Enhanced oil recovery process to inject low salinity water and gas in carbonate reservoirs

a technology of carbonate reservoir and oil recovery process, which is applied in the direction of fluid removal, chemistry apparatus and processes, borehole/well accessories, etc., can solve the problems of reducing time, low efficiency, and high cost of full-field low salinity water injection, and achieves enhanced oil recovery process, high carbon dioxide solubility, and improved efficiency

Inactive Publication Date: 2015-08-20
COLORADO SCHOOL OF MINES
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  • Abstract
  • Description
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Benefits of technology

[0010]By applying low salinity water-alternating-gas (LS-WAG) approach the enhanced oil recovery process is effective in mobilizing residual oil from oil-wet carbonate reservoirs. This EOR process, for example, can be applied to one of the largest carbonate reservoirs, Upper Zakkum, located offshore Abu Dhabi. This Upper Zakkum reservoir is currently undergoing conventional seawater flooding at injection rate of 800 MBW / day. The average daily oil production is 560 MSTB. This LS-WAG EOR process can be beneficial to this field to produce significant amount of additional oil.
[0011]The present invention takes advantage of the synergistic effect of mobilizing residual oil due to both low salinity water and gas solvents (CO2, NGL, LPG, nitrogen gas, CO2+NGL mixture, CO2+N2+NGL mixture, N2+NGL mixture and mixtures thereof). Though not wanting to be bound by theory, the low salinity water is believed to alter the wettability state of the reservoir towards water-wet and lower interfacial tension (IFT) between brine and oil. The solubility of carbon dioxide is higher in low salinity water as compared to the solubility of carbon dioxide in higher salinity water, which means higher carbonic acid concentration when applied with low salinity water, and this leads to improved wettability alteration towards water-wet state and further reduction in IFT. In addition, there is a decrease in oil viscosity and further increase in oil swelling can be achieved compared to a conventional WAG process, resulting in improved oil mobility. Thus, the method results in enhanced oil recovery from the reservoir.
[0012]An aspect of the invention is a method to enhance recovery of oil in a hydrocarbon reservoir. The method includes injecting low salinity water into the reservoir, then injecting a gas into the reservoir after the injection of the low salinity water into the reservoir.

Problems solved by technology

Reduces time—Full field low salinity water injection is expensive because it has to displace the already injected high salinity water to be beneficial.
Miscibility achieved—If N2 is used as injection gas, the minimum miscibility pressure (MMP) is usually high in most reservoirs, and miscibility may not be achieved.

Method used

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  • Enhanced oil recovery process to inject low salinity water and gas in carbonate reservoirs
  • Enhanced oil recovery process to inject low salinity water and gas in carbonate reservoirs
  • Enhanced oil recovery process to inject low salinity water and gas in carbonate reservoirs

Examples

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example

Example 1

[0054]Two core-flood experiment of seawater flood, followed by three sets of low salinity-water flood, flowed by CO2 flood is performed on Facies 5 (F5) of Reservoir I core samples from a giant carbonate oil field in the Middle East. Facies description and geologic study of the reservoir can be found in Jobe (2013). Cores were prepared, cleaned using toluene and methanol. The petrophysical properties such as permeability and porosity are measured using Core Measurement System (CMS-300). Table 1 lists rock properties of samples used in the two core-flood experiments. The core type for all samples was F5 carbonate core (composite core). The diameter of the samples was about 1.5 inches and the PV was about 29.98 cc for Example 1 and 34.864 cc for Example 2. The miscible CO2 flooding following seawater and low salinity waterflooding (e.g. LS2, LS4, LSx) on composite carbonate cores. Eight weeks of aging applied. The miscible CO2 flooding following seawater and low salinity wate...

example 2

[0063]The core-flood protocol applied to the second core-flood on a second F5 sample from Reservoir I was similar to the first core-flood protocol. About 52.8% oil was recovered during waterflooding, about 5.2% additional oil was recovered during LS2 flooding, and about 0.4% and no additional oil was recovered during LS4 and LS50 flooding cycles, respectively. Finally, about 25% additional oil was recovery during about 10 PV continuous miscible CO2 flooding. FIG. 5 illustrates the oil recovery factor and pressure drop as a function pore volume injected.

example 3

[0064]The interfacial tension (IFT) between brine and oil as well as wettability of core discs with oil was measured at ambient conditions. Drop Shape Analyzer, DSA 100, was used to measure contact angles between solids and fluids and IFT between different fluids. For both IFT and wettability measurements, the effect of salinity of brine was investigated. About 32° API gravity crude oil from Reservoir I was used in both IFT and wettability measurement. Also the Reservoir I formation brine (FB) was used in the IFT and wettability measurements. Pendant drop method was used to determine the IFT, whereas, captive oil droplet contact angle measurement method was applied during the contact angle measurements. Detailed discussion on the IFT and contact angle measurement and additional results can be found in Teklu et al. (2014), Teklu et al., (2015), and Alameri et al. (2014).

[0065]Wettability measurements were performed on crude-aged F5 carbonate, Berea sandstone, and Three Forks core dis...

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Abstract

The present invention relates to a method to enhance oil recovery from a hydrocarbon reservoir. One aspect of the invention includes injecting high salinity water into the reservoir followed by alternating the injection of low salinity water and gas.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61 / 941,869 filed Feb. 19, 2014, which is incorporated herein in its entirety by reference.FIELD OF THE INVENTION[0002]The invention relates to a method to enhance the recovery of oil in a hydrocarbon reservoir with the injection of low salinity water and gas, such as carbon dioxide, natural gas liquids, liquefied petroleum gas or a gas mixture.BACKGROUND OF INVENTION[0003]Conventional waterflooding is widely used globally in carbonate oil reservoirs. The ultimate oil recovery from primary production and waterflooding is significantly less than 50%. To recover additional residual oil after waterflooding, gas flooding (such as CO2), low salinity waterflooding, or other enhanced oil recovery (EOR) methods can be implemented. However, low salinity waterflooding is not economical because it has to displace previously injected higher salinit...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): E21B43/16
CPCC09K8/594E21B43/164E21B43/166
Inventor TEKLU, TADESSE WELDUALAMERI, WALEED SALEMGRAVES, RAMONA M.KAZEMI, HOSSEINALSUMAITI, ALI M.
Owner COLORADO SCHOOL OF MINES
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