Field of the Invention

The present invention relates to the field of enhanced oil recovery (abbreviated EOR).

Background of the Invention

Enhanced oil recovery (abbreviated EOR), also called tertiary recovery, is the extraction of crude oil from an oil field that cannot be extracted otherwise. EOR can extract 30% to 60% or more of a reservoir's oil, compared to 20% to 40% using primary and secondary recovery. According to the US Department of Energy, carbon dioxide and water are injected along with one of three EOR techniques: thermal injection, gas injection, and chemical injection.

Crude oil production from reservoirs can include up to three distinct phases: Primary, Secondary, Tertiary (EOR). The tertiary stage can be extraction of crude oil by using chemicals in the injection brine to the oil reservoir.

Carbonate reservoirs are characterized as a neutral to oil wet system. It is important to modify the carbonate reservoir surface to water wet in order to increase oil recovery.

Enhancing oil recovery system include: oil-water -solid. The composition of the injection brine is crucial for efficiency of the wettability of the carbonate surface. Summary of the Invention

According to some demonstrative embodiments there is provided herein a solution for the recovery of oil from carbonate reservoirs comprising Polyhalite and injected water selected from the group including sea water, diluted sea water, desalinated seawater, produced water, Aquifer water, river water or a combination of thereof

According to some demonstrative embodiments the injected water may include sea water enriched with bivalent salt adding surface materials.

According to some demonstrative embodiments the solution may further comprise bivalent salts of magnesium sulphate and/or calcium sulphate.

According to some demonstrative embodiments, there is provided herein a method for recovering oil from carbonate reservoirs comprising adding Polyhalite to injected water; injecting the injected water to facilitate oil recovery; and wherein said injected water selected from the group including sea water, diluted sea water, desalinated seawater, produced water, Aquifer water, river water or a combination of thereof

According to some embodiments, the solution of the present invention comprises bivalent ions such as Sulphate, Magnesium, Calcium in various concentrations to increase oil recovery, e.g., wherein the source of the bivalent ions may be Polyhalite.

Polyhalite is an evaporite mineral, a hydrated sulfate of potassium, calcium and magnesium with formula: K2Ca2Mg(SO4)4 2H2O. Polyhalite is often used as a fertilizer since it contains four important nutrients and is low in chloride:

48% SO3 as sulfate

14% K ₂ O

6% MgO

17% CaO

According to some demonstrative embodiments, using Polyhalite in injected water may enhance the recovery of oil from reservoirs.

According to some embodiments, the injected water may preferably be sea water.

According to some embodiments, other sulphate minerals may be added to the injected water, whether instead of Polyhalite or in addition to Polyhalite. According to some embodiments, the sulphate minerals may be selected from the group including Anhydrite, Gypsum, Kieserite, Epsomite. Glauberite, Blodite, Langbeinite, Kainite, Schonite,

According to some embodiments, the use of Polyhalite in the injected water allows for the release of bivalent ions which contribute to the wettability of carbonate reservoir.

According to some embodiments, the carbonate surface has a positive charge and chloride anions attached to the surface. Decreasing sodium chloride concentration or increasing subplate ions may have an impact on oil recovery.

According to some embodiments, Sulphate anions may neutralize the positive charge on the carbonate surface, and allow calcium cations to detach the crude oil from the pores of the oil well walls. According to some embodiments, Magnesium ions may also contribute to oil recovery by increasing the wettability properties of oil- carbonate surfaces.

While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.

It will be appreciated that various features of the invention which are, for clarity, described in the contexts of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable subcombination. It will also be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove.