Methods of Recovering Oil from Rock Formations

This disclosure relates to methods of recovering oil from a rock formation, such as by utilizing heat and carbonated water to mobilize the oil within the formation.

Enhanced oil recovery (EOR) involves injecting a substance into a formation (e.g., flooding the formation with the substance) to displace oil contained within the formation toward a producing well. In some instances, the injected substance creates favorable conditions in the formation for recovering the oil, such as oil swelling, oil viscosity reduction, and wettability alteration. The ultimate goal of any EOR process is to reduce residual oil saturation within the formation, which is controlled by interactions at the pore scale of the formation. In some cases, carbonated water is used as an injected substance for EOR. One challenging aspect of using carbonated water is that it is denser than reservoir fluids. This relatively high density can lead to gravity underride problems, which result in displacement of oil within lower zones of a formation, while undesirably leaving oil in upper zones of the formation untouched (e.g., thereby failing to displace such oil in the upper zones).

This disclosure relates to a process for recovering oil from a rock formation. The process involves placement of downhole heaters within one or more wellbores to generate heat within a region of the formation where carbonated water has been provided. The generated heat causes carbon dioxide (CO2) gas to be released from the carbonated water. The released CO2 gas moves into an upper zone of the formation, where the released CO2 gas interacts with oil contained in the upper zone. For example, the released CO2 gas mobilizes the oil to enhance recovery of the oil during an oil recovery operation.

The details of one or more embodiments are set forth in the accompanying drawings and description. Other features, aspects, and advantages of the embodiments will become apparent from the description, drawings, and claims.

illustrates an example rock formationprior to an oil recovery operation to recover oilfrom the formation. A first wellboreis located in a first region(e.g., at a first side) of the formation, and a second wellboreis located in a second, opposite region(e.g., at a second side) of the formation. The wellboreis equipped with a first production tube, while the wellboreis equipped with a second production tube.

Referring to, in a first phase (e.g., a water flooding phase) of an oil recovery operation to recover oil from the formation, wateris introduced (e.g., injected) into the formationthrough lateral openingsin the production tube. The waterflows into an annular region (not shown) defined between the production tubeand the wellboreand, from the annular region, flows (e.g., permeates) into the formationthrough pores along the wellbore. The watersubsequently flows (e.g., spreads) laterally from the first regionof the formationto the second regionof the formation(e.g., towards the wellbore). In some examples, the wateris delivered to the formationover a period of several months to several years until one or both of the wellbores,produce mostly water (e.g., about 90% to about 100% water of the produced fluid).

Referring to, in a next phase of the oil recovery operation (e.g., a carbonated water flooding phase), carbonated wateris introduced (e.g., injected) into the formationthrough the lateral openingsof the production tubeand the annular region. In some examples, the carbonated water is produced by mixing carbon dioxide (CO2) gas and water prior to the injection (e.g., either at the surface or within injection tubing). The carbonated wateralso flows (e.g., spreads) laterally from the first regionof the formationto the second regionof the formation. As the carbonated waterflows across the formation, the carbonated watermixes with the waterto form carbonated waterof somewhat reduced (e.g., diluted) carbon dioxide concentration. In some examples, the carbonated wateris delivered to the formationover a period of several months to several years until one or both of the wellbores,produce mostly carbonated water (e.g., about 90% to about 100% carbonated water of the produced fluid).

Referring to, in a next phase of the oil recovery operation (e.g., a heating phase), one or more heatersare moved downhole within the wellboreand installed at desired vertical positions within the wellbore. For example, the heatersmay be installed to the production tubeat heights along a lower zone of the formation, where a substantial amount of the carbonated waterhas collected. Example types of heatersthat may be utilized for the oil recovery operation include mineral insulated downhole heater cables, coiled tubing heater strings, and other types of heaters. In some embodiments, such heaters are controllable via a control skid. In some embodiments, the heatersare low-carbon-intensity heaters.

Although six heatersare illustrated in the example of, in some implementations, anywhere from 1 to 30 heatersmay be installed to the wellboreduring the oil recovery operation. A number and configuration of the heatersmay be selected based one or more of multiple parameters, such as formation thickness, initial formation temperature, targeted formation temperature, a location of a target heating zone, and various hydrocarbon properties, among other parameters.

