Patent Description:
Oil reservoirs are geological units within the subsurface of the Earth that contain an accumulation of oil. The oil from the reservoirs is extracted or recovered for use by a process commonly referred to as oil production. Conventional oil production typically involves two stages: primary recovery and secondary recovery. Primary recovery involves the use of natural in-reservoir high pressure forces to drive the flow of oil to oil production wells. Secondary recovery typically involves the maintenance of this high pressure by pumping fluids into the reservoir so that oil production may continue.

In oil reservoirs that contain heavy oil or oil-sands (also known as tar sands, bitumen, or bituminous sands), the oil is too viscous to flow freely to the production wells by conventional methods. As such, other means of oil production, such as thermal recovery strategies, must be employed. Thermal recovery strategies involve heating the oil reservoirs to improve the mobility of the oil and thus the ease of its subsequent extraction. The applied heat reduces the oil's viscosity allowing it to flow to production wells. An example of a commonly used thermal recovery strategy in heavy oil recovery is the Steam-Assisted Gravity Drainage (SAGD) method.

The SAGD method involves the use of steam injection well <NUM> and production well <NUM> pairs, as depicted in <FIG> of the prior art. The steam injection well introduces steam into a clean sand area <NUM> of an oil reservoir. The injected steam migrates upwards until reaching geological units that prevent further migration of the steam. The injected steam heats the reservoir to temperatures of approximately <NUM>, reducing the viscosity of the oil and allowing it to flow to the oil production wells. This is referred to as the steam chamber <NUM>, shown in <FIG>. The steam is constantly injected to provide pressure to facilitate the continuous flow of oil towards the production wells, and to help displace the oil from the sand.

There are several drawbacks to the SAGD process. One major issue is that the SAGD steam-generation process has a negative environmental impact. For example, the SAGD process is a large contributor of greenhouse gas emissions. This is because large amounts of natural gas must be combusted to provide the energy to heat the fresh water to create the steam. Not only does burning natural gas contribute significantly to greenhouse gas emissions, it also represents an added cost for bitumen production. Furthermore, the SAGD process also consumes large amounts of fresh water resources for the creation of the steam.

As the production of steam is the primary contributor to the environmental and economic impact of the SAGD method, the environmental efficiency of SAGD operations may be expressed in terms of the steam-to-oil ratio (Gates & Larter, <NUM>). The steam-to-oil ratio encompasses both the environmental and economic cost of steam generation in relation to the amount of crude oil resource that is recovered. A lower steam-to-oil ratio means fewer greenhouse gas emissions and improved environmental performance per unit of production.

The energy costs and greenhouse gas emissions associated with unconventional oil sands extraction and production, such as SAGD operations, are approximately <NUM>-<NUM>% greater than for conventional oil production ("<NPL>,). As such, new strategies and technologies for improving the environmental and economic performance in oil sands extraction must be developed to lower the steam-to-oil ratio associated with SAGD operations.

Production from conventional oil reservoirs is typically inefficient at extracting all of the available oil from the targeted region. As such, there are many strategies that aim to increase oil recovery. Some of these strategies include the use of microorganisms in the subsurface.

Subsurface environments are microbial habitats and include a wide variety of microbial taxa. <FIG> of the prior art shows a histogram of the abundance rank order of different microbial taxa in a subsurface environmental sample; adapted from <NPL>. The bars of the histogram are indistinguishable as they are very close together. The lighter shaded area <NUM> on the left of the histogram represents abundant taxa, and the darker shaded area <NUM> to the right represents the rare taxa. Therefore, in a given environmental sample, there is often a large proportion of abundant and active microorganisms along with a variety of low abundance, inactive and/or dormant microorganisms. For example, in some microbial communities, one species might encompass up to <NUM>% of the total cells present, whereas hundreds of rare species may collectively make up less than <NUM>% of the total.

Microbially Enhanced Oil Recovery (MEOR) is a term to describe strategies for conventional oil production that target the use of microbial communities for enhancing and increasing oil recovery from conventional oil reservoirs. MEOR is typically employed after primary and secondary recovery. With MEOR, microbes are utilized in the conventional target regions of the reservoir to improve oil production. MEOR is believed to occur by a variety of mechanisms related to microbial metabolism in oil reservoirs, including biosurfactant production, metabolism of oil, and production of gas as a metabolic by-product. Each of the processes mentioned above helps to increase the fluid mobility of the oil, leading to the production of the residual oil still present the reservoir after primary and secondary recovery strategies.

