An experimental investigation of smart-water wettability alteration in carbonate rocks – oil recovery and temperature effects (original) (raw)
Related papers
Journal of Petroleum Exploration and Production Technology, 2019
Smart water flooding as a developing technique utilizes modified water chemistry in terms of salinity and composition to prepare the best-suited brine composition for a specific brine/oil/rock system to obtain higher oil recovery efficiency. Huge amount of unrecovered oil is expected to be remained in carbonate reservoirs; however, few research works on incremental oil recovery during smart water injection in carbonate cores at reservoir condition are reported. Several core flooding tests using one of the Iranian carbonate reservoir rock are conducted to check the effectiveness of smart water injection for more oil recovery efficiency. The results reaffirm the positive effect of sulfate ions to play a key role for better smart water performance. Moreover, it was concluded that the calcium ion concentration is not as effective as magnesium ion for the tests performed at reservoir condition. Synthetic sea water (high-salinity) flooding was considered as the base scenario which results in almost 63% oil recovery efficiency for secondary recovery scenario. Formation of micro-emulsions was found to be the main reason of additional pressure drop during low-salinity water flooding. This clearly showed that the diluted smart water injecting increases the ultimate oil recovery up to 4-12% for already water-flooded carbonate reservoirs.
Time-Dependent Physicochemical Changes of Carbonate Surfaces from SmartWater (Diluted Seawater) Flooding Processes for Improved Oil Recovery, 2018
Over the past few decades, field-and laboratory-scale studies have shown enhancements in oil recovery when reservoirs, which contain high-salinity formation water (FW), are waterflooded with modified-salinity salt water (widely referred to as the low-salinity, dilution, or SmartWater effect for improved oil recovery). In this study, we investigated the time dependence of the physicochemical processes that occur during diluted seawater (i.e., SmartWater) waterflooding processes of specific relevance to carbonate oil reservoirs. We measured the changes to oil/water/rock wettability, surface roughness, and surface chemical composition during SmartWater flooding using 10-fold-diluted seawater under mimicked oil reservoir conditions with calcite and carbonate reservoir rocks. Distinct effects due to SmartWater flooding were observed and found to occur on two different timescales: (1) a rapid (<15 min) increase in the colloidal electrostatic double-layer repulsion between the rock and oil across the SmartWater, leading to a decreased oil/ water/rock adhesion energy and thus increased water wetness and (2) slower (>12 h to complete) physicochemical changes of the calcite and carbonate reservoir rock surfaces, including surface roughening via the dissolution of rock and the reprecipitation of dissolved carbonate species after exchanging key ions (Ca 2+ , Mg 2+ , CO 3 2− , and SO 4 2− in carbonates) with those in the flooding SmartWater. Our experiments using crude oil from a carbonate reservoir reveal that these reservoir rock surfaces are covered with organic−ionic preadsorbed films (ad-layers), which the SmartWater removes (detaches) as flakes. Removal of the organic−ionic ad-layers by SmartWater flooding enhances oil release from the surfaces, which was found to be critical to increasing the water wetness and significantly improving oil removal from carbonates. Additionally, the increase in water wetness is further enhanced by roughening of the rock surfaces, which decreases the effective contact (interaction) area between the oil and rock interfaces. Furthermore, we found that the rate of these slower physicochemical changes to the carbonate rock surfaces increases with increasing temperature (at least up to an experimental temperature of 75 °C). Our results suggest that the effectiveness of improved oil recovery from SmartWater flooding depends strongly on the formation of the organic−ionic ad-layers. In oil reservoirs where the ad-layer is fully developed and robust, injecting SmartWater would lead to significant removal of the ad-layer and improved oil recovery.
Wettability and oil recovery from carbonates: Effects of temperature and potential determining ions
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2006
The success of oil recovery from fractured low permeable carbonates by water injection is dictated by the wetting properties of the rock surface. Potential determining ions like Ca 2+ and SO 4 2− have influence on the surface charge of the carbonate rock and are thereby linked to its wetting properties. In the present study, zeta potentials of chalk surfaces were measured by changing the sulfate and calcium concentrations in aqueous chalk suspensions. Series of long-term spontaneous imbibition tests were conducted at 70, 100 and 130 • C using oil containing chalk cores which were close to neutral wetting conditions. The concentration of SO 4 2− in the imbibing fluids varied above and below the seawater concentration, while the Ca 2+ concentration was kept constant. Sulfate acted as a wettability modifying agent by improving the water wetting nature of the chalk. The major experimental observations were: (1) the zeta potential on chalk was determined by the relative concentration of Ca 2+ and SO 4 2− present.
