System and Method for De-Watering of Hydrocarbon Production Wells Using Electrolysis

This application claims benefit and priority to Canadian Application Number 3,240,941, filed on Jun. 7, 2024, the entirety of which is incorporated herein by reference.

The present invention relates to improvements in production of hydrocarbons from hydrocarbon-producing wells, and more particularly to a system and method for de-watering production wells using electrolysis which among other advantages reduces hydrostatic backpressure by such manner of de-watering and thereby improves performance of the well and avoids having to pump connate water which flows into the well, to surface.

During production of hydrocarbons from a wellbore situated within a hydrocarbon formation connate water in the form of “formation water” within the hydrocarbon formation will typically flow into the wellbore along with hydrocarbons via pathways in the hydrocarbon formation created after “fracking” of the formation.

Ingress of water into the wellbore of a producing well along with hydrocarbons is typically highly undesirable, and adds to the expense of producing hydrocarbons.

Specifically, ingress of water typically in liquid form (although substantially smaller amounts of water vapour may also flow) into the wellbore undesirably displaces hydrocarbons in the wellbore itself, as water is typically denser than oil, and further increases the hydrostatic pressure in the wellbore thereby reducing the ingress of hydrocarbons from the formation into the wellbore for production to surface.

In the energy field where hydrocarbons such as natural gas are produced from underground formations, water is frequently also produced along with the natural gas. Typically, as the formation fluid pressure decreases with age, a water column builds up in the wellbore as the gas is flowed to surface, until the hydrostatic pressure of the water column equals the reservoir pressure, and the well stops flowing gas. Only by removing the water column in the wellbore and preferably in the immediate region surrounding the wellbore will the gas begin to flow again.

Accordingly, in order to maintain a differential pressure gradient between the wellbore and the surrounding reservoir and thereby be able to preserve inflow of hydrocarbons into the wellbore and reduce the pressure in the wellbore to a pressure less than the pressure of fluids in the formation surrounding the well, formation water which flows into the wellbore is typically lifted to surface in either separate repeated de-watering intervals (when production of hydrocarbons from the wellbore is stopped) or alternatively (as is more typically the case) is continually pumped to surface along with the produced hydrocarbons in a water/hydrocarbon mixture or emulsion.

Problematically, therefore, increased energy need be expended in producing “wet” oil or formation water to surface, particularly where there is a high “water cut” in the produced fluids.

Further problematic is that the so-called “produced water” or “formation water” (ie. the “water cut” in the produced fluids) is typically brackish and frequently contains concentrated brines and other contaminates such as sulfides and often residual amounts of chemical fracking fluid and/or proppant. Its treatment and/or disposal, as more fully explained below, is problematic and costly, and where such produced water is produced with and co-mingled with produced hydrocarbons as typically occurs in the produced fluid, expensive equipment is required to further extract and separate hydrocarbons from the produced fluid/emulsion.

As of 2016, approximately 21 billion bbl (barrels; 1 bbl=42 U.S. gallons) of produced water were being generated annually in the United States from about 900,000 wells, with the states of Colorado, Montana, New Mexico, Utah and Wyoming alone producing approximately 430 million gallons of produced water per day.

Produced water is typically a complex mixture of dissolved and particulate organic and inorganic materials. The physical and chemical properties of formation water vary depending on the geologic age, depth, and geochemistry of the hydrocarbon-bearing formation, as well as the chemical composition of the oil and gas phases in the reservoir, and also may contain production chemicals such as residual fracking fluids and proppants to which the formation may have been exposed.

Produced water typically contains at least the same salts as seawater, with sodium and chloride the most abundant ions. The most abundant inorganic ions in high-salinity produced water are, in order of relative abundance, sodium, chloride calcium, magnesium, potassium, sulfate, bromide, bicarbonate, and iodide.

Produced water from sour oil/gas wells may contain also high concentrations of sulfide and elemental sulfur.

Table 1 below sets out typical concentrations (mg/kg or parts per million) of several elements and inorganic ions in produced waters of different geologic ages compared with average concentrations in 35% seawater:1. Produced Water, Overview of Composition, Fates, and Effects, July 2011

DOI:10.1007/978-1-4614-0046-2_1, In book: Produced Water (p. 4)

Treatment of produced water to remove residual contaminants, including organic and inorganic chemicals and elements such as metals, is very expensive, involving further expensive equipment to treat and store such water during the treatment process, or requires shipment of such treated water over large distances to offsite treatment facilities. Shipment of such produced water elsewhere for treatment via pipeline or truck is invariably prohibitively expensive. Moreover, in cold climates where temperatures frequently drop below 0° C., transportation offsite is simply not an option or would require mixing such produced water with costly antifreeze substances which may not be available at site, and which would require still-further treatment facilities at an opposite end of a pipeline to extract any such added antifreeze compounds from such produced water.