MEOR is typically attempted as a tertiary recovery strategy in conventional oil reservoirs. However, due to the unconventional nature of heavy oil sands bitumen, and the unconventional production methods for producing this oil, MEOR strategies are not frequently applied in heavy oil sands.

MEOR may be applied to the commonly-targeted region of a heavy oil or bitumen unit before or after the application of strategies such as the SAGD method. MEOR involves either (<NUM>) biostimulation, i.e., the injection of nutrients to stimulate the native predominant and abundant taxa, or (<NUM>) bioaugmentation, i.e., the injection of foreign bacteria that are thought to be suitable for the reservoir conditions.

The high temperature of the SAGD steam chamber sterilizes the conventional target region of the oil sands reservoir. Therefore, when MEOR is utilized for enhancing oil recovery from the SAGD steam chamber of a heavy oil sands reservoir, MEOR may only be applied either before the steam is injected into the reservoir, or after the SAGD method is complete and the reservoir has cooled down to low temperatures. <CIT>, describes a method of injecting foreign bacteria prior to injecting steam as a part of SAGD for increasing the fluid mobility of oil in a heavy oil reservoir. In this method, microorganisms are introduced into the reservoir through both injection and production wells, prior to steam injection, to pre-condition the reservoir for enhanced (shorter) start up of the SAGD process.

<CIT>, provides an example of biostimulation in a conventional oil reservoir in conjunction with waterflood technology. Waterflooding aims at displacing the residual oil in the reservoir with water, rather than the steam that is applied during the SAGD method. Similarly, <CIT>, and <CIT>, describe methods involving the injection of nutrients in the conventional oil reservoirs for enhancing oil recovery.

All of these methods, however, focus on the active taxa present in high relative abundance in the microbial communities that are adapted to local prevailing in situ conditions (temperature, geochemistry, salinity, mineralogy, etc.) and that are readily investigated by microbiological methods. Yet, in nearly every environment there are microbial seed banks that include many species or taxa of microorganisms present in very low relative abundance. These microbial taxa can be inactive or dormant, and may include dormant bacterial endospores. Microbial seed banks may constitute significantly less than <NUM>% of the total cells present, and often exist in a dormant state. As such, they are typically not detected or highlighted by most environmental DNA extraction surveys, and other more traditional methods for microbial characterization of oil reservoir environments.

Furthermore, the subsurface regions beyond the boundaries of the SAGD steam chamber, such as inclined heterolithic strata (IHS), may contain up to twice as much oil sands resource as the targeted steam chamber region. However, production of the oil in the IHS region during SAGD is negligible. This IHS oil is mixed with sand, and interbedded with thin, but laterally extensive, low-permeability mudstone layers through which the steam cannot penetrate. Therefore, the steam pressure driving mechanism required to displace the oil is not provided. The oil in the IHS is considered higher quality and more valuable than the oil in the steam chamber region as it is less biodegraded and less viscous ("<NPL>.

<FIG> shows a schematic of an example of a commonly-targeted geological unit in the subsurface of the Athabasca oil sands. The lower region represents the target for steam chamber <NUM> placement, which is the targeted region for SAGD. The upper region represents the IHS region <NUM>, which contains oil that is not easily accessible by current methods. Limited oil recovery is documented from the IHS. The diagonal lines in the IHS region represent the laterally extensive mud strata <NUM> interbedded with decimeter scale heavy oil or bitumen saturated laterally extensive porous sands. Above and below these regions are the low-permeability non-reservoir underseal <NUM> and seal <NUM>.

<FIG> shows a photograph of an Athabasca Oil Sands outcrop near Fort McMurray in Alberta, Canada by <NPL>. The geological unit shown in <FIG> is representative of the geological unit in the Athabasca Oil Sands. Referring back to <FIG>, the white substantially parallel lines along the upper half of the geological unit represent the laterally extensive mud strata <NUM> of the IHS region <NUM>, and have a slope of approximately six (<NUM>) to ten (<NUM>) degrees. The lowest laterally extensive mudstone layer <NUM>, as denoted by the arrow, defines the expected upper boundary of the SAGD steam chamber <NUM> (as demonstrated by subsurface studies, Strobl et al. , <NUM>, Strobl, <NUM>).

The oil in the IHS is generally considered to be trapped and inaccessible. While means to increase oil recovery from the accessible regions, such as the SAGD steam chamber, are widely researched, access to the oil in the IHS layer remains challenging with use of existing technologies. There are many initiatives to try to access this oil, such as by attempting to break the mudstone in the IHS by geomechanical, electrical, Enhanced Solvent Extraction Incorporating Electromagnetic Heating (ESEIEH), or thermo-chemical processes to access the oil. However, these approaches have had a very limited success thus far.