Impact of Multi-ion Interactions on Oil Mobilization by Smart Waterflooding in Carbonate Reservoirs
Journal of Petroleum & Environmental Biotechnology, 2016
The injected brine composition has been observed to have intense effect on efficiency of waterflooding in carbonate reservoirs. This process is known as smart waterflooding and has proved to be an effective process in improving oil recovery. Different approaches have been tested in carbonate reservoirs due to the complexity of the process. Based on these approaches, different mechanisms have been proposed with some level of uncertainties. This has led to several arguments on the chemical mechanisms responsible for such feat achieved. One of the approaches is discussed in this paper, however with much interpretation considering all factors influencing the oil-brine-rock interactions. Therefore, this paper presents the influence of multi-ion interactions during smart water flood on carbonates. Sequential flooding of formation brine and smart brines and the effluent ion analysis were conducted to confirm the multi-ion interactions leading to improved recovery. In addition, zeta potential measurement was conducted to examine the alteration process and correlated with the core flood results. The results from zeta potential measurement showed that multi-ion interaction alters the rock surface charge, which led to more water-wetness. Significant improvement in oil displacement efficiency was observed beyond the secondary waterflood and effluent ionic analysis demonstrated that these multi-ionic interactions led to the observed alteration.
Journal of Molecular Liquids, 2017
As the demand for crude oil increases, the oil-producing countries try to increase production. Enhanced Oil Recovery (EOR) techniques play a significant role in improving oil production. Improved or smart water injection, among the methods, has higher performance due to its low cost. Carbonated smart water is injected to improve smart water capabilities. Dissolution of carbon dioxide in water will change chemical properties of the injected water to facilitate wettability alteration from hydrophobic to hydrophilic more effectively. Besides, it causes swelling and changes of oil density and viscosity by transferring from the aqueous phase to the oil phase. Adding CO 2 to the smart solution can have other effects, expressed as dissolution and carbonate rock weight alteration, in addition to the wettability alteration on carbonate rock. In this communication, NaCl, KCl, Kl, MgCl 2 , CaCl 2 , Na 2 SO 4 , MgSO 4 , and K 2 SO 4 were used to produce smart water, and CO 2 gas was utilized to carbonate the water. Observational/visual and contact angle tests were then carried out to express wettability alteration of carbonate rock with smart water and carbonated smart water. These observational tests clearly indicate the wettability alteration property of injected materials. Carbonated smart water exposed to rock analysis shows that Mg 2+ ion was higher in comparison with Ca 2+ rate in tested carbonate rock. Therefore, we can say that the rock is a Dolomite one. Finally, by conducting tests on oil production imbibitions, we show that the smart water while utilizing the provided mechanism is capable of improving the oil production in contrast to imbibitions with normal water, such that the imbibitions with smart water increases the production 33% more in contrast to production with initial formation water.
