FIELD OF THE INVENTION

The present disclosure generally provides systems and methods for producing steam for use in various applications, including enhanced oil recovery processes. In particular, the present disclosure provides systems and methods that comprise an electrode boiler and one or more heat exchangers and use of such boiler and heat exchangers for steam production.

BACKGROUND

Steam is useful in many applications, particularly in thermal enhanced oil recovery (EOR) technique. Thermal EOR generally involves injecting steam into an oil-bearing formation to free up and reduce the viscosity of the oil. Representative steam injection techniques include cyclic, steamflood, steam-assisted gravity drainage (SAGD), and other strategies using vertical and/or horizontal injection wells, or a combination of such wells, along with continuous, variable-rate, and/or intermittent steam injection in each well.

Thermal EOR operations often require steam production over a period ranging from many days to many years. During recovery of hydrocarbons from wells, water containing some residual hydrocarbons is also produced from the wells (“produced water”). The produced water may have high levels of calcium and magnesium, a high salt concentration, high organic content in the form of dissolved oil, and may be more acidic than other boiler feedwater that has a pH closer to neutral pH. Typically, this produced water can be provided to gas-fired boilers, after minimal or no treatment, as Boiler Feedwater (BFW) to generate the steam.

A representative gas-fired steam production system is a Once Through Steam Generator (OTSG), such as illustrated in, for example, US20110017449. An OTSG produces steam by contacting water in a single pass heat exchanger with the heat from a combustion process. Yet another steam generating system includes heat recovery steam generators (HRSG) contacting the combustion gas from a gas turbine in a single pass heat exchanger with the water, operating in a continuous mode. However, both rely on fossil fuel firing and hence emit C02, which contributes significantly to the carbon intensity of the crude oil produced.

Concentrated solar power has been employed to generate steam through directing sunlight onto a pipe containing either the produced water to directly generate steam (such as US2020185586 or US20140318792), or a heat transfer fluid which is sent to a heat exchanger to generate steam from the produced water (such as US4513733). However, the cost of concentrated solar technology can be relatively higher than other renewable resources.

Another representative steam production system involves electric-powered boilers, such as disclosed by US6205289. However, the produced water from EOR is typically not suitable for use as BFW for the electrode boilers referenced in this application. While the produced water can be treated to remove hardness, hydrocarbons, salts and other impurities, such treatment would usually be cost prohibitive for thermal EOR applications that often need large quantities of produced water to be converted to steam. While other electric boilers could be used, like resistive heaters, these have similar challenges as those of electrode boilers in that extensive water clean up could be required, while they are also significantly less costs effective than electrode boilers.

As such, there is still a need for steam producing systems and methods that address these challenges.

SUMMARY

Accordingly, the present disclosure provides a method for generating steam comprising providing feedwater having an electrical conductivity of less than 200 pS/cm to an electrode boiler, wherein the electrode boiler has a capacity of at least 5 megawatts (MW); converting the feedwater to saturated steam by the electrode boiler, wherein the saturated steam has a pressure in a range from at least 3.5 MPa and up to 14 MPa and a temperature in a range from 240 degrees C and up to 340 degrees C; providing the saturated steam as a first fluid to a heat exchange component; providing water having an electrical conductivity of more than 200 pS/cm as a second fluid to the heat exchanger; heating the second fluid in the heat exchange component through indirect thermal transfer with the saturated steam to generate wet steam having a temperature lower than the temperature of the saturated steam by a range from 2 degrees C and up to 30 degrees C and a pressure in a range from at least 0.5 MPa and up to 13 MPa; at least partially condensing the saturated steam in the heat exchange component through indirect thermal transfer with the second fluid to produce a condensed fluid; and providing at least a portion of the condensed fluid to the electrode boiler for use as part of the low-conductivity water to generate said saturated steam.

The present disclosure also provides for a system for generating steam comprising an electrode boiler configured to convert feedwater having an electrical conductivity of less than 200 pS/cm to saturated steam having a pressure in a range from 3.5 MPa and up to 14 MPa and a temperature in a range from 240 degrees C and up to 340 degrees, wherein the electrode boiler has a capacity of at least 5 megawatts (MW); a heat exchange component in fluid communication with the electrode boiler to receive the saturated steam, where said heat exchanger is configured to receive water having an electrical conductivity of more than 200 pS/cm as a second fluid to the heat exchanger and allow indirect thermal transfer between the saturated steam and the second fluid to convert (i) the second fluid into wet steam having a temperature lower than the temperature of the saturated steam by a range from 2 degrees C and up to 30 degrees C and a pressure in a range from at least 0.5 MPa and up to 13 MPa and (ii) the saturated steam into a condensed fluid. The system further comprises a recycle line between an outlet of the heat exchanger and an inlet of the electrode boiler to provide at least a portion of the condensed fluid to the electrode boiler for use as the feedwater generate the saturated steam.