<CIT> discloses a method of enhancing heavy oil recovery from a reservoir through the injection of a microorganism capable of digesting oil, and subsequently recovering oil from the reservoir.

There is therefore a need to mitigate, if not overcome, the shortcomings of the prior art and to, preferably, develop a method to produce oil or increase oil production from currently challenging IHS regions of oil reservoirs.

The present invention is defined by independent claim <NUM>, other embodiments, aspects and details according to the present invention will become apparent by the accompanying dependent claims. Nutrient and thermal enhancement of microorganisms in oil containing geological units allows for stimulation of inactive and/or dormant microorganisms such that they proliferate and produce gas. The oil viscosity that is decreased by heat, along with the gas pressure produced by activated microbes which increases oil mobility, allows previously inaccessible oil to flow toward production wells.

The present publication describes how to utilize the conductive heat generated by SAGD, combined with nutrient injection, to enable the production of oil trapped in geological strata such as the IHS. When used in conjunction with SAGD technology, the method and system described herein may be referred to as a Microbially influenced SAGD (MiSAGD) method or system.

It is another aim of the present invention to access heavy oil that is not accessible by either conventional oil production methods or SAGD, such as in oil-containing units less than <NUM> meters thick. These thin sediment layers may be thermally treated with warm water (up to <NUM>) to reduce viscosity, as well as nutrients for microbial enhancement (e.g. of dormant thermophiles), to facilitate the production of oil. In such circumstances, the method described herein may be referred to as a Microbially Enhanced Thermal Oil Recovery (METeOR) method.

A method for oil recovery in a subsurface oil reservoir is described herein as defined in claim <NUM>.

The embodiments of the present invention will now be described by reference to the following figures, in which identical reference numerals in different figures indicate identical elements and in which:.

The Figures are not to scale and some features may be exaggerated or minimized to show details of particular elements while related elements may have been eliminated to prevent obscuring novel aspects.

This document refers to oil as a generic term. However, the term oil may be used interchangeably with the terms heavy oil, extra-heavy oil, natural bitumen, tar-sands, oil-sands, bituminous sands or petroleum. The present invention provides a method to recover oil from inaccessible oil-containing geological units by activating the existing microbial seed bank present in situ. By providing nutrients and heat to inactive, dormant, microorganisms, including bacterial endospores, that are situated in oil containing geological units, the microorganisms may proliferate and produce gas for enhanced oil recovery via enhanced pressurization and/or oil mobility. The supplied heat that further lowers the viscosity of the oil, along with the gas pressure produced by the activated microbial communities that were formerly inactive or dormant, along with increased mobility of oil due to the increased presence of gas, combine to allow the previously inaccessible oil to flow toward an oil production well.

Microorganisms with thermal limits for growth that are higher than the prevailing in situ temperature are known to exist in sediments, as shown in <FIG> and <FIG>, and described further in this document. These microorganisms typically exist as part of the inactive or dormant seed bank unless or until environmental conditions change, e.g., by heating or through the provision of nutrients. Prior to SAGD, a typical oil sands reservoir and overlying IHS will be approximately <NUM> in situ.

As the oil of the IHS and other inaccessible regions are considered trapped and inaccessible due to the extensive nature of low-permeability mudstone layers, there are not currently any technologies that effectively recover oil from IHS layers.

In one embodiment, the present invention utilizes the conductive heat generated by existing thermal recovery methods such as SAGD. Although the high <NUM> temperatures of the injected steam effectively sterilize the steam chamber region itself, the steam cannot penetrate the dense interbedded sand and mud of the IHS. Therefore, while the <NUM> steam chamber is sterilized, the surrounding areas of the subsurface are not necessarily sterilized because they experience a lower temperature. The present invention utilizes the heat from the injected steam, which conductively flows through both the mudstone and the oil-saturated sand strata of the IHS region in contact with the SAGD chamber. This creates a temperature gradient from the edge of the hot steam chamber (~<NUM>) to regions that are at ambient temperature (~<NUM>).