Accordingly, typically the only option to deal with produced water is to re-inject such produced water back into the hydrocarbon formation using pumps as a means of disposing of such produced water and at the same time as a method of maintaining pressure in the reservoir, or alternatively injecting such produced water in a wellbore in a different hydrocarbon formation (termed a disposal well), created specifically for sisposal applications.

Disadvantageously, however, additional pumping equipment and additional piping to strategically re-inject such produced water into the formation at various optimal locations therein, or into a disposal well, are required. Each alternative adds significantly to the cost of hydrocarbon production from a particular formation. Indeed, the amount of produced water from a particular hydrocarbon formation is often to such an extent and amount that the associated expense of dealing with the produced water makes hydrocarbon recovery from the formation prohibitively expensive, and thereby rendering hydrocarbon production from wellbore in such particular hydrocarbon formation economically unfeasible.

Accordingly, a serious need exists in the upstream hydrocarbon production industry for new, better, and economically viable methods for dealing with produced water and which ultimately reduce the operating costs of extracting hydrocarbons from underground formations.

In particular a serious need in the art exists for methods of de-watering wells which better enhance the recovery of hydrocarbons and overall profitability of hydrocarbon recovery from a wellbore, and which methods may further, due to ultimate reduced or eliminated costs in disposing or treating such water, increase profitability and ROI of a wellsite and render wells which would otherwise be non-profitable economically viable.

Electrolysis of water using a source of DC electricity applied respectively to each of a cathode and anode electrodes immersed in water which decompose water to produce hydrogen at the negative electrode (cathode) and oxygen at the positive electrode (anode) has been known since the 18century.

As regards the electrodes immersed in water, a reduction reaction occurs at the negatively charged cathode with electrons (e) from the cathode being provided at such location to proximate hydrogen cations to form hydrogen gas. At the positively charged anode, an oxidation reaction occurs with a reaction that produces oxygen gas and provides electrons to the anode to complete the electrical circuit.

Specifically, two half reactions occur at each of the anode and cathode in the electrolysis of water. The water, however, for the half reactions to occur typically needs to be acidic or basic (alkaline) or in an ionized solution.

In the presence of acid within the water, the equations are:

Alternatively, in the presence of base, such as in an alkaline water electrolysis process, the equations are:

Combining either half reaction pair and driving the reactions via an electrical potential and thus provision of electrical energy applied to the electrodes yields the same overall decomposition reaction of water into oxygen and hydrogen:

As may be seen from the above overall decomposition reaction (1) above the number of hydrogen molecules produced in the overall electrolysis process is twice the number of produced oxygen molecules arising from electrolysis.

Heterogeneous electro-catalysts, such as platinized electrodes, can also aid in the efficiency of the electrolysis reaction. Alternatively, nickel-metal/nickel-oxide plated electrodes may be used, which significantly lower the required voltage potential to drive the aforesaid electrolysis reaction.

U.S. Pat. No. 7,326,329 describes a method to produce hydrogen via electrolysis using a diaphragm-less electrolytic cell consisting of separate anode and cathode cells that is supplied by a DC power source.

U.S. Pat. No. 7,191,737 describes a method to produce hydrogen via electrolysis where the generated hydrogen is stored in a gas reservoir which is then directly provided to an internal combustion engine.

European Patent 1,716,602 describes a method to produce hydrogen via electrolysis using sunlight where a photovoltaic power cells is connected to the electrolyzer for generation of hydrogen.

U.S. Pat. No. 10,487,408 describes a method to produce hydrogen via electrolysis where the system consists of a first compartment with an electrode for reducing water to hydrogen and another separate second compartment with an electrode for generating oxygen with its electrode connected electrically to the electrode of the first compartment.

International Patent Application Publication No 2006/113463 describes an apparatus and method for production of hydrogen which uses a catalytic electrolysis cell.

U.S. Pat. No. 8,282,811 describes a multi-cell hydrogen production and compression device. The device is fed with water, and electrolysis is used to electrochemically split the water into oxygen gas and hydrogen protons. The hydrogen protons are attracted to the first anode to form hydrogen gas. Then, the moist hydrogen is fed to the anode of the second cell to which it is split again into protons. The protons are attracted to the cathode of the second cell. Due to the ability of differential pressure operation across the proton exchange membrane, this device claims to produce high pressure hydrogen at a higher efficiency than a single differential pressure cell or a single same pressure difference cell.

None of the aforementioned prior art publications teach or suggest producing hydrogen and oxygen under pressurization. Rather, each of such methods contemplate hydrogen and oxygen both being produced at atmospheric pressure, and that the hydrogen need subsequently be compressed if desired to be transported.

