Reservoir heterogeneity is dependent upon depositional environments and subsequent events in the history of the reservoir. From a previous work, we reported variations in poroperms and cementation factor "m" as a function of different scale measurements and emphasized the importance of whole cores in better capturing reservoir heterogeneity. In the present work, we have extended our investigation on the effect of the multi-scale measurements on hundreds of samples from four different wells in a giant carbonate field in Abu Dhabi. Laboratory measurements were conducted on four different scale samples, ranging from full diameter 4 inch whole cores down to 1 inch plug samples. The smaller size samples were taken from the same bigger volume samples for direct comparisons. The multi-scale effect was studied on the variations of reservoir properties including porosity, permeability, capillary pressure and saturation exponent "n". The multi-scale analyses confirmed the variations in rock properties and the influence of heterogeneity on reservoir performance. Whole core porosities tend to be lower than plug porosities. Permeability variations between different sample sizes appear to be governed by the degree of heterogeneity. Different capillary pressure and "n" curves were obtained from whole core and plug samples. The changes in rock properties as a function of sample scale (size) improve the understanding of reservoir heterogeneity and minimize the uncertainty in STOOIP calculations.

Most carbonate reservoirs are commonly characterized by multiple-porosity systems that impart petrophysical heterogeneity to the gross of reservoir interval. Hence, the specific types and relative percentages of pores present, and their distribution within the rocks, exert strong control on the production and stimulation characteristics of carbonate reservoirs.The impact of heterogeneity on core and log measurements is assessed. The challenge is to determine the reliability of relatively small scale properties measured by a log or core to the large scale reservoir property. A related question is one of reconciling the variability seen in high resolution (small volume of investigation) measurements (e.g. core plugs), with the variability in relatively low resolution (large volume of investigation) measurements (e.g. wireline log).Routine and SCAL laboratory measurements on carbonate core samples from prolific reservoir in Abu Dhabi. The measurements were conducted on different scale samples ranging from small trims to full diameter whole core samples. Porosity and permeability obtained from small trims, plugs and whole core samples were compared with log data to study the impact of the measured volume on the results. Electrical property measurements were performed on 1.5" diameter plugs and 4" diameter whole core samples to evaluate the impact of heterogeneity and volume scale on cementation factors which are essential for proper petrophysical interpretation and saturation calculations.Different scale measurements showed variations in both Routine and SCAL data and emphasized the importance of the whole core measurements in representing reservoir heterogeneity which could be used to better evaluate resistivity logs. Plug scale Poroperm data; however, were important in capturing higher degree of reservoir heterogeneity. The better integration between core and log data and the use of the right electrical parameters in petrophysical interpretation tends to minimize the uncertainty in STOIP calculations.

As more and more fields mature in their production life cycle, EOR/IOR methods attain increasing significance. To plan these recovery methods optimally an accurate measure of the remaining hydrocarbon saturation is required to establish if there are sufficient hydrocarbons left in the reservoir to make a recovery process worthwhile. Integrating the state of the art Liquid Trapper coring technique and laboratory analysis on whole core and plugs reduce the uncertainty in this crucial reservoir parameter. New developments in dielectric logging techniques provide accurate remaining saturation answers with depth resolution of the scale of core plugs, for effective comparison and enhanced confidence on the answers. The current study aims to evaluate the remaining oil saturation (ROS) after a water flood in 4 different wells located in a depleted zone of a Cretaceous carbonate reservoir in a giant field, onshore Abu Dhabi. This is the first time a multi-well study involving liquid trapper technique is conducted in the subject field with an objective of better capturing the reservoir heterogeneities and their possible impact on the ROS. Laboratory measurements were conducted on reservoir core samples ranging from full diameter whole cores down to small plugs. The multi-scale analysis confirmed the variations in rock properties and the influence of heterogeneity on the reservoir properties, and ROS distribution. Petrophysical Groups (PG) were also defined and the final ROS values were distributed per PGs. ROS values from cores were compared with the continuous log measurement from the new multi frequency dielectric tool, deployed for the first time in the country. The array sensors of the tool make the borehole correction robust while the dispersion analysis of the multi-frequency data provides saturation answers unaffected by pore fluid salinity and carbonate texture. The uncertainty in ROS measurements and best practices for future is also discussed.

A study was aiming to evaluate the remaining oil saturation (ROS) behind the flood front using Liquid Trapper technology and open hole logs. Four (4) wells were included in this study, two in the South and two in the North of the field. These wells were selected in areas highly flooded by peripheral water injection. The objective is to improve the description of ROS and better estimate the oil recovery efficiency from the field.The Liquid Trapper Coring technique is used to provide more accurate oil saturation data for the reservoir model. It was used in this project in particular to evaluate the remaining oil saturations in the flooded reservoir zones.The Liquid Trapper Coring is a technique to capture any oil that is expelled from the core (due to pressure change) by gas expansion as the core is raised to the surface. This volume of escaping oil can then be calculated over selected intervals and incorporated into the standard saturation analysis performed on the whole core sections. The oil saturation determination from core would give the expected remaining oil where as the oil captured in the trapper barrel would indicate any movable oil in the reservoir.The inner tube of the Liquid Trapper is made of stacked modules, 1m in length and each made up of closed 'cells'. The cells allow capturing of the expelled fluids and segregation of oil, water and gas due to gravity difference. The fluids in the cells surrounding the core are collected to be added to the volume of oil saturation in the core. The volumes were measured in the laboratory by centrifuge and were added to the saturations measured using Dean Stark method.This case study presents the results and uncertainties of using Liquid Trapper Technology in ROS determinations behind flood front of water invaded carbonate reservoir zones. An assessment of this new technique, and its pitfalls in onshore reservoir applications is compared with conventional sponge core coring.