Still referring to, one or more of the heatersare activated to generate heat within the wellbore. In some examples, the amount of heat generated by the heatersis significantly greater than the amount of heat that could be generated by hot water injection or steam injection in the formation. Therefore, the one or more heatersadvantageously provide a cost-effective manner of delivering heat to the formation.

The heat generated by the heatersspreads from the wellboreand is absorbed by the formation, water, and carbonated water. Such heat absorption gradually causes temperatures of the formation, water, and carbonated waterto increase. In some examples, such temperatures may increase from their respective reference or initial temperatures by tens of degrees to several hundreds of degrees, depending on the number of heaters used and the fluid and rock properties of the formation. Such heat absorption therefore causes CO2 gasto be released from the carbonated water(e.g., as indicated by up arrows), and the CO2 gascontinues to be released as the temperatures increase due to continued activation of the heaters. In some examples, anywhere between about 10% to about 100% of the total CO2 within the carbonated wateris released as CO2 gasduring the heating phase, depending on the temperatures.

illustrates the formationduring an oil recovery phase (e.g., a sweep phase) of the oil recovery operation. Since the released CO2 gasis less dense than the waterand carbonated water, the released CO2 gasrises to an upper zoneof the formationover a period of a few hours to several months, depending on the degree of homogeneousness or heterogeneity, fluid properties, and rock properties of the formation. Within the upper zone, the CO2 gasenergizes the oilwithin the upper zonesuch that a mobility of the oilincreases (e.g., with respect to a reference or initial mobility). In some examples, the mobility of the oilincreases by up to about 40% with respect to a reference or initial mobility due to the presence of the released CO2 gas.

The oilwithin the upper zoneis then recovered from (e.g., produced from, pumped out of, or otherwise removed from) the formationthrough openingsin the production tubingat the wellbore. Owing to the increased mobility of the oil, recovery of the oil is enhanced relative to the level of recovery that would have been achieved without the additional energy provided by the released CO2 gas. For example, advantageously, the total volume of oilrecovered from the formationduring the oil recovery operation illustrated inmay be increased by up to about 40% and may be completed in a period of time that is reduced by up to about 40%. Such oil recovery enhancements are related to a sweep efficiency (e.g. a vertical sweep efficiency), which is the fraction of pore volume (e.g., containing the desired oil) within the formationthat has been invaded or swept by the displacing fluid (e.g., the released CO2 gas).

In some examples, the sweep efficiency resulting from such operation may be advantageously increased by up to about 40% relative to a sweep efficiency (e.g., a reference or initial sweep efficiency) that would have been achieved without the CO2-gas-based increased mobility. The increased sweep efficiency results in a relatively lower-cost oil recovery operation. In some implementations, recovery of the oil(e.g., coinciding with the period of time during which the oilis pumped out of the formation) may be completed over a period of several months to several years.

In some implementations, the sequential water flooding, carbonated water flooding, heating, and oil recovery phases described with respect toeffect a cycle of the oil recovery operation. In some examples, the cycle may be repeated several times during the oil recovery operation. In some examples, the water flooding, carbonated water flooding, and heating phases may be repeated several times before the oil recovery phase is started. In some implementations, a cycle of the oil recovery operation may be carried out by activating one or more heatersduring at least a portion of the carbonated water flooding phase such that heat is delivered to the formationwhile carbonated wateris being provided to the formation. In some examples, the heatersmay be activated simultaneously within a given cycle. In other examples, the heatersmay be activated sequentially or one or more heatersmay be activated alternately within a given cycle. In some implementations, one or more heaters, in addition to being installed within the wellbore, may be installed within the wellboreor one or more other wellbores within the formation. In any of the above-discussed heating patterns and configurations, selective activation of one or more heatersenables control of a diffusion rate of CO2 upward through the formationto the oilin the upper zone.

