Laboratory Investigation of the Impact of Injection-Water Salinity and Ionic Content on Oil Recovery From Carbonate Reservoirs

This paper described a core flooding laboratory study conducted using composite rock samples from a carbonate reservoir. The aim of the study was to investigate the impact of salinity and ionic composition on oil, brine and rock interactions. Experimental parameters and procedures were designed to replicate reservoir conditions and current field injection practices. Results of the study demonstrated that alterations in the salinity and ionic composition of injected water can have a significant impact on the wettability of the rock surface. Nuclear magnetic resonance (NMR) studies confirmed that injecting different salinity slugs of seawater in carbonate core samples can cause a significant alteration in the surface charges of the rock, and lead to increased interactions with water molecules. The constant reduction of pressure drop across the composite cores with the injection of different diluted versions of water also provided proof of brine, oil and rock alterations. Results of the study indicated that the driving mechanism for waterflooding recovery processes is wettability alteration, which can be triggered by alterations in carbonate rock surface charges, and improvements in the connectivity between rock pore systems that coexist in carbonate rock samples. 41 refs., 8 tabs., 16 figs.

Laboratory Investigation of Novel Oil Recovery Method for Carbonate Reservoirs

Improved/Enhanced Oil Recovery from Carbonate Reservoirs by Tuning Injection Water Salinity and Ionic Content

Laboratory measurement of low permeability unconventional gas reservoir rocks: A review of experimental methods

Wettability alteration with brine composition in high temperature carbonate reservoirs

Understanding Waterflood Residual Oil Saturation of Four Carbonate Rock Types

In this paper, the authors construct a novel, state-of-the-art laboratory setup that captures several hundred pressure readings per second to study the response of cores to pressure disturbances. The authors used their new experimental setup to measure accurately and rapidly permeability of homogeneous cores, matrix and fractured properties of a fractured rock, and the individual segment properties of a butted core sample.

Characterization of Core Scale Heterogeneities Using Laboratory Pressure Transients

Method and apparatus for determining heterogeneous properties of a core sample by use of pressure transients. In the method, a pressure is applied to a first closed vessel at one end of a core sample. The pressure is then allowed to dissipate into the core and into a second closed vessel at the other end of the core sample. The pressure in at least one of the vessels or the core itself is measured and recorded as a function of time during the pressure dissipation. The volume of the first vessel is then varied and pressure is once again applied to the first vessel and allowed to dissipate into the core and second vessel. The pressure is again measured and recorded as a function of time during the pressure dissipation. The two sets of recorded measurements are then analyzed to detect deviations from theoretical responses in homogeneous cores which identify heterogeneities. Preferably, the volume of the first vessel has in either the first or second test a volume sufficiently small to cause a measurable variance between an actual pressure transient response for the system and a theoretical pressure transient response for the system. By using a small volume in both tests and reversing the direction of the second test, different heterogeneous properties may be detected.

Method and apparatus for rock property determination using pressure transient techniques and variable volume vessels

Laboratory determination of residual oil saturation (ROS) in carbonate cores is sometimes uncertain due to wide pore size distribution, core scale heterogeneity, and complex wettability. The values obtained in laboratory tests may vary depending on flow rates, the type of samples (plugs or whole cores), and sample preparation techniques. The purpose of our study is to integrate modern flow visualization technology with conventional laboratory tools to provide a comprehensive picture of waterflood recovery behavior in four carbonate cores. Our data set comprise thin sections; mercury injection; 3-D porosity distribution; oilfloods and waterfloods on cleaned samples; and 3-D flow imaging of miscible floods, oilfloods, and waterfloods on restored state samples. The 3-D Computed Tomography (CT) images allowed us to understand the reasons for decrease in oil saturation observed with increased pressure drop in the corefloods; whether this is due to capillary-end effects, core scale heterogeneity, or actual reduction in ROS. We find that ROS values under field-rate flooding conditions (~ 1 psi/foot, Nc • ~ 10 -8 , lateral flood) are in the 30%-60% PV range. These ROS values reduce significantly as the pressure gradient applied during the floods is raised from field values to the much higherpressure gradients sometimes used in laboratory testing (~ 100 psi/ft, Nc ~ 10 -6 ). The carbonate samples with large pore-throat aspect ratios have the largest ROS values and the biggest variation with the pressure drop used in the waterfloods.

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Laboratory evaluation of waterflood residual oil saturation in four carbonate cores

This study reports injectivity data for the different flow zones present during a Water-Alternating-Gas (WAG) flood. The experiments were carried out on four rock types sampled from the Grayburg dolomite formation in West Texas. We used liquid CO 2 -water, toluene-liquid CO 2 -water and crude oil-liquid CO 2 -water systems to isolate mechanisms and to address wettability concerns. We found that the injectivity of the chase water zone was comparable to the initial waterflood injectivity, and increased as the trapped CO 2 dissolved. The injectivity of the CO 2 -rich zone was significantly higher than the initial waterflood injectivity. Ambient condition toluene tests and reservoir condition crude tests gave similar results for the water and CO 2 zones. However the crude oil, even prior to any CO 2 injection, exhibited a strong tendency to plug the core samples. We were unable to restore permeability in the plugged up core samples by continuous flushing of different solvents.

Frank Nakagawa

Papers

Understanding Waterflood Residual Oil Saturation of Four Carbonate Rock Types

Characterization of Core Scale Heterogeneities Using Laboratory Pressure Transients

Method and apparatus for rock property determination using pressure transient techniques and variable volume vessels

Laboratory evaluation of waterflood residual oil saturation in four carbonate cores

Laboratory Investigation of Injectivity Losses During WAG in West Texas Dolomites