At least a portion of the wet steam may be employed for injection into a subsurface hydrocarbon formation for hydrocarbon recovery. The system is particularly suitable to supply wet steam to equipment for steam injection in thermal EOR.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of the present disclosure and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to one having ordinary skill in the art and the benefit of this disclosure.

FIG. 1 is a schematic illustration of a system that includes an electrode boiler and a heat exchanger configured in accordance with an embodiment of the presently disclosed technology.

FIG. 2 is a schematic illustration of a system that includes an electrode boiler and two heat exchangers configured in accordance with another embodiment of the presently disclosed technology.

FIG. 3 is a schematic illustration of a system that includes an electrode boiler and two heat exchangers configured in accordance with yet another embodiment of the presently disclosed technology.

DETAIFED DESCRIPTION

The present disclosure generally provides systems and methods for producing steam for use in enhanced oil recovery processes, including systems and methods comprising an electrode boiler and one or more heat exchangers for steam production. Specific details of various embodiments of the disclosed steam production systems and methods are described below in detail as illustrated in the accompanying drawings. References to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, as an option but every embodiment may not necessarily but can include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. In some instances, well known process steps and/or structures may have not been described in detail in order to not unnecessarily obscure the present invention. The depiction of some of such features in the figures does not indicate that all of them are depicted. In addition, when like elements are used in one or more figures, identical reference characters will be used in each figure, and a detailed description of the element will be provided only at its first occurrence.

Pressure values are specified in units of gauge pressure.

A method is proposed for generating steam comprising providing feedwater having an electrical conductivity of less than 200 pS/cni to an electrode boiler. The feedwater is converted to saturated steam by the electrode boiler. The saturated steam is provided as a first fluid to a heat exchange component. A second fluid, consisting of water having an electrical conductivity of more than 200 pS/cni is also proficed to the heat exchange component. In the heat exchange component, the second fluid is heated through indirect thermal transfer with the saturated steam, to generate wet steam having a temperature lower than the temperature of the saturated steam and a pressure in a range from at least 0.5 MPa and up to 13 MPa. The saturated steam is thereby at least partially condensed in the heat exchange component through said indirect thermal transfer with the second fluid, to produce a condensed fluid. At least a portion of the condensed fluid is provided to the electrode boiler for use as part of the low-conductivity water to generate said saturated steam.

The electrode boiler may have a capacity of at least 5 megawatts (MW).

The saturated steam preferably has a pressure in a range from at least 3.5 MPa and up to 14 MPa, and a temperature in a range from 240 degrees C and up to 340 degrees C. The wet steam discharged from the heat exchange component may have a temperature lower than the saturation steam by a range from 2 degrees C and up to 30 degrees C.

Optionally, at least 50%, preferably at least 75%, or more preferably at least 99% of the condensed fluid is provided to the electrode boiler for use to generate said saturated steam. Optionally, the step of heating the second fluid in the heat exchange component to generate wet steam comprises providing a first portion of the saturated steam to a first heat exchanger of the heat exchange component; providing the second fluid to the first heat exchanger; heating the second fluid in the first heat exchanger through indirect thermal transfer with the first portion of the saturated steam to generate a pre-heated second fluid; providing the pre-heated second fluid to a second heat exchanger of the heat exchange component; providing a second portion of the saturated steam to the second heat exchanger; and heating the pre-heated second fluid in the second heat exchanger through indirect thermal transfer with the second portion of the saturated steam to generate the wet steam.

The first heat exchanger may provide from 30% and up to 45% of the total thermal energy needed to convert the second fluid to wet steam. Preferably, the pre-heated second fluid is in liquid phase. In this context, a small amount of vapor, for example up to 0.1 % in mass may be acceptable.

Optionally, the step of heating the second fluid in the heat exchange component to generate wet steam comprises providing the second fluid to a first heat exchanger of the heat exchange component; heating the second fluid in the first heat exchanger through indirect thermal transfer with a condensed fluid from a second heat exchanger of the heat exchanger component to generate a pre heated second fluid; providing the pre-heated second fluid to the second heat exchanger; providing the saturated steam to the second heat exchanger; heating the pre-heated second fluid in the second heat exchanger through indirect thermal transfer with the saturated steam to generate the wet steam; and at least partially condensing the saturated steam in the second heat exchanger through indirect thermal transfer with the pre-heated second fluid to produce the condensed fluid.

The first heat exchanger may provide from 30% and up to 45% of the total thermal energy needed to convert the second fluid to the wet steam. Preferably, the pre-heated second fluid is in liquid phase. In this context, a small amount of vapor, for example up to 0.1% in mass may be acceptable.

An advantage of pre-heating the second fluid to a temperature whereby the second fluid is still substantially in full liquid phase, is that the control and operation of the second heat exchanger is decoupled from any temperature variations in the initial feed of the second fluid. This improves the steam quality control.

