Method for recovering bitumen from oil sand   

The invention relates generally to a method for recovering oil from oil bearing sand, and more particularly to a recovering of such oil in form of bitumen by a method that includes contacting bitumen-containing sand with a liquid medium.

The world population, especially in the developed and developing industrial countries, consumes enormous amounts of energy. It is estimated that about half of the amount of energy consumed comes from petroleum products. As the traditional sources of oil are being exhausted, and as increased demand supports a relatively high price for oil in the global marketplace, there is a growing need for the development of alternate sources of oil.

One such alternate source of oil is oil bearing sands such as oil shale and tar sands. Despite the fact that enormous amounts of oil are present in the oil shale and tar sand deposits and the fact that such deposits are located in many of the most technologically advanced countries (including the United States and Canada), the amounts of oil actually obtained from these deposits are significantly lower than the amount of oil obtained from traditional oil sources. The reason for this seeming paradox is that oil in the oil shale and tar sands is more difficult and expensive to recover than oil from a traditional oil source.

A number of processes for the recovery of oil from oil sands have been explored over the past few years. These processes include direct combustion (heating or retorting), solvent extraction, water flotation and many variations of these processes to extract oil from the oil sands. Organic material recoverable from oil sands is at times referred to as bitumen. However currently known processes for the extraction of oil in form of bitumen from oil sands face both technical and economic challenges. One important technical disadvantage of known processes is the relatively low recovery rate of bitumen from a treated oil sand. For example, in a water flotation process only about 50 to about 70 percent of the bitumen is recovered from the oil sand. It is difficult to separate and recover bitumen from oil sands because the organic material comprising the oil sand is both a complex chemical mixture and may be bound to the inorganic components of the oil sand and/or physically trapped within the interstices of the sand component of the oil sand. Thus, a variety of bitumen recovery schemes involve the application of heat to the oil sand or solvent treatment of the oil sand in order to enhance the recovery of bitumen from the sand.

One known method of recovering useful organic material from oil sands is referred to as the retorting method, which involves heating the oil sand and recovering a distillate. A serious limitation of the retorting method is that it is energy and capital intensive and produces as a by-product a spent sand which may require further treatment before it can be disposed of appropriately. The energy intensiveness of the process can be better appreciated by considering the cost of sustained heating of large volumes of oil sand at high temperature. Generally temperatures employed in the retorting process range between about 500° C. and about 800° C. Large capital expenditures are needed for equipment used to heat the oil bearing sand, even if the heating is carried out in situ. The oil recovered from oil sands by conventional processes, such as retorting, is not identical in composition to the conventional crude oil recovered from the ground and for many applications such oil sand oil has to be further treated by distillation, coking of residue and/or hydrogenation to achieve the required characteristics.

Another approach to recovering oil from an oil bearing sand has been to extract the oil with one or more solvents. Thus, extractive separation of bitumen from oil sands using organic solvents such as hydrocarbons and is known. In addition, extracting oil from oil shale using a variety of organic solvents at elevated temperatures and at elevated pressures has also been tried. Known extraction processes have not been entirely successful because they employ organic solvents which are generally quite expensive relative to the value of the recovered bitumen and may require the use of high temperatures and high pressures. The use of high temperatures and/or pressures, in turn, necessitates the use of sophisticated and expensive equipment. The solvent employed may itself have a very strong affinity for the sand being treated, and thus recovery of the solvent employed may present an additional technical challenge and economic issue.

There remains a need for the efficient recovery of useful bitumen from oil sand which is responsive to the economic realities of recovering a relatively low-value organic product from an abundant natural resource and the ecological imperative of doing so in a manner consistent with the highest principles of environmental stewardship.

In one aspect, the present invention provides a method for recovering bitumen from an oil sand, the method comprising: (a) contacting a bitumen-containing oil sand with a first solvent mixture of cyclohexane and ethanol to provide an extraction mixture comprising a sand phase and an organic phase; (b) separating the sand phase from the organic phase comprising bitumen, ethanol and cyclohexane; (c) separating an azeotropic mixture comprising cyclohexane and ethanol from the organic phase; and (d) recovering bitumen from the organic phase. The first solvent mixture comprises from about 95 to about 65 percent cyclohexane and from about 5 to about 35 percent ethanol.

In another aspect, the present invention provides a method for recovering bitumen from an oil sand, the method comprising: (a) contacting in situ a bitumen-containing oil sand in a subsurface deposit with a first solvent mixture of cyclohexane and ethanol to provide an extraction mixture comprising a sand phase and an organic phase; (b) removing the organic phase comprising bitumen, cyclohexane and ethanol from the subsurface deposit; (c) separating an azeotropic mixture comprising cyclohexane and ethanol from the organic phase; and (d) recovering bitumen from the organic phase. The first solvent mixture comprising from about 95 to about 65 percent cyclohexane and from about 5 to about 35 percent ethanol.