Fuel, 2019
Imbibition is one of main production mechanisms in fractured carbonate reservoirs. This mechanism is very dependent on hydrophilicity of reservoir rock and somehow is controlled by it. The contact angle tests, due to the test conditions, i.e, a polished rock section-crude oil droplet system, do not easily indicate the wettability of the porous medium but generally, are accepted to expression of rock wettability. Imbibition tests with a strong dependence on wettability can generalize contact angle tests to wettability of porous medium. Carbonated smart water injection can active water imbibition mechanism and increase production in fractured carbonate reservoirs by wettability alteration to hydrophilic. In this study, the optimal concentration of saline water used with oil in Karanj and Gachsaran reservoirs in Iran was determined by calculating the contact angle in different concentrations and dilutions. Then, the optimal solutions were carbonated by adding carbon dioxide at various temperatures and pressures. The effect of carbon dioxide on wettability of pre-hydrophobized sections was investigated by contact angle experiments. The results show the efficiency of carbonated smart water in wettability alteration as compared with smart water. Then, oil-saturated carbonate plugs were exposed to spontaneous imbibition by optimal solutions in the
Wettability alteration and improved oil recovery in unconventional resources
Journal of Petroleum Science and Engineering, 2022
Carbonate wettability is dictated by the surface chemistry related to stability of the water film between the oil phase and the rock surface. It has been verified, both in the field and laboratory, that seawater is an excellent injection fluid to enhance the oil recovery from fractured chalk. The objective of different papers in this series has been to understand the chemistry for improved spontaneous imbibition of seawater into low permeable chalk at low water wetness. Improved spontaneous imbibition of water will take place if the chalk becomes more water-wet during the production phase. The potential determining ions present in seawater, Ca 2+ and SO 4 2− , have great influence on the surface charge of chalk, which can modify the wettability during water injection. In the present study, it was verified that Mg 2+ is another strong potential determining ion towards chalk, which can increase the positive surface charge density. At high temperatures, Mg 2+ can even substitute Ca 2+ from the chalk surface, and the degree of substitution increased as the temperature increased. The interplay between the three potential determining ions: Ca 2+ , Mg 2+ and SO 4 2− and the chalk surface with the aim to improve the water wetness of biogenic chalk, was studied from a spontaneous imbibition point of view. To improve water wetness, SO 4 2− must act together with either Ca 2+ or Mg 2+. In both cases, the efficiency increased as the temperature increased. The water wetness of chalk can be improved if some of the carboxylic material adsorbed onto the chalk surface is displaced. A chemical mechanism discussing the mutual interaction between the potential determining ions and the chalk surface is proposed.
Petroleum Science
Most fractured carbonate oil reservoirs have oil-wet rocks. Therefore, the process of imbibing water from the fractures into the matrix is usually poor or basically does not exist due to negative capillary pressure. To achieve appropriate ultimate oil recovery in these reservoirs, a water-based enhanced oil recovery method must be capable of altering the wettability of matrix blocks. Previous studies showed that carbonated water can alter wettability of carbonate oil-wet rocks toward less oil-wet or neutral wettability conditions, but the degree of modification is not high enough to allow water to imbibe spontaneously into the matrix blocks at an effective rate. In this study, we manipulated carbonated brine chemistry to enhance its wettability alteration features and hence to improve water imbibition rate and ultimate oil recovery upon spontaneous imbibition in dolomite rocks. First, the contact angle and interfacial tension (IFT) of brine/crude oil systems were measured for several synthetic brine samples with different compositions. Thereafter, two solutions with a significant difference in WAI (wettability alteration index) but approximately equal brine/oil IFT were chosen for spontaneous imbibition experiments. In the next step, spontaneous imbibition experiments at ambient and high pressures were conducted to evaluate the ability of carbonated smart water in enhancing the spontaneous imbibition rate and ultimate oil recovery in dolomite rocks. Experimental results showed that an appropriate adjustment of the imbibition brine (i.e., carbonated smart water) chemistry improves imbibition rate of carbonated water in oil-wet dolomite rocks as well as the ultimate oil recovery.
SPE Improved Oil Recovery Conference, 2020
In our previous paper (SPE-190281-MS), we presented results from a suite of multiscale experiments to understand interactions occurring across crude oil/brine/carbonate rock interfaces with different brine compositions. A new atomic to molecular scale mechanism was proposed based on changes in adhesion energies at different length- and time-scales to explain SmartWater effects for improved oil recovery (IOR) in carbonates. It was also understood that SmartWater effect is due to three distinct but interrelated physico-chemical mechanisms, involving changes to the colloidal interaction forces, surface roughening due to dissolution and re-precipitation, and removal of pre-adsorbed organic-ionic ad-layers (termed ‘flakes’) from the rock surface.In the present study, we carried out surface forces apparatus (SFA) experiments to understand SmartWater IOR mechanisms at elevated temperatures and pressures (up to 150°C and 2,200 psi) representative of realistic reservoir conditions. The resul...