Optionally, the method further comprises providing at least a portion of the wet steam for injection into a subsurface hydrocarbon formation for hydrocarbon recovery. Optionally, the electricity powering the operation of the electrode boiler comprises green energy, optionally selected from a group consisting of solar photovoltaic panels, wind turbines, hydropower, a battery charged with any one or more of the foregoing, and any combination thereof. Optionally, at least a portion of the electricity is generated by one or more solar photovoltaic panels. Optionally, the electrode boiler is powered completely by green energy produced by a power source that is not connected to a public electric grid. The power source and the electrode boiler may be connected to one another with an islanded power grid. Optionally, the power source comprises an islanded solar PV microgrid.

Optionally, the method further comprises providing at least a portion of the green energy for use by the hydrocarbon recovery site.

A system for generating steam is proposed, which comprises an electrode boiler configured to convert feedwater having an electrical conductivity of less than 200 pS/cm to saturated steam, a heat exchange component in fluid communication with the electrode boiler to receive the saturated steam, where said heat exchanger is configured to receive water having an electrical conductivity of more than 200 pS/cni as a second fluid to the heat exchanger and allow indirect thermal transfer between the saturated steam and the second fluid to convert (i) the second fluid into wet steam having a temperature lower than the temperature of the saturated steam and (ii) the saturated steam into a condensed fluid. The system further comprises a recycle line between an outlet of the heat exchanger and an inlet of the electrode boiler to provide at least a portion of the condensed fluid to the electrode boiler for use as the feedwater generate the saturated steam.

The system is particularly suitable to supply wet steam to equipment for steam injection in thermal EOR. The heat exchange component may be fluidly connected to a wet steam conduit to receive the wet steam from the heat exchange component and route the wet steam to equipment for steam injection in thermal EOR. The wet steam conduit may suitably be connected to equipment for steam injection in thermal EOR

Optionally, the heat exchange component further comprises a first heat exchanger in fluid communication with the electrode boiler to receive a first portion of the saturated steam, wherein the first heat exchanger is configured to receive the second fluid and allow indirect thermal transfer between the first portion of the saturated steam and the second fluid to generate a pre-heated second fluid; and a second heat exchanger in fluid communication with the first heat exchanger to receive the pre-heated second fluid, wherein the second heat exchanger is configured to receive a second portion of the saturated steam and allow indirect thermal transfer between the second portion of the saturated steam and the pre-heated second fluid to generate the wet steam; where the first heat exchanger has a heat transfer surface area less than a heat transfer surface area of the second heat exchanger.

Optionally, the heat exchange component further comprises: a first heat exchanger in fluid communication with a second heat exchanger to receive a condensed fluid, wherein the first heat exchanger is configured to receive the second fluid and allow indirect thermal transfer between the condensed fluid and the second fluid to generate a pre-heated second fluid. The second heat exchanger is in fluid communication with the first heat exchanger to receive the pre-heated second fluid, wherein the second heat exchanger is configured to receive the saturated steam and allow indirect thermal transfer between the saturated steam and the pre-heated second fluid to generate the wet steam; where the first heat exchanger has a heat transfer surface surface less than a heat transfer surface area of the second heat exchanger.

Optionally, the heat transfer surface area of the first heat exchanger is less than 50% the heat transfer surface area of the second heat exchanger. Optionally, the electricity powering the operation of the electrode boiler comprises green energy, optionally selected from a group consisting of solar photovoltaic panels, wind turbines, hydropower, a battery charged with any one or more of the foregoing, and any combination thereof. Optionally, the electrode boiler is powered completely by green energy produced by a power source that is not connected to a public electric grid. The power source and the electrode boiler may be connected to one another with an islanded power grid. Optionally, the power source comprises an islanded solar PV microgrid.

FIG. 1 is a partially schematic illustration of an overall system 100 used to generate steam. System 100 comprises at least one electrode boiler 102 (may also be referred to as an electrode boiler) in fluid communication with heat exchange component 104. It is understood by one of ordinary skill that the at least one electrode boiler can include a plurality (i.e., two or more) of electrode boilers connected in parallel. Electrode boiler 102 receives feedwater, such as via line 124 and/or line 116 as further discussed below, having an electrical conductivity of less than 200 micro Siemens per cm (pS/cm), preferably less than 10 pS/cm, and most preferably less than 5 pS/cm, and produces saturated steam with a pressure in a range from 3.5 MPa and up to 14 MPa, including from 3.5 MPa and up to 14 MPa, preferably from 6.5 MPa and up to 14 MPa, and more preferably from and up to 8.5 MPaal4 MPa. The saturated steam has a corresponding saturated steam temperature in a range from 240 and up to 340 degrees C. At least a portion of the saturated steam is provided to first inlet 106 of heat exchange component 104 via a suitable means, such as line 108, which saturated steam can be used to heat up a second fluid in heat exchange component 104 to convert the second fluid to wet steam. One of ordinary skill would understand that the temperature and pressure of the produced wet steam is lower than the temperature and pressure of the saturated steam provided to inlet 106 as a function of the thermal transfer that takes place in heat exchange component 104. Preferably, the wet steam exiting heat exchange component 104 has a temperature lower than the temperature of the saturated steam at inlet 106 in a range from 2 degrees C and up to 30 degrees C, including preferably from 5 degrees C and up to 25 degrees C lower, and more preferably from 10 degrees C and up to 20 degrees C lower. Preferably, the wet steam exiting heat exchange component 104 has a pressure in a range from 0.5 MPa and up to 13 MPa, including from 0.5 MPa and up to 13 MPa, preferably from 5.5 MPa and up to 13 MPa, and more preferably from 6.5 MPa and up to 13 MPa.

