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_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 209418, “Surfactant Enhanced Oil Recovery From Tight Carbonates: Core-Scale Experiments to Reservoir-Scale Modeling,” by Yue Shi, SPE, and Kishore Mohanty, SPE, The University of Texas at Austin. The paper has not been peer reviewed. _ Most carbonate reservoirs are oil-wet/mixed-wet and heterogeneous at multiple scales. The majority of the injected water flows through the high-permeability regions and fractures and bypasses the oil in the matrix because of high negative capillary pressure (Pc). To enhance oil recovery from such reservoirs, the sign of the Pc should be changed by wettability alteration (WA) or the Pc should be reduced by lowering interfacial tension (IFT). In the complete paper, surfactants that can either alter wettability or develop ultralow IFT were identified through laboratory measurements for the target carbonate reservoir. Introduction Contact-angle, IFT, phase-behavior, and imbibition tests were first performed, and surfactants that can either alter wettability or develop ultralow IFT were identified. Then, a laboratory-scale imbibition model was built with commercial reservoir simulation software. A sensitivity study was performed to evaluate the effects of residual oil saturation (Sor), alteration of Pc and relative permeability (Kr), IFT, and matrix scale on oil recovery by surfactant. Next, the laboratory-scale imbibition model was used to history match the experimental data and parameters were tuned for reservoir-scale simulation. Finally, a 3D layered field-scale model was developed to study the performance of the selected surfactants in injection/soak/production (ISP) tests. Materials Eight anionic surfactants (An 1 through An 8) and two quaternary ammonium cationic surfactants (Cat 1 and 2) were used. Silurian dolomite (SD) outcrop cores were used in this study. Fluid samples were obtained from a West Texas dolomite-rich reservoir. The oil has a density of 0.84 g/mL at 25°C and a viscosity of 7.46 cp at reservoir temperature (35°C). It has an acid number of 0.25 mg KOH/g and a base number of 1.0 mg KOH/g. The reservoir has been waterflooded for years, and total dissolved solids of brine has decreased from 112,668 to 40,393 ppm for recent produced water (PW). The authors detail the methodology for aqueous-stability, contact-angle-measurement, IFT-measurement, phase-behavior, and spontaneous-imbibition tests in the complete paper.
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Waterflooding (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Chemical flooding methods (0.72)
- Reservoir Description and Dynamics > Reservoir Simulation > History matching (0.68)
Abstract Most carbonate reservoirs are oil-wet/mixed-wet and heterogenous at multiple scales. Majority of the injected water flows through the high permeability regions/fractures and bypass the oil in the matrix due the high negative capillary pressure (Pc). To enhance oil recovery from such reservoirs, the sign of the Pc should be changed by wettability alteration (WA) or the Pc should be reduced by lowering interfacial tension (IFT). In this study, surfactants which can either alter wettability or develop ultra-low IFT were identified through laboratory measurements for the target carbonate reservoir. The performance of these two types of surfactants was systematically evaluated at the core scale and scaled-up to the reservoir scale. A reservoir-scale model was developed to simulate injection-soak-production (ISP) tests and evaluate performance of the selected surfactants at the field scale. Experiments showed that quaternary ammonium cationic surfactants have excellent WA ability, while a series of propoxy sulfate anionic surfactants showed intermediate WA and ultra-low IFT. Spontaneous imbibition tests showed that WA surfactants have fast initial oil production, while ultra-low IFT surfactants has low initial oil rate but higher final oil recovery, which was validated by mechanistic simulation. Low IFT results in low Pc and slow imbibition, but also triggers gravity-driven drainage. For ultra-low IFT system, gravity drainage is more dominant than WA, and Pc-alteration is less important than relative permeability (Kr) alteration. As reservoir thickness increases, Kr-alteration is more important than Pc-alteration. Gravity drainage is expected to be scaled up by length of matrix (L), while Pc-driven imbibition is scaled by L. Field-scale simulation showed that low-IFT surfactant has better injectivity than WA surfactant during injection phase. In soaking phase, spontaneous imbibition by WA surfactant is much more significant than that by low-IFT surfactant. In production phase, post-waterflood achieved higher oil recovery from low-IFT surfactant treated matrix due to its low residual oil saturation and high oil relative permeability.
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.46)
- North America > United States > Wyoming > Bighorn Basin > Phosphoria Formation (0.99)
- North America > United States > Texas > Permian Basin > Delaware Basin > Yates Field > Whitehorse Group > Word Group > San Andreas Formation (0.99)
- North America > United States > Texas > Permian Basin > Delaware Basin > Yates Field > Whitehorse Group > Grayburg Formation > San Andreas Formation (0.99)
- (3 more...)