In yet another aspect, the present invention provides a method for recovering bitumen from an oil sand, the method comprising: (a) contacting at ambient temperature a bitumen-containing oil sand with a first solvent mixture comprising about 69 cyclohexane and about 31 percent ethanol to provide an extraction mixture comprising a sand phase and an organic phase; (b) separating the sand phase from the organic phase comprising bitumen, ethanol and cyclohexane; (c) separating an azeotropic mixture comprising cyclohexane and ethanol from the organic phase; and (d) recovering bitumen from the organic phase. The first solvent mixture being used in an amount corresponding to a weight ratio of first solvent mixture to oil sand in a range from about 3 to 1 to about 500 to 1.

DETAILED DESCRIPTION

In the following specification and the claims, which follow, reference will be made to a number of terms, which shall be defined to have the following meanings.

The singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.

It is also understood that terms such as “top,” “bottom,” “outward,” “inward,” and the like are words of convenience and are not to be construed as limiting terms. Furthermore, whenever a particular feature of the invention is said to comprise or consist of at least one of a number of elements of a group and combinations thereof, it is understood that the feature may comprise or consist of any of the elements of the group, either individually or in combination with any of the other elements of that group.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Similarly, “free” may be used in combination with a term, and may include an insubstantial number, or trace amounts, while still being considered free of the modified term.

As discussed in detail below, embodiments of the present invention include a method for recovering bitumen from an oil sand, the method comprising: (a) contacting a bitumen-containing oil sand with a first solvent mixture of cyclohexane and ethanol to provide an extraction mixture comprising a sand phase and an organic phase; (b) separating the sand phase from the organic phase comprising bitumen, ethanol and cyclohexane; (c) separating an azeotropic mixture comprising cyclohexane and ethanol from the organic phase; and (d) recovering bitumen from the organic phase.

As used herein “oil sands” also includes but not limited to tar sands, extra heavy oils, oily sludge wastes, oil-bearing diatomites, oil shales, tar saturated sandstones and the like. Further, oil sands as used herein also include mined oil sands as well as crude output from steam assisted gravity drainage processes (SAG-D processes). The methods provided by the present invention may be applied to both mined oil sands (oil sands removed from a first location to a second location for treatment), and subsurface oil sand deposits. When applied to a subsurface oil sand deposit the method is at times herein referred to as an in-situ recovery method, and for example, the oil sand is said to be contacted in situ with the first solvent mixture to provide an extraction mixture.

Oil sands are a type of bitumen deposit which may be found as deposits near the surface of the earth or in subsurface deposits. Oil sand deposits located near the surface of the earth may be mined using surface mining techniques and transported from a first location where the oil sand is mined to a second location where the oil sand is subjected to treatment for bitumen recovery. In one embodiment, the oil sand is a subsurface deposit not readily accessible using surface mining techniques.

The oil sands may comprise a mixture of sand, clay, water, organometallic compounds, and a dense and viscous form of petroleum also known as bitumen. Oil sands may also be referred to as “unconventional oil” or “crude bitumen”. Bitumen is especially prone to the formation of highly stable emulsions due to its chemical complexity which varies from deposit to deposit, its occurrence in nature with water containing a variety of inorganic species, and the considerable shear forces that the contents of an oil deposit may experience during capture by a man-made conduit.

As noted, the present invention provides a method in which a bitumen-containing oil sand is contacted with a first solvent mixture. The first solvent mixture includes a mixture of cyclohexane and ethanol. In one embodiment, the first solvent mixture includes cyclohexane and ethanol in a ratio from about 95 weight percent to about 65 weight percent of cyclohexane and from about 5 weight percent to about 35 weight percent of ethanol based on the total weight of the first solvent mixture. In another embodiment, the first solvent mixture includes a mixture of cyclohexane and ethanol in a ratio from about 90 weight percent to about 65 weight percent of cyclohexane and from about 10 weight percent to about 35 weight percent of ethanol based on the total weight of the first solvent mixture. In yet another embodiment, the first solvent includes a mixture of cyclohexane and ethanol in a ratio from about 70 weight percent cyclohexane and about 30 weight percent of ethanol based on the total weight of the first solvent mixture. In a particular embodiment, the first solvent mixture comprises cyclohexane and ethanol in a ratio from about 69 weight percent cyclohexane and about 31 weight percent ethanol based on the total weight of the first solvent mixture.