The second fluid can be provided to second inlet 110 of heat exchange component 104. The wet steam exits heat exchange component 104 in a suitable manner, such as through first outlet 112, and can be used in any suitable application, including being routed to equipment for steam injection in thermal EOR. A wet steam conduit 113 may suitably be provided to receive the wet steam from the first outlet 112 and to route the wet steam.

The steam quality of the produced wet steam may be limited by the content and amount of dissolved solids in the second fluid. Steam quality has the meaning as understood by one of ordinary skill, which is the mass percentage of the fluid that is in vapor phase. Preferably, the steam quality is kept at a predetermined value (minus a safety margin) which is determined by the precipitation point of solids in the second fluid, where by precipitation is avoided. The precipitation point is generally content-specific, and it can be determined by modeling and/or empirically. The predetermined value of steam quality is preferably as high as possible within the bounds of avoiding precipitation.

The quality of the produced wet steam depends at least on the flow rate of the second fluid provided to second inlet 110. For instance, for a particular amount of saturated steam, a higher flow rate of the second liquid produces wet steam with a lower quality as compared to a lower flow rate. The quality of the produced wet steams also depends on the amount of saturated steam provided to heat exchange component 104. For instance, for a particular flow rate of the second liquid, the greater the amount of saturated steam in heat exchanger component 104, the higher the quality of the wet steam produced as compared to a lower amount of saturated steam. The amount of saturated steam provided to heat exchange component 104 depends on a number of factors, one of which is the amount of power supplied to electrode boiler 102. Additional descriptions around the power supply of electrode boiler 102 is further provided in subsequent paragraphs. As such, one of ordinary skill can select operating parameters of the methods and systems described herein to produce wet steam with a steam quality in a range from 10% and up to 99%, preferably from 30% and up to 90%, and most preferably, at least 50%, including from 50% and up to 80%.

The rate at which the second fluid is supplied to heat exchange component 104 depends at least on the operating conditions of electrode boiler 102 to achieve a desired steam quality. As such, for a given power, one of ordinary skill can adjust the second fluid flow rate, or for a given flow rate, one of ordinary skill can adjust the power input to one or more electrode boilers to achieve a desired quality of the wet steam produced in heat exchange component 104.

In heating the second fluid, the saturated steam is partially or completely condensed in heat exchange component 104 through indirect thermal transfer to produce a condensed fluid that exits heat exchange component 104 in a suitable manner, such as through second outlet 114. As used herein, “condensed” or “condensed fluid” means at least partially condensed, including fully condensed, or a fluid that is at least partially condensed (contains both liquid and vapor), including fully condensed (a liquid), respectively and for both as context dictates. Because the saturated steam does not come in direct contact with the second fluid in heat exchange component 104, the electrical conductivity properties of the condensed fluid remains substantially the same as those of the feedwater provided via line 124. As such, at least a portion of the condensed fluid can be recycled back to electrode boiler 102, using a suitable means such as via line 116 and pump 118, for use as part of a portion of the feedwater used to produce the saturated steam. Optionally, substantially most, including all, of the feedwater provided to electrode boiler 102 consists of the condensed fluid that exits heat exchange component 104, such as preferably at least 50%, more preferably at least 75%, and most preferably at least 99% of the feedwater of electrode boiler 102 consists of the condensed fluid. As shown in FIG. 1 , in case the condensed fluid exiting second outlet 114 comprises steam that has not condensed to liquid, prior to returning to electrode boiler 102 as feedwater, the condensed fluid can optionally pass through condensate vessel 120 to separate liquid from uncondensed steam so that liquid is fed to pump 118 for use as the feedwater for electrode boiler 102.

Referring to FIG. 1, electrode boiler 102 is powered by electricity and generates steam from the feedwater by using a number of electrodes that are in contact with the feedwater. Thermal energy is generated by passing an AC electrical current from an electrode to a counter electrode using the water as conductor, and the generated thermal energy heats up the feedwater to generate the saturated steam. Suitable electrode boilers include those described in WO2010095954 and can be operated to produce saturated steam having a pressure in a range from 3.5 MPa and up to 14 MPa, including from

3.5 MPa and up to 14 MPa, preferably from 6.5 MPa and up to 14 MPa, and more preferably from

8.5 MPa and up to 14 MPa. The saturated steam has a corresponding saturated steam temperature in a range from 240 and up to 340 degrees C.