For example, for a SAGD steam chamber that is ~<NUM> metres below the subsurface, the temperature gradient due to heat conduction will extend upward tens of metres until an elevation where the ambient subsurface temperature does not change. As such, a large portion of the IHS will have temperatures that are much higher than prior in situ temperatures (<<NUM>) but below what is understood to be the upper temperature limit for microbial life (~<NUM>). These temperatures are favourable conditions for activating dormant members of the microbial seed bank, such as endospores of thermophilic bacteria that germinate and grow in response to the increase in temperature.

Furthermore, in this embodiment, given that the sediments and oil of the IHS are heated without additional input, the associated CO<NUM> greenhouse gas emissions and energy costs associated with oil production from a given operation do not necessarily increase. Hence the overall greenhouse gas emissions per barrel of oil decrease and the steam-to-oil ratio may decrease.

The conductive heat also reduces the viscosity of the oil, and mobilizes the oil that is otherwise inaccessible to steam in the regions beyond and/or above the steam chambers. However, although the heated oil in the IHS has a reduced viscosity to such a low level that it can flow, around 10cP, there is no pressure to drive it through the lowermost laterally extensive mud layers into the SAGD steam chamber where the production well is located (see <FIG>).

In another embodiment, the present invention promotes gas production by the microorganisms in the IHS. The gas production in turn increases oil mobility and provides a pressure drive to produce the oil.

The proliferation of these microbial seed bank microorganisms is enhanced by optimizing environmental conditions for a given group or groups of microbes. This optimization may be provided by nutrient and/or injection of microbial cells into the IHS. In one aspect, the gas produced by the proliferating microbes provides pressure to drive the oil to a production well through the oil saturated intervals sandwiched between the laterally extensive, slightly inclined (often between <NUM> and <NUM> degrees) mud layers.

<FIG> shows a bar graph representing bacterial metabolism for sediment samples from the Arctic Ocean seabed under various nutrient and temperature conditions. This graph is adapted from <NPL> combined with unpublished data. The analyzed samples are representative of sediments from permanently cold (~<NUM>) subsurface regions. As such, these samples include heterogeneous microbial communities including many strains. The samples were incubated for <NUM> days under four sets of conditions:.

Microbial metabolism, a measure of microbial proliferation, was determined by measuring sulphate reduction in the experiments. At in situ temperature (~<NUM>) and without nutrients, minimal microbial metabolism or activity is observed. Therefore, the thermophilic microorganisms in the sample may be considered dormant at in situ temperature. When the temperature was raised to <NUM>, metabolism by thermophilic microorganisms became apparent, indicating a temperature dependent activation of dormant bacterial endospores.

Still referring to <FIG>, the addition of simple nutrients at <NUM> enhanced microbial metabolism up to two fold, and up to four fold with more complex nutrients. Therefore, the activation of dormant sediment microorganisms may be fostered and increased by the addition of heat and nutrients, with more complex nutrients providing an environment significantly more conducive to growth and metabolism. <FIG> shows the three <NUM> groups presented in <FIG> as a line graph showing microbial metabolism over time. In addition to the relative proliferation of the microorganisms under different conditions, this graph further shows that the dormant microorganisms are activated up to <NUM> hours sooner when enriched with nutrients.

The type of gas produced by the microorganisms depends on the prevailing conditions, such as available nutrients, as well as the specific organisms of interest. Therefore, the gases produced include, but are not limited to, carbon dioxide, methane, nitrogen, ammonia, hydrogen and hydrogen sulfide.

Referring to <FIG>, presented is a line graph tracking bacterial metabolism for sediment samples from an oil sands reservoir incubated at 50C. This graph tracks anaerobic bacterial metabolism as a function of time in oil sands samples incubated at 50C in the presence of nutrients or with no nutrient amendment. Two depths from the same oil sands reservoir were tested, and the average from replicate experimental bottles for each condition is shown. The experiment is similar to the incubations shown in <FIG> and <FIG>, and demonstrates that dormant thermophiles can be activated in oil sands that experience high temperature. Nutrient amendment was required in order to stimulate anaerobic metabolism by thermophiles in the oil sands samples. These oil sands were obtained from frozen cores that were drilled prior to SAGD such that the only heating took place in the experiments. Two depths (ca. <NUM> and <NUM> below surface) were tested, each in triplicate. Unamended controls for each depth were tested in duplicate.

