoirs in the Gulf Coast region of the United Sates. These reservoirs often contain laterally extensive shale streaks which lower vertical permeability and reduce the amount of crossflow between high and low permeability layers.