Because electrode boilers are powered by electricity as compared to fossil fuel boilers, they have the following advantages: environmentally friendly with no emissions of products from combustion, close to 100% efficient in converting power to heat with only a minimal percentage of radiation and convection loss from the exposed surfaces of the boiler, easy control of output range and a fast startup, as well as being more compact with smaller volume and footprint for the same capacity than fossil fired boilers. Another type of electric-powered boiler is electric resistance boilers, which uses an electrically resistive element to generate heat, which is transferred to the feedwater, heating it to the desired temperature. While electric resistance boilers have similar advantages as described above for electrode boilers and can be used as described herein, electrode boilers are preferred because they typically have lower costs. Optionally and preferably, electrode boiler 102 has a capacity of at least 5 megawatts (MW), preferably at least 10 MW, more preferably at least 15 MW, which corresponds to a saturated steam production capacity of approximately at least 7 metric tons, preferably at least 15 metric tons, and more preferably at least 23 metric tons of steam per hour. The actual steam production rate generally depends on a number of factors, including the efficiency of the particular electrode boiler used, the power supplied to the electrode boiler and the desired quality of wet steam produced.

Feedwater having an electrical conductivity of less than 200 pS/cm can generally be used with different types of electrode boilers, such as jet electrode or immersed electrode types, as applicable. At less than 200 pS/cm, the feedwater is considered “low-conductivity” and has only a minimal amount of mineral (essentially demineralized water) to control water conductivity to avoid arcing and the current between the electrodes being above suitable operating conditions. Depending on the type of electrode boiler, lower conductivity feedwater may be preferred, such as less than 10 pS/cm, or less than 5 pS/cm.

As described, electrode boiler 102 generates saturated steam having a pressure in a range from 3.5 MPa and up to 14 MPa, including from 3.5 MPa and up to 14 MPa, preferably from 6.5 MPa and up to 14 MPa, and more preferably from 8.5 MPa and up to 14 MPa. The saturated steam has a corresponding saturated steam temperature in a range from 240 and up to 340 degrees C As used herein, saturated steam has its ordinary meaning. In particular, saturated steam occurs when the liquid and gaseous phases of water exist simultaneously at a given temperature and pressure. When heat is applied to water at a particular pressure, the temperature of the water continues to rise until it reaches its boiling point at that pressure. Saturated steam is generated when all of the water (that is, 100%) has reached the boiling point at a particular pressure but has not been heated above that boiling point. As such, saturated steam is in equilibrium with heated water at the same pressure. For instance, saturated steam exists at approximately 100°C (212°F) at atmospheric pressure. Saturated steam is dry, meaning it does not contain any water droplets. If the temperature of saturated steam decreases below the boiling point at a particular pressure, however, the saturated steam no longer exists and reverts back to water. Wet steam occurs when at least some but less than 100% of the water has been converted to steam, meaning wet steam contains droplets of water. Because heat is added to water in electrode boiler 102, saturated steam is the product and not superheated steam which is produced when heat is added to steam.

Although electrode boilers have many advantages to produce steam, one potential challenge is the requirement for low-conductivity water, which can be costly to produce particularly in industrial applications such as thermal EOR, which has typically employed steam production in in a once through fashion using gas-fueled boilers without recycling of the feedwater. Embodiments of the steam production systems and methods described herein address this potential challenge through use of a heat exchanger to transfer the thermal energy from the saturated steam produced by the electrode boilers to heat water of lower quality to generate wet steam. That is, water having an electrical conductivity of more than 200 pS/cm is used as a second fluid that is heated by the saturated steam in heat exchange component 104 to become wet steam. Water with an electrical conductivity of more than 200 pS/cm may be referred to as “lower quality water.”

Because the saturated steam does not come in direct contact with the lower quality water in the embodiments described herein, it maintains the electrical conductivity of less than 200 pS/cm and can continue to be the feedwater for producing saturated steam in the electrode boiler. As such, embodiments of the present systems and methods allow use of electrode boilers to produce steam from lower quality water with minimal need for costly purification systems to replenish the suitable feedwater for such electrode boilers to meet the steam demands in various applications, including industrial applications that typically require steam production at large scale, such as at least 5 MW.

One particularly suitable source of lower quality water to be heated to wet steam for use in thermal EOR is water produced from the well(s) located at the site that is using the thermal EOR to recover hydrocarbons (“produced water”). The proximity of the available water source provides many advantages, particularly cost savings inherent with minimizing the need to transport water from a different location. This source of water for steam production would not be available to electrode boilers unless treated to render it suitable as feedwater, which treatment can be cost prohibitive. This is because the produced water has dissolved solids such as salts, dispersed and dissolved organic content from the hydrocarbons, and a lower pH than suitable feedwater for electrode boilers. These contaminants, such as salts, results in the produced water having an electrical conductivity level higher than the operational specifications for electrode boilers. The dispersed oil can potentially form foam which interferes with level measurements and/or causes a short-circuit.