In one embodiment, the first solvent is used in an amount corresponding to a weight ratio of first solvent mixture to the oil sand in a range from about 3 to 1 to about 500 to 1. In another embodiment, the first solvent is used in an amount corresponding to a weight ratio of first solvent mixture to oil sand in a range from about 3 to 1 to about 50 to 1. In yet another embodiment, the first solvent is used in an amount corresponding to a weight ratio of first solvent mixture to oil sand in a range from about 3 to 1 to about 10 to 1.

In one embodiment, the contacting of the bitumen-containing oil sand with the first solvent mixture is carried out for a period of time ranging from about 0.1 hour to about 24 hours. In another embodiment, the contacting of the bitumen-containing oil sand with the first solvent mixture is carried out for a period of time ranging from about 3 hour to about 15 hours. In one embodiment, the contacting of the bitumen-containing oil sand and the first solvent mixture is carried out at a temperature a range from about 25° C. to about 150° C. In another embodiment, the contacting of the bitumen-containing oil sand and the first solvent mixture is carried out at a temperature a range from about 45° C. to about 120° C. In yet another embodiment, the contacting is carried out at ambient temperature. In one embodiment, steam may be contacted with the extraction mixture.

The contacting of the bitumen-containing oil sand with the first solvent provides an extraction mixture. The extraction mixture includes a sand phase and an organic phase. The organic phase includes bitumen, ethanol and cyclohexane. The sand phase is separated from the organic phase. The separation of the sand phase from the organic phase may be carried out by techniques known to one skilled in the art. In one embodiment, the separation of the sand phase and the oil phase may be carried out by gravity separation, i.e. a separation in which the product is subjected to defined gravitational forces tending to separate the heavier sand from the lighter fluids. Examples of gravitational separation include but are not limited to centrifugation, separation using a hydrocyclone, rotary filtration, simple filtration, and the like. In one embodiment, a hydrocyclone separation is employed which includes a plurality of separating stages. In certain embodiments, the sand phase obtained following contact with the first solvent mixture may be discarded as bitumen-free and solvent-free sand. In certain other embodiments, the sand phase may be separated from the extraction mixture and thereafter be subjected to a second stage of extraction. In embodiments in which the oil sand is being treated in situ, the organic phase is removed from the spent sand phase by bringing the organic phase to the surface. In embodiments involving in situ contacting of an oil sand with the first solvent mixture in a subsurface deposit, the first solvent mixture is introduced into the subsurface deposit via at least one solvent inlet conduit. The organic phase resulting from the contacting of the oil sand with the first solvent mixture is thereafter removed via one or more outlet conduits. In one embodiment, the solvent inlet conduit also serves as the outlet conduit. In one embodiment, the solvent inlet conduit delivers the first solvent to a subsurface oil sand deposit while a plurality of outlet conduits arrayed radially about the edge of the subsurface oil sand deposit removes the resultant organic phase comprising bitumen, cyclohexane and ethanol. In order to enhance the recovery of bitumen and solvent from the subsurface oil sand deposit, the first solvent mixture may be heated prior to or during contact with the subsurface oil sand. In one embodiment, an inert gas or steam is used to enhance the removal of the organic phase from the subsurface oil sand deposit. In one embodiment, carbon dioxide is used to enhance the removal of the organic phase from the subsurface oil sand deposit.

The organic phase separated from the sand phase may be treated in order to separate and recover the cyclohexane and ethanol employed and to recover the bitumen component of the organic phase. In one embodiment, the organic phase is subjected to conditions under which the cyclohexane and ethanol is removed from the organic phase by distillation. In various embodiments cyclohexane and ethanol are recovered as an azeotropic mixture comprising about 69% cyclohexane and about 31% ethanol. As is demonstrated herein, the use of an azeotropic mixture of cyclohexane and ethanol provides a two-fold advantage in that the azeotropic mixture has a significantly lower boiling point (64.9° C.) than either of its constituents solvents cyclohexane (80.7° C.) and ethanol (78° C.); and the extraction efficiency of cyclohexane-ethanol mixture with respect to bitumen recovery is superior to the pure solvents. The lower boiling point of the azeotropic mixture allows recovery of the first solvent mixture for reuse at a lower cost since less energy is required to effect its distillation. Thus, in one embodiment, an azeotropic mixture of cyclohexane and ethanol is separated from the organic phase. Those of ordinary skill in the art will understand that a cyclohexane-ethanol mixture comprising 69% cyclohexane and 31% ethanol will have essentially the same composition before and after distillation. When an azeotropic mixture (also sometimes referred to as constant boiling mixture) is boiled the resulting vapor has the same ratio of the constituents cyclohexane and ethanol, as the original mixture. The separating of the azeotropic mixture from the organic phase may be carried out by several methods known to one skilled in the art for example distillation, pressure swing distillation, extractive distillation, chemical action separation, pervaporation, vapor permeation and the like. In one embodiment, the separating the azeotropic mixture is carried out by distillation. In one embodiment, the distillation is carried out at a pressure in a range from about 0.1 atmospheres to about 5 atmospheres. In another embodiment, the separating the azeotropic mixture is carried out by distillation at ambient pressure.

