Shaun Ireland

Coreflooding studies to investigate the potential of carbonated water injection as an injection strategy for improved oil recovery and CO2 storage

Carbonated water injection (CWI) is a CO2-augmented water injection strategy that leads to increased oil recovery with added advantage of safe storage of CO2 in oil reservoirs. In CWI, CO2 is used efficiently (compared to conventional CO2 injection) and hence it is particularly attractive for reservoirs with limited access to large quantities of CO2, e.g. offshore reservoirs or reservoirs far from large sources of CO2. We present the results of a series of CWI coreflood experiments using water-wet and mixed-wet Clashach sandstone cores and a reservoir core with light oil (n-decane), refined viscous oil and a stock-tank crude oil. The experiments were carried out to assess the performance of CWI and to quantify the level of additional oil recovery and CO2 storage under various experimental conditions. We show that the ultimate oil recovery by CWI is higher than the conventional water flooding in both secondary and tertiary recovery methods. Oil swelling as a result of CO2 diffusion into the oil and the subsequent oil viscosity reduction and coalescence of the isolated oil ganglia are amongst the main mechanisms of oil recovery by CWI that were observed through the visualisation experiments in high-pressure glass micromodels. There was also evidence of a change in the rock wettability that could also influence the oil recovery. The coreflood test results also reveal that the CWI performance is influenced by oil viscosity, core wettability and the brine salinity. Higher oil recovery was obtained with the mixed-wet core than the water-wet core, with light oil than with the viscous oil and low salinity carbonated brine than high-salinity carbonated brine. At the end of the flooding period, an encouraging amount of the injected CO2 was stored in the brine and the remaining oil in the form of stable dissolved CO2. The experimental results clearly demonstrate the potential of CWI for improving oil recovery as compared with the conventional water flooding (secondary recovery) or as a water-based EOR (enhanced oil recovery) method for watered out reservoirs.

Direct observation of CO2 transport and oil displacement mechanisms in CO2/water/oil systems

As the concern over the greenhouse gas effects of carbon dioxide (CO2) increases, its injection into oil and gas reservoirs for enhancing hydrocarbon recovery and in saline aquifers for storage is on the rise. Variation of reservoir pressure and temperature affects the properties of CO2 and its interaction with reservoirs resident phases. Although in most cases CO2 would be in supercritical state at reservoir conditions, however, it is necessary to understand the flow and displacement mechanisms of CO2/water/ oil systems in porous media under various reservoir conditions.

Novel Insights Into Mechanisms of Oil Recovery by Use of Low-Salinity-Water Injection

The underlying mechanism of oil recovery by low salinity water injection (LSWI) is still unknown. It would, therefore, be difficult to predict the performance of reservoirs under LSWI. A number of mechanisms have been proposed in the literature but these are controversial and have largely ignored crucial fluid/fluid interactions. Our direct flow visualization investigations have revealed that a physical phenomenon takes place when certain crude oils are contacted by low salinity water leading to a spontaneous formation of micelles which can be seen in the form of micro-dispersions in the oil phase. In this paper, we present the results of a comprehensive study that includes experiments at different scales designed to systematically investigate the role of the observed crude oil/brine interaction and micelle formation in the process of oil recovery by LSWI. The experiments include; direct flow (micromodel) visualization, crude oil characterization, coreflooding, and spontaneous imbibition experiments. We establish a clear link between the formation of these micelles, the natural surface active components of crude oil, and the improvement in oil recovery due to LSWI. We present the results of a series of spontaneous and forced imbibition experiments carefully designed using reservoir cores to investigate the role of the micro-dispersions in wettability alteration and oil recovery. To further assess the significance of this mechanism, in a separate exercise, we eliminate the effect of clay by performing a LSWI experiment in a clay-free core. Absence of clay minerals is expected to significantly reduce the influence of the previously proposed mechanisms for oil recovery by LSWI. Nevertheless, we observe significant additional oil recovery compared to high salinity water injection in the clay-free porous medium. The additional oil recovery is attributed to the formation of micelles stemming from the crude oil/brine interaction mechanism described in this work and our previous related publications. Compositional analyses of the oil produced during this coreflood experiment indicates that the natural surface active compounds of the crude oil had been desorbed from the rock surfaces during the LSWI period of the experiment when the additional oil was produced. The results of this study present new insights into the fundamental mechanisms involved in oil recovery by LSWI and new criteria for evaluating the potential of LSWI for application in oil reservoirs. The fluid/fluid interactions revealed in this research applies to oil recovery from both sandstone and carbonate oil reservoirs.

Relative Permeabilities at Near-miscible Conditions - Effects of Connate Water Saturation, Wettability, Hysteresis and Permeability

We present a series of two-phase (oil and gas) drainage and imbibition relative permeability (kr) curves at near-miscible (IFT=0.04 mN/m) conditions. An equilibrium mixture of methane/n-Butane at 38°C and 1840 psia was used as the oil and gas in the unsteady-state coreflood experiments which were carried out to obtain the kr curves. A high-permeability (1000 mD) and a lower permeability (65 mD) cores were used in the experiments and both water-wet and mixed-wet wettability conditions were examined. The results show that the present of immobile water saturation in water-wet cores could improve oil relative permeabilities and reduce gas relative permeabilities in both imbibition and drainage directions. The results show that despite a very low gas-oil IFT, there is still significant hysteresis between imbibition and drainage cycles for both the oil and gas relative permeabilities in the 65md core. The results help us better understand the impacts of some of the important parameters of multiphase flow through porous media on kr curves and their hysteresis especially in low IFT gas-oil systems and mixed-wet rocks. Obtaining accurate kr and kr hysteresis is extremely important for predicting the performance of gas injection in oil reservoirs.