The systems and methods described herein can produce steam directly from untreated produced water using electrode boilers, even though the option to treat the produced water in some manner prior to being used for steam production is available if desired.

A suitable type of heat exchanger for use as heat exchange component 104 is the shell-and- tube heat exchanger as known to one of ordinary skill. In general, a shell-and-tube heat exchanger includes a shell (usually a large pressure vessel) with a bundle of tubes inside the shell. One fluid runs through the tubes, and another fluid flows over the tubes (through the shell) to transfer heat between the two fluids. The set of tubes is called a tube bundle, and may be composed of several types of tubes: plain, longitudinally finned, etc. Suitably, the lower quality water runs through the tubes while the saturated steam from the electrode boiler flows over the tube through the shell. It is within the skills of one of ordinary skill in the art to select the configurations and operating parameters of the heat exchanger to heat the lower quality water and produce wet steam at a pressure that is sufficiently lower than the saturated steam provided at inlet 108 to enable heat exchange between the two fluids, and quality from 10% and up to 99%. Some exemplary operating parameters include flow rate of the saturated steam, flow rate of the lower quality water, and the operating pressure of the heat exchanger. Other suitable heat exchangers can include hairpin type exchangers.

Electrode boiler 102 may be at least partially or fully powered by various types of renewable electricity as further described in this disclosure. For embodiments in which electrode boiler 102 is powered directly by a renewable electricity source that is not constantly available, the production of saturated steam by electrode boiler 102 can vary corresponding to the power supply, including periods where no power is available to operate electrode boiler 102, which periods can occur frequently. The potentially varying amount of saturated steam entering heat exchange component 104, particularly during potential periods of no saturated steam in heat exchange component 104, in turn, can introduce frequent and/or sudden changes to the operating temperature of heat exchange component 104. Such potential temperature fluctuations can pose a challenge to the mechanical integrity of heat exchange component 104.

One option to address the potential challenge of temperature fluctuations is shown in system 200 of FIG. 2 and system 300 of FIG. 3 in which heat exchange component 104 comprises at least two heat exchangers: first heat exchanger 204A and second heat exchanger 204B. As noted above, when like elements are used in one or more figures, identical reference characters will be used in each figure. For purposes of brevity and ease of reading, a detailed description of the element will be provided only at its first occurrence, which is FIG. 1 in this instance, and not repeated for FIGS. 2 and 3.

Referring to FIGS. 2 and 3, the second fluid is heated in first heat exchanger 204 A to generate a pre-heated second fluid that enters second heat exchanger 204B for conversion to wet steam. Suitably, first heat exchanger 204A is configured to heat the second fluid while maintaining it as a liquid. In each of these embodiments, the second fluid is provided through the second inlet 110A of the first heat exchanger 204A.

Preferably, the second fluid is heated in first heat exchanger 204A to a temperature that is at least 100 degrees C, preferably at least 50 degrees C, more preferably at least 25 degrees C, and most preferably at least 5 degrees C, below the boiling point of water at the operating pressure of first heat exchanger 204A to generate pre-heated second fluid that exits first outlet 112A of first heat exchanger 204A via line 222 and enters second inlet 110B of second heat exchanger 204B. The pre-heated second fluid is then further heated in second heat exchanger 204B to generate wet steam as described above with respect to system 100. As with system 100, the wet steam may be received in wet steam conduit 113.

Suitably, pre-heating the second fluid in first heat exchanger 204A involves less thermal energy than generating wet steam in second heat exchanger 204B. Referring to FIGS. 2 and 3, first heat exchanger 204A is configured to deliver in a range from 30% and up to 45% of the total amount of thermal energy (or heat duty) needed to convert the second fluid to wet steam. F irst heat exchanger 204A has a heat transfer surface area that is less than the heat transfer surface area of second heat exchanger 204B. Suitably, first heat exchanger 204A has a heat transfer surface area that is less than 50%, more preferably less than 30%, and most preferably less than 15%, the heattransfer surface area of second heat exchanger 204B.

FIG. 2 shows system 200 that employs the option of providing saturated steam from electrode boiler 102 to both first and second heat exchangers 204A and 204B in parallel to generate the pre heated second fluid and wet steam as described. In particular, the saturated steam from electrode boiler 102 is provided to first heat exchanger 204A via line 108A and to second heat exchanger 204B via line 108B. Suitably, a range from 30% and up to 45% of the saturated steam from electrode boiler 102 is provided to first heat exchanger 204A via line 108A while the remaining portion of the saturated steam, from 55% to 70%, is provided to second heat exchanger 204B. The amount of steam entering either first heat exchanger 204A or second heat exchanger 204B of system 200 is known to one of ordinary skill. The operating pressure of either heat exchanger 204A or 204B can be set using means known in the art, such as a pressure control valve which can be placed in line 108A or 108B, respectively, or for 204B also through the control of the electrode boiler pressure.