<FIG>, and <FIG> show a a long horizontal nutrient injection well <NUM> drilled into the IHS region <NUM> above the SAGD steam chamber <NUM>. In the embodiment shown in <FIG>, gas <NUM> may be generated by microbes that are activated in response to the conductively heated IHS layers. In the embodiment shown in <FIG>, nutrients <NUM> are injected from a tank <NUM> on the surface. The injected nutrients <NUM> are incubated in the conductively heated IHS region <NUM> during SAGD, occurring in the steam chamber <NUM> below. Dormant microorganisms <NUM> that may be activated by the conductive heat as shown in <FIG>, are further activated and enhanced by the injected nutrients <NUM>, to produce gas <NUM>. In one embodiment, the gas <NUM> produced by the activated thermophilic microbes <NUM> improves oil mobility and/or provides pressure for oil lying between the laterally extensive mud strata <NUM> to flow downwards along the inclined mud strata into the steam chamber <NUM> below for oil production.

The microbial gas production is enhanced by determining and utilizing optimal nutrient formulations and temperature conditions to promote maximum microbial activation and proliferation. Nutrient formulations with the present invention are designed based on either (<NUM>) specialized knowledge of the microbial seed bank and anaerobic microbial metabolism, or (<NUM>) formulations based on the specific microbial community present in a given reservoir. The latter formulations may be prepared by site-specific pre-characterization lab testing of the microbial seed bank of a given IHS region using samples taken from that IHS region. The pre-characterization may include studies on how best to stimulate the particular seed bank at different anticipated temperatures. The samples of IHS sediments would typically be available from drill cores taken during an exploration survey of the subsurface, or during the process of drilling the SAGD injector-producer well pairs.

The nutrient formulations may include growth substrates that are carbon-based organic compounds, nitrogen and phosphorous compounds, metal compounds, vitamins, or different electron acceptors like oxygen, nitrate, metal oxides and sulfates. The nutrient formulations may be specialized and site-specific as described above, or may be standardly applied based on specialized knowledge of general physiology of anaerobic microbial consortia capable of gas production.

In one embodiment, the present invention aims at driving the oil towards the steam chamber along the gentle inclination of the laterally extensive mud strata rather than attempting to break down the mudstone boundary of the steam chamber as in existing techniques. As such, in some embodiments, the present invention utilizes existing oil production wells <NUM>, for example as shown in <FIG>, to produce the oil from the IHS region. Additional production wells can be drilled into the IHS region.

An advantage of some embodiments of the present invention includes a reduction in oil production costs per barrel of oil produced relative to the traditional SAGD method, because the costs associated with nutrient injection are likely lower than those of steam generation. As such, embodiments of the present invention will yield a considerable increase in oil production with only an incremental cost increase for additional nutrient wells, and without any change of the SAGD method.

A further advantage of embodiments of the present invention is that it seeks to decrease the steam-to-oil ratio. Therefore, with the same amount of steam in the traditional SAGD method, embodiments of the present invention allow for a significantly larger amount of oil to be produced, and thereby may reduce the relative amount of greenhouse gas emissions per unit of oil production.

Additionally, as the oil in the IHS region is less biodegraded and viscous than that of the steam chamber, it is more commercially valuable. Further, the decreased viscosity requires less energy to flow through the oil production wells.

Furthermore, when heated, the less-biodegraded oil of the IHS region is amenable to supporting the gas-producing microbial activity if it can still be further biodegraded. As such, in some embodiments of the present invention, the oil naturally present in the IHS region may contribute as a form of nutrients for microbial growth.

In another embodiment of the present invention, microbial cells may be injected in the IHS region as a form of bioaugmentation. Site specific lab testing is required to determine ideal nutrient and/or bioaugmentation formulations. The injected cell stocks may originate from seed bank microorganisms isolated and cultured from corresponding reservoir core samples. Alternatively the injected cells may be standard microbial species or consortia known to produce gas under high temperature anoxic conditions.

In some embodiments of the present invention, it may be desirable to access a large portion of the IHS region. As such, the present invention contemplates embodiments including more than one nutrient injection well. The nutrient injection wells may be drilled with different widths, depths (shallow or deep), horizontally, directionally, and/or vertically depending on the targeted area for nutrient injection. The decision to drill fewer or more nutrient injection wells, or horizontal and/or vertical wells, may be determined based on the characteristics of a particular site and calculated cost/benefit ratios.

Horizontal wells may be used to target the stimulation of particular areas in the geological unit based on temperature or microbiological conditions. In another alternative, the horizontal wells may be similar to the horizontal SAGD wells. The horizontal wells may also be up to <NUM> long or longer horizontally and/or access the entire oil reservoir area.

The nutrient injection wells may be drilled from the same surface location or infrastructure as existing production wells, such as the SAGD production well pads. Therefore, in such embodiments where the technology is employed in conjunction with another oil recovery method such as the SAGD method, these additional wells are likely to represent a smaller incremental deployment cost.

