Abdulrahman A. AlQuraishi

Efficiency of enhanced oil recovery using polymer-augmented low salinity flooding

Abstract Oil recovery from heavy oil resources has always been a challenging task. This work is aimed at investigating the recovery efficiency of polymer-augmented low salinity waterflooding in heavy oil reservoirs. The main recovery mechanism behind low salinity waterflooding is wettability alteration to more water-wet state. On the other hand, polymer flooding is performed to control fluids mobility and hence improve displacement efficiency. Combining both recovery methods is expected to add to recovery efficiency obtained by individual methods, and the aim of this work is to explore this experimentally. In this study, several laboratory experiments were conducted using Berea and Bentheimer sandstone cores starting with base runs of continuous secondary seawater and tertiary twice and 10 times diluted seawaterflooding (low salinity). Significant incremental oil recovery was obtained when flooded with low salinity water, and 10 times diluted seawater was determined to be used as low salinity water. Contact angle and Zeta potential measurements indicate wettability alteration due to clay detachment as the main recovery mechanism. Synergy of water secondary flooding and polymer tertiary flooding at different water salinity levels proved the efficiency of hybrid low salinity polymer flooding process in Berea sandstone. Low water salinity during secondary injection mode played a major role on ultimate recovery with less contribution to tertiary polymer slug injection. High salinity waterflooding provided lower secondary recovery leaving more residual oil for polymer slug to act on at that cycle. Smaller polymer slug of 0.1 pore volume was found to be sufficient in tertiary flooding with low salinity water but with slightly slower recovery rate. Bentheimer sandstones known for its low clay content were subjected to polymer-augmented waterflooding at high and low salinity levels. Close secondary and tertiary recoveries were obtained for the two salinity levels with slower recovery rate for low salinity run. Minute clay content and water-wet characteristic as determined by contact angle measurements may explain the lack of water salinity effect on recovery. The lack of salinity role and the two shock fronts with connate water bank in between known to exist during low salinity flooding may explain the slower recovery rate encountered. Comparison of both sandstones indicates that less ultimate recovery from Berea rocks, and this can be attributed to their initial intermediate wet state in contrast to the water-wet Bentheimer sandstone rocks.

Effect of triaxial in situ stresses and heterogeneities on absolute permeability of laminated rocks

This work aims at improving our understanding of the effect of triaxial stress on absolute permeability of homogeneous and heterogeneous rocks. Measurements of absolute permeabilities of homogenous and heterogeneous laminated rock samples under hydrostatic and different laboratory-simulated triaxial in situ stress loadings were prepared. Experiments were conducted using homogenous, standard Berea and heterogeneous laminated sandstone cores (with lamination parallel to the flow direction). The effect of in situ stress variation on absolute permeability was investigated. Absolute permeability of homogenous sandstones sample decreased in a uniform manner as the axial load increased below the ultimate shear strength. As axial stress exceeds the radial confining stress, slight increase attributed to microcracks opening was noticed. For laminated sandstones, the scenario is quite different. Permeability shows exactly a similar trend of permeability drop as axial load increases due to inferred matrix compaction. At certain axial load, the permeability starts to increase due to inferred dilatancy of microcracks at the lamina faces and then drops again as axial load increases due to lamina compaction. If the axial load is further increased, pore collapses and grain-to-grain cementing breaks down into pore space followed by microcracks development predominantly parallel to the axial load leading to permeability enhancement. It has been concluded that absolute permeability changes due to lamination opening and closure as a result of loading magnitude and orientation. It is also concluded that permeability of the formation rock is affected by heterogeneity depending on the direction of lamination as well as the state of the stresses applied and loading type.

New correlations for prediction of saturated and undersaturated oil viscosity of Arabian oil fields

New correlations for saturated and undersaturated oil viscosity were developed for Saudi Arabian crude oil. The data consist of 79 and 71 experimental measurements of saturated and undersaturated crude oil viscosity, respectively, at reservoir conditions. Other PVT measurements above and below bubble point pressure are also included. The new correlations were developed using genetic programming approach. The new models were developed and tested using linear genetic programming (GP) technique. The models efficiency was compared to existing correlations. Average absolute relative deviation, coefficient of correlation, and crossplots were used to evaluate the proposed models, and their outputs indicate the accuracy of the GP technique and the superiority of the developed models in comparison with the commonly utilized models tested.

A simple apparatus to study the effect of lithology, permeability, and wettability on spontaneous imbibition

The spontaneous imbibition phenomenon is an important process in hydrocarbon recovery. Laboratory study of imbibition is affected by many parameters including, rock characteristics, boundary conditions, length of the sample, variable interfacial tension, and sample heterogeneity. Investigating spontaneous imbibition enhances our understanding of the imbibition mechanism and, hence, helps improve waterflooding used in the oil industry. A simple apparatus has been developed to resemble naturally fractured reservoirs. Using the developed apparatus, the effects of lithology, permeability, and wettability on spontaneous imbibition have been experimentally investigated. Some encountered unexpected technical problems during the experiments are overcome and reported in this paper. Details of the developed apparatus are shown and spontaneous imbibition results are presented. First, the effect of permeability on the oil recovery rate is presented. In addition, obtained curves of oil recovery by water spontaneous imbibition using different lithology are presented. Finally, results of oil recovery from Berea sandstone core sample before and after wettability alteration are shown.