In system 200, the condensed fluid from the saturated steam remaining after the thermal transfer from both first and second heat exchangers 204A and 204B can be provided to individual optional condensate vessels 120A and 120B via lines 214A and 1214B, respectively, to separate liquid from uncondensed steam so that the liquid can be fed to pump 118 for use as feedwater for electrode boiler 102. Optionally, it is understood that the condensed fluid from both exchangers 204A and 204B of system 200 can be collected via lines 214A and 214B and provided to one condensate vessel (not shown) rather than two as shown in FIG. 2.

FIG. 3 shows system 300 that employs the option of providing saturated steam from electrode boiler 102 to first and second heat exchangers 204A and 204B in series. In particular, the saturated steam enters second heat exchanger 204B first from electrode boiler 102 via line 108 to further heat pre-heated second fluid to generate wet steam. The condensed fluid remaining from the saturated steam that exits second heat exchanger 204B is provided to first heat exchanger 204A via line 314 to use the remaining thermal energy in the condensed fluid to pre-heat the second fluid as described here. Cooled liquid remaining from the condensed fluid after the thermal transfer can be routed from first heat exchanger 204 A via line 214 to optional condensate vessel 120, if desired, to separate the liquid from any remaining steam to provide the liquid as feedwater to electrode boiler 102 for use to generate the saturated steam in certain embodiments described herein.

The option of providing saturated steam from electrode boiler 102 to both heat exchangers 204A and 204B in parallel in system 200 provides a greater degree of control over the temperature of the pre-heated second fluid exiting first heat exchanger 204 A as compared to system 300, such as by setting the operating pressure of either heat exchanger 204A. In system 300, the temperature of the pre-heated second fluid exiting first heat exchanger 204A can be influenced by configuring the size of the heat transfer surface area of heat exchangers 204 A.

The impact of the potential temperature fluctuations noted above is minimal for first heat exchanger 204A with its relatively smaller size while it provides a temperature buffer for second heat exchanger 204B. The preheated lower quality water input to second heat exchanger 204B enables it to be operated at more constant temperatures, thereby decreasing the impact of the potential temperature fluctuations, which impact can be particularly challenging from a mechanical integrity perspective under the operating conditions as described in this disclosure.

In each of the systems of Figs. 2 and 3, the wet steam discharged from the first outlet 112B of second heat exchanger 204B may be routed to equipment for steam injection in thermal EOR. Each of these systems may thus be comprised in a thermal EOR system. Such thermal EOR system may further comprise a wet steam injection line into a subsurface hydrocarbon formation to which the system described herein is functionally connected.

At least a portion and preferably all components of the steam production systems and methods described herein are powered by electricity. The source of electricity can come from a typical electrical power grid if access is available to the site of operation. In large-scale steam production, such as those employed for thermal EOR, the power requirement can be significant, and the site of operation may be remote so grid access may not be economically feasible or practical.

The present disclosure provides for the option to use renewable electricity to address some of the foregoing challenges as well as allow for generation of “green” steam for use in thermal EOR. Such renewable electricity includes wind and solar energy. Use of such renewable resources for generating electricity releases less emissions than the combustion of fossil fuels. The benefits of reducing emissions from steam generation include collecting carbon credits and meeting carbon reduction goals currently being set by many governments and corporations. In addition, through the use of an islanded grid, an embodiment of the steam production system can optionally be “utility -grid-in dependent’ ’, meaning that the power needed to operate the system to generate steam, including the power needed to operate the electrode boiler(s), pumps, valves, other ancillary components, etc., does not come from a conventional electrical utility grid and that no electrical connection is present between the islanded grid and the electrical utility grid. FIGS. 1 and 2 illustrate systems 100 and 200, respectively, with islanded grid 126. One suitable option for islanded grid 126 is a solar photovoltaic (PV) grid which comprises a multitude of interconnected photovoltaic cells (not shown). Another suitable option for grid 126 is an islanded wind grid. It is within the knowledge of one of ordinary skill to select the size or energy production capacity of the selected islanded grid based on the maximum power demand of the electrode boilers and any additional auxiliary equipment, local weather data, expected transmission losses, and any combination thereof. The electricity produced by islanded grid 126 is provided at least to electrode boiler 102, such as via line 128. Optionally, it can also be provided to other ancillary equipment to systems 100 or 200, and/or other nearby equipment (not shown).

Islanded grid 126 being utility-grid-independent is beneficial for remote locations at which electrical utility infrastructures may be limited, and as well for generating carbon credits in some cases. Additionally, being utility-grid-independent can reduce costs and time to steam production by avoiding the need for interconnection agreements that can add schedule delays and charges associated with utility infrastructures.

