Significance of Selected Set-up Parameters in Return Permeability Measurements Used for Formation Damage Quantification

摘要

Informal visits to formation damage laboratories in Europe and the United States, as well as reviews of literature and discussions with colleagues in other countries have shown that laboratory methods and equipment layout vary significantly from lab to lab. We have noted two important differences related to 1) Core holder design, and here especially core holder position either vertical or horizontal, and 2) Saturation procedures to establish initial water saturations S, either by flooding or by centrifuging. Statoil has during the past 3 years reviewed internal requirements to formation damage laboratory measurements. Within this process, the impact of core holder design and saturation preparations was studied experimentally and by numerical simulation. This paper presents the results of laboratory return permeability measurements and core plug scale simulations systematically performed on - High (<1500 mD) and moderate permeability (<50 mD) outcrop core plug samples - With initial water saturation Swi established by flooding or by centrifuging - Using a 1.56 s.g. [13.0 ppg] high performance water-based mud -A test set-up with variable core holder position: vertical and horizontal. The measurements showed significant differences in return permeability related to the saturation preparations. Core holder position also had a significant impact on the measurements, yet only on those core plugs that were prepared to S_(wi) by flooding. Numerical simulations showed that gravity degradation, in particular in high permeabilities, may affect the distribution of heavy brine based fluid filtrates depending on horizontal or vertical core holder position under otherwise equal capillary pressure conditions. The results of the study helped understanding historical return permeability data produced in different experimental setups. They lead to adjustments of requirements in internal "Best Practice"-type steering documentation and will be offered for presentation and discussion in relevant workgroups within the ISO-system that currently works on revised standards for measurements on reservoir drilling and completion fluids.