In some implementations, the above-discussed oil recovery operation can advantageously be performed at any formation that has a relatively low temperature, where conventional oil recovery techniques cannot be carried out. Such example formations include classic formations (e.g., sandstone formations) and non-classic formations (e.g., carbonate formations). In some examples, the oil recovery operation discussed with respect toalso benefits the environment in that injection of the waterand carbonated watercaptures (e.g., sequesters) the CO2 within the earth, thereby reducing greenhouse gas emissions within the atmosphere.

is a flow chart illustrating an example methodof recovering oil from a formation (e.g., the formation). In some embodiments, the methodincludes a stepfor providing carbonated water (e.g., the carbonated waterand/or carbonated water) in a lower zone (e.g., the lower zone) of the formation. In some embodiments, the methodincludes a stepfor releasing carbon dioxide gas from the carbonated water to produce released carbon dioxide gas (e.g., the CO2 gas). In some embodiments, the methodincludes a stepfor causing the released carbon dioxide gas to contact (e.g., invade, infuse, permeate, mix with, interact with, or otherwise contact) oil (e.g., the oil) in an upper zone (e.g., the upper zone) of the formation to increase a mobility of the oil. In some embodiments, the methodincludes a stepfor recovering the oil from the formation.

While the methodhas been described and illustrated with respect to certain sizes, shapes, arrangements, configurations, and formations, in some embodiments, oil may be recovered from a formation using a method that is otherwise substantially similar to the methodbut that may be effected by one or more different sizes, shapes, arrangements, configurations, or formations.

The above-discussed embodiments, implementations, examples and other embodiments, implementations, and examples are within the scope of the following claims.

In an example aspect, a method of recovering oil from a formation includes providing carbonated water in a lower zone of the formation, releasing carbon dioxide gas from the carbonated water to produce released carbon dioxide gas, causing the released carbon dioxide gas to contact oil in an upper zone of the formation to increase a mobility of the oil, and recovering the oil from the formation.

Embodiments may provide one or more of the following features.

In an example aspect combinable with any other example aspect, the method further includes delivering water to the formation.

In an example aspect combinable with any other example aspect, the method further includes mixing the carbonated water with the water in the formation.

In an example aspect combinable with any other example aspect, the method further includes delivering the carbonated water to the formation through lateral openings.

In an example aspect combinable with any other example aspect, the method further includes causing the released carbon dioxide gas to flow from the lower zone of the formation to the upper zone of the formation.

In an example aspect combinable with any other example aspect, increasing a mobility of the oil includes transferring energy from the released carbon dioxide gas to the oil.

In an example aspect combinable with any other example aspect, the method further includes increasing the mobility of the oil by up to about 40%.

In an example aspect combinable with any other example aspect, the method further includes increasing a sweep efficiency of the formation by up to about 40%.

In an example aspect combinable with any other example aspect, the method further includes flowing the carbonated water laterally across the formation.

In an example aspect combinable with any other example aspect, the method further includes installing one or more downhole heaters within the formation.

In an example aspect combinable with any other example aspect, the method further includes activating at least one of the one or more downhole heaters to generate heat within the formation.

In an example aspect combinable with any other example aspect, the method further includes increasing a temperature of the carbonated water from a reference temperature.

In an example aspect combinable with any other example aspect, the carbonated water absorbs the heat to cause the carbon dioxide gas to be released from the carbonated water.

In an example aspect combinable with any other example aspect, the method further includes installing the one or more downhole heaters in one or more wellbores within the formation.

In an example aspect combinable with any other example aspect, the method further includes activating the at least one of the one or more downhole heaters while the carbonated water is being provided in the formation.

In an example aspect combinable with any other example aspect, the one or more heaters comprise low-carbon-intensity heaters.

In an example aspect combinable with any other example aspect, the method further includes a water flooding phase, a carbonated water flooding phase, a heating phase, and a recovery phase.

In an example aspect combinable with any other example aspect, recovering the oil from the formation includes producing the oil from a production tube within the wellbore.

In an example aspect combinable with any other example aspect, the production tube is spaced apart from an injection point for introducing the carbonated water into the formation.

In an example aspect combinable with any other example aspect, the method further includes increasing an amount of oil recovered from the formation with respect to a reference amount that corresponds to a method in which oil is recovered from the formation without utilizing the released carbon dioxide gas.