Resolving Differences Between Core and Welltest Permeability in Basal Colorado Sandstones, Canada: The Role of Rock Heterogeneity, Relative Permeability and Formation Damage

Resolving Differences Between Core and Welltest Permeability in Basal Colorado Sandstones, Canada: The Role of Rock Heterogeneity, Relative Permeability and Formation Damage Dan Potocki Dan Potocki PanCanadian Petroleum Limited Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Rocky Mountain Petroleum Technology Conference, Keystone, Colorado, May 2001. Paper Number: SPE-71206-MS https://doi.org/10.2118/71206-MS Published: May 21 2001 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Potocki, Dan. "Resolving Differences Between Core and Welltest Permeability in Basal Colorado Sandstones, Canada: The Role of Rock Heterogeneity, Relative Permeability and Formation Damage." Paper presented at the SPE Rocky Mountain Petroleum Technology Conference, Keystone, Colorado, May 2001. doi: https://doi.org/10.2118/71206-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Rocky Mountain Petroleum Technology Conference / Low Permeability Reservoirs Symposium Search Advanced Search AbstractWelltest permeabilities are about 1 to 3 orders of magnitude lower than average core permeabilities from the same well for gas bearing Cretaceous Basal Colorado channel sandstones in south-eastern Alberta, Canada. The large differences coupled with local anomalously poor production from rock with high core permeabilities have raised uncertainty in both geologic and engineering communities regarding the reliability and representativeness of welltest and core permeabilities, respectively. Differences between core and welltest permeabilities are related to the core analyses, sampling and averaging techniques, and welltest interpretation procedures. Core absolute permeabilities are optimistic in part due to the effects of clay dehydration, rock decompaction, biased oversampling of high permeability intervals, and absence of relative permeability effects. Welltest effective permeabilities have been underestimated for gas wells producing minor amounts of water by wrongly assuming single phase gas flow in permeability calculations. The sum of these features creates the large differences between core and welltest permeability.IntroductionA network of prospective gas charged Basal Colorado fluvial sandstone channels trends roughly northeast-southwest in a region approximately 250 km southeast of the city of Calgary, Canada. The Cretaceous aged Basal Colorado channels in the study area contain gas reserves on the order of 15–20 E6m3 per well and form a significant exploration target.Previous work1 has shown that the Basal Colorado channels in this area unpredictably contain pore-lining smectite clay that causes the sandstone to be easily damaged by fresh water drilling or completion fluids. As the distribution of smectite is not well understood many of the wells have been cored to better characterize reservoir properties. Flow and buildup tests have been performed on seven cored wells after perforation completion to better understand flow capacity and skin. In another cored well, a welltest was performed after a fracture completion. Comparisons of arithmetic averaged core permeability (over the perforated interval) with welltest permeabilities from the eight study wells show that welltest permeabilities are about 1 to 3 orders of magnitude lower than core permeabilities (Fig. 1). Differences between core and welltest permeabilities are anticipated as permeability is dependent on scale, direction and the physical/chemical conditions of the environment in which it is measured. However, differences of almost three orders of magnitude, coupled with local anomalously poor production from rock with high core permeabilities (Fig. 2), have raised uncertainty in both geologic and engineering communities regarding the reliability and representativeness of welltest and core data, respectively.The purpose of this paper is to use the integrated data set obtained from eight wells (cores over perforation intervals, logs, welltests) to illustrate the role that core analyses, rock heterogeneity, core sampling, averaging, relative permeability and welltest analyses have played in causing disparity between average core and welltest permeability.Permeability Terms and DerivationTo facilitate the discussion it is important to review various terms used to describe permeability and the means by which permeabilities are derived. Keywords: relative permeability, average core permeability, rock heterogeneity, formation damage, permeability, core permeability, heterogeneity, sandstone, well 8, welltest permeability Subjects: Reservoir Fluid Dynamics, Formation Evaluation & Management, Flow in porous media This content is only available via PDF. 2001. Society of Petroleum Engineers You can access this article if you purchase or spend a download.

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