In an alternative the method described herein may be utilized in a normally inaccessible zone such as the IHS region before or after the SAGD method. The heat generated from thermal oil-recovery strategies such as the SAGD method is only accessible while the SAGD method is active and ongoing. Therefore, when the present invention is utilized before or after the SAGD method, warm water may be injected as a thermal enhancement to maintain optimal temperature conditions for microbial seed bank activation, microbial proliferation and gas production. The warm water may be injected continuously or periodically. In some embodiments of the present invention, the warm water may be injected with nutrients and/or microbes.

In one embodiment, the warm water may be injected during the SAGD method to supplement the heat of a particular region of the IHS.

In another embodiment, the method described herein may involve site-specific local surveillance testing and preparations for enhanced oil recovery, including:.

The present invention includes a method for recovering oil from an oil reservoir in the subsurface of the Earth. In this method, an injection well is provided in the subsurface for injecting at least one nutrient. A heat source is provided to continuously heat the subsurface, before during or after the injection of the at least one nutrient. The gas-producing microorganisms located in the subsurface are incubated for producing gas pressure which drives the oil to the production well for recovery.

The injection, incubation and production steps outlined above may be repeated cyclically. In another alternative, the oil production may be concurrently performed with the incubation of the microbes with injected nutrients.

In a further embodiment, the present invention may be applied to microbial seed bank organisms in subsurface heavy oil reservoirs that are currently not accessible by, or attractive for, conventional and/or thermal recovery (i.e. SAGD) methods, such as relatively thin layers of oil-saturated sand e.g. that are less than <NUM> meters thick. In such thin reservoir zones, the SAGD method is not generally employed as it is considered to be not economically justifiable. In this embodiment, as the thermal energy cannot be obtained from a concurrent thermal strategy such as the SAGD method, the thermal energy must be introduced to the sediment by another means.

In one embodiment of the present invention, thermal energy may be provided to the target area by the injection of warm water as previously mentioned. <FIG> shows the first phase of such an embodiment. A nutrient injection well <NUM> injects warm water, nutrients, and optionally, microbes <NUM> from a tank <NUM> above the surface. In one embodiment of the present invention, the warm water, nutrients, and optional microbes <NUM> are steadily flowed into the oil reservoir <NUM> to reduce viscosity by heat and activate and incubate the microbial community, including the dormant seed bank, for it to produce gas that enhances oil mobility and/or provides pressure drive for oil production.

<FIG> shows one embodiment of the second phase of the embodiment of the present invention shown in <FIG>. In this embodiment, the nutrient injection well <NUM> may also serve the function of a production well. The heated and therefore less viscous oil is driven by the gas produced by the microorganisms in Phase One (<FIG>) toward the well for production (<FIG>).

The temperature of the warm water may vary depending on the targeted microbial community's preferences. The warm water heats the sediments, and along with the nutrients, reduces the viscosity of the oil, and may contribute to pressurizing the reservoir. Thus, the high temperature-adapted microbes are activated and proliferate to produce gas that increases in situ pressure and/or oil mobility, leading to enhanced flow and oil production.

In one embodiment of the present invention, the warm water may be injected to facilitate oil production, and the injection/production cycle continues to be repeated. In some embodiments, the period of injection/production cycles may be reservoir specific and may be determined by prior attempts at conventional cold temperature oil production.

In one embodiment of the present invention, such alternating cycles may continue until oil production ceases. In another alternative, the incubation of the microorganisms in the subsurface sediments with warm water and nutrients may last beyond several months. In a further alternative, the oil production may last up to <NUM> months and beyond.

The nutrient injection wells and/or warm water injection may also be used for oil production.

The supplemental thermal energy provided by warm water may be used to supplement primary cold temperature oil production or secondary oil production such as waterflood technology.

Claim 1:
A method for oil recovery in a subsurface of an oil reservoir, the method comprising steps of:
(a) providing at least one injection well within the subsurface;
(b) providing a heat source to continuously heat the subsurface;
(c) injecting at least one nutrient into the subsurface through the at least one injection well, the at least one nutrient being based on either specialized knowledge of a microbial seed bank and anaerobic microbial metabolism or presence of a specific microbial community present in a given reservoir;
(d) stimulating activity of at least one gas-producing in situ dormant microorganism from an existing microbial seed bank present in situ located in the subsurface to produce a gas pressure; and
(e) recovering oil through a production recovery well.