- Reservoir Description and Dynamics > Reservoir Simulation > Scaling methods (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Waterflooding (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Chemical flooding methods (1.00)
Lab Study and Field Application of Surfactant Induced Imbibition for Low Permeability Reservoirs
Zhang, Fan (State Key Laboratory of Enhanced Oil Recovery, PetroChina Research Institute of Petroleum Exploration & Development) | Zhu, Youyi (State Key Laboratory of Enhanced Oil Recovery, PetroChina Research Institute of Petroleum Exploration & Development) | Luo, Wenli (State Key Laboratory of Enhanced Oil Recovery, PetroChina Research Institute of Petroleum Exploration & Development) | Cai, Hongyan (State Key Laboratory of Enhanced Oil Recovery, PetroChina Research Institute of Petroleum Exploration & Development) | Song, Wenfeng (State Key Laboratory of Enhanced Oil Recovery, PetroChina Research Institute of Petroleum Exploration & Development) | Zhang, Qun (State Key Laboratory of Enhanced Oil Recovery, PetroChina Research Institute of Petroleum Exploration & Development) | Zhou, Zhaohui (State Key Laboratory of Enhanced Oil Recovery, PetroChina Research Institute of Petroleum Exploration & Development)
Abstract Low permeability reservoirs are widely distributed in various countries, which contribute an important percentage of oil output in the world. At present the main exploitation mode is water flooding, but the oil recovery is very low. So it is very necessary to develop effective development technology. Chemical flooding technique is one of effective ways to enhanced oil recovery (EOR). However, low permeability may cause injection difficulty of conventional chemical agents (polymers and formulations of chemical combination flooding). Moreover, high temperature or high salinity condition may cause decomposition of the surfactant and polymer with poor long-term stability. For these harsh condition reservoirs, surfactant induced imbibition is an important and promising technology to enhance oil recovery. The key technology is to develop high efficiency surfactant with low cost. In this paper, the novel anionic surfactant has been developed with good capabilities, including good wettability alteration performance, low adsorptions, wide adaptability, good heat resistant and salt tolerant abilities, and high oil displacement efficiencies. Above all, the field test results are good in China. The anionic surfactant could alter wettability from oil-wet to water-wet effectively and had good stripping film capacity. Contact angles were changed remarkably from more than 130° to less than 50°, and oil film could be peeled off in 180 seconds rapidly. The surfactant had good anti-adsorption ability, and it could maintain ultra-low interfacial tension for 5 times adsorption with the natural sand. The dynamic adsorptions of the anionic surfactant on the rock were less than 1.0 mg/g rock, which will meet the requirement of field applications. The anionic surfactant has wide adaptability and good heat resistant and salt tolerant capabilities. The maximum temperature was 160°C, and the maximum salinity was 220,000 mg/L. Core flooding tests demonstrated an average incremental recovery of 12.5% was achieved utilizing imbibition technology. For Qinghai oilfield (low permeability 26×10µm, high temperature 126°C, high salinity 200,000 mg/L) in China, field pilot test of imbibition oil recovery technology was successful. 18 tons of imbibition agents were injected and increased oil production of 3660 tons. Excellent properties of the anionic surfactant indicate that it is a promising surfactant, which can be applied in low permeability reservoirs, especially for high temperature and high salinity reservoirs.
- Asia > China > Qinghai Province (0.26)
- North America > United States > Louisiana (0.25)
- Europe > United Kingdom > North Sea > Central North Sea (0.25)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (27 more...)
Abstract Surfactant injection can be used as an EOR technique by either altering the wettability of reservoir and/or reducing IFT of water and oil. How to balance the functionality of wettability alteration and IFT reduction of a surfactant flooding process for oil wet carbonate reservoirs is still paradox for surfactant technology selection. In this study, the effects of IFT reduction and wettability alteration by surfactant on EOR for a carbonate reservoir were studied by using two kind surfactant systems individually. For IFT reduction surfactant, the surfactants which can reach IFT at different level and ultralow IFT were synthesized based on molecular design method by only changing the structure of surfactant and without any formulation process. Moreover, these surfactants are also has a little effect on wettability alteration proven by contact angle test. The surfactants for wettability alteration study are selected based on contact angle method and also on the principle of "less effect on IFT property". The static and dynamic imbibition tests are carried out to understand the contribution of wettability alteration and IFT reduction mechanism individually to enhance oil recovery, hence, the surfactant flooding technique for an oil wet carbonate reservoir could be optimized.
Abstract The goal of this work is to pursue strategies to improve oil recovery in highly fractured carbonate reservoirs by altering the wettability from oil-wet to preferentially water-wet at high temperature (100°C or above), high salinity, and especially high hardness environments. Cationic surfactants and anionic surfactants were investigated for their compatibility with hard brine and thermal/hydrolytic stability. Sequestration agents were added to improve aqueous solubility. The performance of surfactant formulations was evaluated by measuring contact angles on calcite plates and spontaneous imbibition in originally oil-wet dolomite cores. Cationic surfactants altered the wettability of oil-aged calcite plates towards a more water-wet state in the presence of hard brines; oil recovery by spontaneous imbibition from dolomite cores was 50–65% OOIP. Anionic surfactant formulations changed the carbonate wettability to strongly water-wet only when the brine salinity and divalent ion concentration were reduced. The wettability could be altered in hard brines if a sequestration agent (e.g. EDTA) is added to anionic surfactant formulations; up to 45% OOIP was recovered by spontaneous imbibitions. EDTA provides alkalinity, saponification, chelation of divalent ions, and dissolution of dolomite; these mechanisms are responsible for the increase in imbibition rate and ultimate oil recovery in fractured carbonates.
- Geology > Mineral (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Dolomite (0.99)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.94)
- North America > United States > Texas > Permian Basin > Delaware Basin > Yates Field > Whitehorse Group > Word Group > San Andreas Formation (0.99)
- North America > United States > Texas > Permian Basin > Delaware Basin > Yates Field > Whitehorse Group > Grayburg Formation > San Andreas Formation (0.99)
- Europe > Norway > North Sea > Central North Sea > Central Graben > Block 2/8 > Valhall Field > Tor Formation (0.99)
- (3 more...)