Optionally, certain embodiments of the steam production systems and methods described in this disclosure can be designed to run intermittently rather than on a continuous basis. This is particularly applicable if such embodiments are powered by renewable sources such as wind or solar PV that are not constant. As such, certain embodiments can be optionally designed to supplement existing steam production equipment, such as OTSG and HRSG, thereby allowing carbon offsets in oil and gas operations by using renewable energies in the hydrocarbon recovery processes.

While the descriptions and FIG. 1 may show one electrode boiler and one heat exchanger, it is understood that any number of electrode boilers and heat exchangers can be used (such as two or more) to meet the desired specifications, such as the total quantity of wet steam output. The selection of capacity, number, and type of electrode boilers and heat exchangers, as well as pump configurations and other ancillary equipment to achieve desired specifications, are within the design choices known to one of ordinary skill. Accordingly, referring to FIG. 1, the present disclosure provides a method for generating wet steam, the method comprises providing feedwater having an electrical conductivity of less than 200 pS/cm to electrode boiler 102, which has a capacity of at least 5 MW, and converting the feedwater to saturated steam by electrode boiler 102. The saturated steam has a pressure in a range from 3.5 MPa and up to 14 MPa and a temperature in a range from 240 degrees C and up to 340 degrees C. The method further comprises providing at least a portion of, and including up to all of, the saturated steam as a first fluid to first inlet 106 of heat exchange component 104 via line 108; and providing water having an electrical conductivity of more than 200 pS/cm as a second fluid to heat exchange component 104 via second inlet 110. The second fluid is heated in heat exchange component 104 through indirect thermal transfer with the saturated steam to generate wet steam having a temperature lower than the temperature of the saturated steam by a range from 2 degrees C and up to 30 degrees C and a pressure in a range from at least 0.5 MPa and up to 13 MPa. The saturated steam is cooled in the heat exchanger through indirect thermal transfer with the second fluid to produce a condensed fluid. At least a portion of the condensed fluid is provided to electrode boiler 102, such as via line 116, for use as part of the low-conductivity water to generate said saturated steam. It is understood that the optional ranges of temperatures and pressures described above and elsewhere are equally applicable in this paragraph and throughout this description as context dictates and is not repeated here for purposes of brevity and ease of reading.

Suitably, at least 50%, preferably at least 75%, or more preferably at least 99% of the condensed fluid is provided to electrode boiler 102 for use to generate said saturated steam.

Optionally, referring to FIG. 2, heat exchange component 104 comprises first heat exchanger 204 A and second heat exchanger 204B. The step of providing the saturated steam to heat exchange component 104 preferably comprises providing a first portion of the saturated steam to first heat exchanger 204A, providing the second fluid to first heat exchanger 204A, and heating the second fluid in first heat exchanger 204A through indirect thermal transfer with the first portion of the saturated steam to generate a pre-heated second fluid. The pre-heated second fluid and a second portion of the saturated steam are provided to second heat exchanger 204B. The step further comprises heating the pre-heated second fluid in second heat exchanger 204B through indirect thermal transfer with the second portion of the saturated steam to generate the wet steam. Preferably, first heat exchanger 204A provides from 30% and up to 45% of the total thermal energy needed to convert the second fluid to wet steam. Optionally, referring to FIG. 3, heat exchange component 104 comprises first heat exchanger 204 A and second heat exchanger 204B. The step of providing the saturated steam to heat exchange component 104 preferably comprises providing the second fluid to first heat exchanger 204A and heating the second fluid in first heat exchanger 204A through indirect thermal transfer with a condensed fluid from second heat exchanger 204B, provided via line 314, to generate a pre-heated second fluid. The step further comprises providing the pre-heated second fluid to second heat exchanger 204B via line 222 and providing the saturated steam to second heat exchanger 204B via line 108. The step further comprises heating the pre-heated second fluid in second heat exchanger 204B through indirect thermal transfer with the saturated steam to generate the wet steam; and at least partially condensing the saturated steam in second heat exchanger 204B through indirect thermal transfer with the pre-heated second fluid to produce the condensed fluid that is provided to first heat exchanger 204A to generate the pre-heated second fluid.

Optionally, at least a portion of the wet steam exits first outlet 112 of heat exchange component 104 for injection into a subsurface hydrocarbon formation for hydrocarbon recovery. Electricity powering the operation of electrode boiler 102 can optionally comprise green energy, including but not limited to solar photovoltaic panels, wind turbines, hydropower, a battery charged with any one or more of the foregoing, and any combination thereof, which can be delivered via line 128. Optionally, at least a portion of the electricity is generated by one or more solar photovoltaic panels. Electrode boiler can be powered completely by green energy produced by a power source that is not connected to an electric grid, such as an islanded solar PV microgrid. The green energy can be provided for use by the hydrocarbon recovery site.

As described, the present disclosure provides systems and methods to produce steam that address various challenges noted above. The generated wet steam is primarily intended for thermal EOR, but other uses may be contemplated.