WO 2023/141725 entitled “Process to Produce Hydrogen and Oxygen from underground Systems” discloses carrying out electrolysis (ie the production of hydrogen and oxygen) under pressure, namely in a subterranean formation where water is supplied from ground surface to the subternation formation, suppling at least one electrolyzer within the subterranean formation, supplying the at least one electrolyzer in the subterranean formation with supply water via a supply tubing from surface, supplying electricity to the electrolyzer, and producing hydrogen gas at the electrolyzer and collecting and transporting the produced hydrogen gas to surface. The supply water may be introduced into the supply tubing and thus into the subterranean formation at elevated temperature and/or elevated pressure to assist the electrolysis and thus assist in the production of hydrogen and oxygen.

To like effect, U.S. Pat. No. 9,273,402 entitled “System and method for the manufacture, storage, and transportation of hydrogen and oxygen gas” teaches a deeply buried sealed production chamber capable of withstanding high pressures. Such production chamber is provided with water from surface, fed by gravity from a water source at surface to the deep sealed production chamber thereby producing water (16) in the bottom of the production chamber (10) under substantial pressure. Hydrogen and oxygen gas are produced in the water at the bottom of the production chamber (10) via electrolyis.

US 2016/0312646 entitled: “Electricity Generation and Water Desalination in Constructed Shafts Utilizing Geothermal Heat” teaches use of one or more subterranean shafts to convey seawater down to an operative depth of several miles, at which location electrical generators are driven via turbines to generate electricity, and such generated electricity conveyed to surface. Water which is conveyed downhole is flashed to steam and conveyed uphole to a condensation facility at surface which condences the desalinated steam back into pure water for distribution at surface.

CA 3,215,702 (AU2022/262094) entitled “Self-powered Downhole Electrolysis Tool” teaches a downhole a power generation system which uses inherent downhole energy (circulation of fluid or geothermal energy) to operate an electrolysis system that creates hydrogen and oxygen gas, which can be flowed to surface. Alternatively, the electrical power can be supplied downhole to the electrolysis system from for example a solar panel situated on surface.

None of the additional prior art publications of WO2023/141725, U.S. Pat. No. 9,273,402, US 2016/0312646 and/or CA 3,215,702 listed above teach or disclose a system of conducting electrolysis of formation water situated at a hydrocarbon production well, where the water is ambient formation water already existing downhole and within a wellbore.

Nor is there any teaching or suggestion in any of these subsequent prior art publications that reducing ambient fluid pressure in a production well or wellbore in comparison by dewatering using electrolyis so as improve or maintain a pressure gradient and thereby assist in hydrocarbon flow from the formation into the producing well.

Still further, nowhere is there any teaching or suggestion in any one of these subsequent prior art publications of producing a hydrocarbon to surface from an underground hydrocarbon formation combined with or separate from the produced hydrogen from the electrolysis process.

U.S. Pat. No. 11,371,329 entitled “Hydrogen Production by downhole electrolysis of Reservoir Brine for Enhanced Oil recovery” teaches use of an injection well in a hydrocarbon formation, which is used for electrolysis downhole of water so as to generate hydrogen, wherein the produced hydrogen improves flowability of oil in a formation. The method provides an electrochemical apparatus within an injection well situated in a reservoir, therein such that injection water of the injection wellbore is introduced into the interior of the electrochemical apparatus (col. 2, lines 2-4), and hydrogen produced. Alternatively, the injection wellbore is located in a water bearing formation, where a fluid within the water bearing formation includes injection water (col. 2, lines 28, 29). Electrical power is introduced into the electrochemical apparatus such that a portion of the injection water is converted into a product gas which includes hydrogen gas and oxygen gas. The product gas bubbles travel into the formation, where they react with a reservoir hydrocarbon of the formation to form a production fluid that is produced through a separate production wellbore spaced apart and closer to the earth's surface (col.2, lines 35-46). The wetability of the formation is altered with the product gas bubbles, reducing the viscosity of the oil and allowing it to flow easier in the formation The electrical power can be provided from surface via a solar photovoltaic panel.

Although U.S. Pat. No. 11,371,329 does incidentally disclose, as part of the concept of generating hydrogen gas bubbles in a formation to increase flowability of hydrocarbons in the formation, that “the use of water (from the formation) to form the product gas (ie hydrogen and oxygen) also reduces the adverse effect of water encroachment into oil and gas producing wells” (ref. col. 1, lines 55-58), such disclosed method teaches use of a separate injection well, spaced apart from the production well (preferably below it), which due to such remoteness from the location of the production well thereby fails to most efficiently prevent ingress of formation water in the region of the production wellbore. Again, therefore, this further reference fails to teach conducting electrolysis of formation water at and within a hydrocarbon production well.

The present invention has, as one of its objects as regards certain of its embodiments, providing a system and method for de-watering hydrocarbon production wells without having to produce (ie. pump) connate water which flows into the well to surface along with produced hydrocarbons.

The present invention has as another of its objects, as regards certain of its embodiments, providing a system and method of purifying contaminated water downhole, which would otherwise have had to be produced to surface in contaminated form along with produced hydrocarbons.