Hasan N. Al-Saedi

Coupling of Low-Salinity Water Flooding and Steam Flooding for Sandstone Unconventional Oil Reservoirs

AbstractnIn this study, we combined low-salinity (LS) water and steam as a novel enhanced oil recovery (EOR) method that can provide additional oil recovery up to 63% of original heavy oil in place, which is a very promising percentage. The LS water flooding and steam flooding are two novel combination flooding methods that were combined due to the significant effect of both methods in reducing residual oil saturation (especially heavy oil). The laboratory observations of LS water have been conducted by laboratory and pilot tests, which indicated that LS water could increase recovery to 41% of original oil in place. The thermal aspects provided by steam flooding enhanced heavy oil recovery in many field projects. Although the steam provided additional heavy oil recovery, the density difference between injected steam and in situ heavy oil raised badly behaved displacement issues. The problems could be steam channeling, gravity override, and early breakthrough. In view of that, we developed the low-salinity alternating steam flood (LSASF) to gather the benefits of LS water (altering sandstone wettability), reduce oil viscosity by steam, and prevent the steam problems mentioned earlier. Contact angle measurements showed that flooding the core using LSASF method resulted in more water wetness to the sandstone cores. Many scenarios were conducted experimentally, and the laboratory experiments showed that the optimum setup was reducing the injected LS steam cycles. The shorter the injected cycles are, the more the oil recovery is.n

Sequential injection mode of high-salinity/low-salinity water in sandstone reservoirs: oil recovery and surface reactivity tests

The aim of this paper is to quantify the effect of low-salinity (LS) water on oil recovery from sandstone cores at different temperatures and at various permeabilities, oil viscosities, and Ca2+ concentrations in the formation water. Six sandstone cores were waterflooded with high-salinity (HS) and LS water at various temperatures ranging from 25 to 90xa0°C. Four cores were allocated to oil recovery experiments, and the other two were dedicated to surface reactivity tests. The Swi and Sor of the cores were established, and then the cores were pre-aged for 3xa0days at 70xa0°C with oil in a closed container. We examined the effect of different ionic solutions (HS water, LS water, and double Ca2+ HS water) at different temperatures. The surface reactivity test cores were flooded with the same HS and LS brines that were used in oil recovery forced-imbibition experiments. During flooding, samples of the effluent were analyzed for pH and Ca2+. The absence of an oil phase enabled us to isolate and quantify the important water–rock reactions. Ca2+ desorption from the core that was aged in the double Ca2+ concentration was larger than that desorbed from the other core, but pH and pressure was less than the other core during surface reactivity tests. Due to dehydration at high temperatures, the desorption of Ca2+ decreased as the temperature increased. Also, as the temperature increased, the pH gradient between the HS and LS water effluents decreased. Oil recovery forced-imbibition experiments with a double Ca2+ concentration showed a small LS water effect at all temperatures, meaning that the cores became more water-wet; however, the LS water effect was much greater when the amount of Ca2+ in the HS water was decreased by half. Furthermore, as the core permeability and oil viscosity increased, our tests showed a greater positive effect from the LS water. This work attempts to isolate the separate effects and thus examines the oil recovery achieved with the most important LS waterflood factors, which are temperature, ion exchange, and pH.

Eliminate the role of clay in sandstone: EOR low salinity water flooding

Low-salinity (LS) water flooding mechanism enhanced oil recovery (EOR) method in sandstone has been extensively debated in the literature. Many mechanisms have been proposed, but these proposed mechanisms remain a topic of debate. In this study, we propose to quantify control of mineral composition and water chemistry on water/rock interactions and wettability change during low-salinity waterflooding of spatially heterogeneous sandstone porous media. We intended to identify the dominant process of wettability alteration through considering water–rock interaction mechanisms containing/non-containing clays. Water chemistry partially determines the dominant wettability alteration. This includes salinity, type of ions, and possibly pH. Sandstone core and free clay sand core were prepared in chromatography columns and were water flooded with high/low/high-salinity water at different temperatures. Brine with high salinity 100,000xa0ppm was injected to simulate formation water, then, inflow low-salinity water 1100xa0ppm at different temperatures. Concentrations of Ca2+ and CH3COO− and pH were recorded. The core contains quartz only, to investigate the role of clay in the mechanism of smart water EOR. The results proved that during flooding the free clay core by low-salinity water the carboxylic acid detached from the sand, albeit not as great as that of the clay-containing cores. On the other hand, ICP-OES showed a noteworthy desorption of Ca2+ from the free clay core surface. That indicates further RCOO− recovery in the absence of clay. It has been observed that during flooding by LS water, the pH increased significantly. Also, as the temperature increased the pH of the LS water decreased and amount of Ca2+ decreased in the effluent. This work presents the results of forced imbibition experiments to examine the effect of clay in sandstone during LS flooding EOR.

Comparison Between Cold/Hot Smart Water Flooding in Sandstone Reservoirs

The incremental oil recovery has been investigated and approved by many laboratory and field projects using water flooding in tertiary stage. The salinity of the injected water is an important factor observed by many researchers. The more salinity decreases the more oil recovery obtained. The investigations on the hot low salinity water flooding have been conducted by many researchers and they found out that it is useful for increasing oil recovery especially heavy oil due to reducing oil viscosity and make it easy to produce to the surface. The thermal expansion of water plays an important role in the incremental oil recovery mechanism, reducing the density of the injected water relative to the aquifer water. This reduces mixing; minimizing thermal loses to the aquifer. Hot water flooding may also increase the economic life of individual wells by as much as a factor of two. Smart water was also used to alter the reservoir wettability and increase oil recovery by manipulating the divalent cations in the injected water. In this study, we used hot and cold smart water and injected both into the sandstone saturated with crude oil in order to investigate the important role of smart water itself and hot smart water. The systematic results showed that changing some cations in the injected brines was better than to spend more money to heat the smart water. The divalent cations Ca2+ and Mg2+ were the most effective component in the smart water. In this study, we also studied the pH effect of the cold/hot smart water effluent smart water EOR.