Recovery of bitumen from the organic phase may be carried out by techniques known to one skilled in the art such as centrifugation, filtration and the like. In one embodiment, recovering of the bitumen from the organic phase includes reducing the temperature of the organic phase to effect precipitation of the bitumen from the organic phase and thereafter centrifuging of the mixture to further separate the bitumen from the organic phase. In one embodiment, the centrifugation of the organic phase is carried out at a temperature in a range from about minus 40° C. to about 25° C. In another embodiment, the centrifugation of the organic phase is carried out at a temperature in a range from about minus 5° C. to about 20° C. In one embodiment, centrifugation results in the formation of a lower bitumen layer and a supernatant liquid comprised chiefly of the first solvent mixture. The supernatant liquid may be decanted from the lower bitumen layer following centrifugation. In one embodiment, the recovery of the bitumen from the organic phase is carried out prior to separating the azeotropic mixture from the organic phase. In another embodiment, the recovery of bitumen from the organic phase is carried out following separating the azeotropic mixture from the organic phase. In one embodiment, the extraction mixture is distilled to provide an “overhead” stream comprising an azeotropic mixture of cyclohexane and ethanol and a “bottoms” stream of bitumen fluid. Such a process is amenable to continuous process steps operated at steady state.

In one embodiment of the present invention, the method further includes a drying step in which the organic phase is treated with a drying agent prior to separation of the azeotropic mixture comprising cyclohexane and ethanol. Non-limiting examples of drying agents include anhydrous salts such as calcium chloride (CaCl2), sodium sulfate (Na2SO4), calcium sulfate, magnesium sulfate (MgSO4), and the like. In one embodiment, the sand phase after separation from the organic phase (spent sand) may be heated to remove any residual water and may be employed as a drying agent in the drying step.

In some embodiments, the method includes a step of transporting the organic phase to a second location remote from a first location at which the contacting is carried out. In one embodiment, the transporting comprises transport by pipeline.

In various embodiments, the bitumen recovered may be transported and eventually upgraded into higher value products, for example synthetic oil. In one embodiment, the bitumen obtained after the recovery step includes less than about 1 parts per million (ppm) of impurities such as vanadium, nickel and sulfur compounds. In another embodiment, less than about 1 ppm of impurities such as vanadium compounds.

In another aspect of the present invention a method for recovering bitumen from an oil sand that includes (a) contacting in-situ a bitumen-containing oil sand in a subsurface deposit with a first solvent mixture of cyclohexane and ethanol to provide an extraction mixture, a sand phase and an organic phase, the first solvent mixture comprising from about 95 to about 65 percent cyclohexane and from about 5 to about 35 percent ethanol; (b) removing the organic phase comprising bitumen, cyclohexane and ethanol from the subsurface deposit; (c) separating an azeotropic mixture comprising cyclohexane and ethanol from the organic phase; and (d) recovering bitumen from the organic phase. In one embodiment, the order of the steps may be interchangeable. In another embodiment, the order of steps (a)-(d) is first (a) then (b) then (c) then (d).

In another embodiment, the methods includes (a) contacting at ambient temperature a bitumen-containing oil sand with a first solvent mixture comprising about 69 cyclohexane and about 31 percent ethanol to provide an extraction mixture comprising a sand phase and an organic phase; the first solvent mixture being used in an amount corresponding to a weight ratio of first solvent mixture to oil sand in a range from about 3 to 1 to about 500 to 1; (b) separating the sand phase from the organic phase comprising bitumen, ethanol and cyclohexane; (c) separating an azeotropic mixture comprising cyclohexane and ethanol from the organic phase; and (d) recovering bitumen from the organic phase.

Oil sand models were prepared as follows. Britesorb® D350EL silica adsorbent (approximately 35 grams) was added to a blender, together with approximately 100 g of Saudi heavy crude oil and 200 g of petroleum ether. The resulting slurry was mixed for about five minutes at room temperature and was then poured into centrifuge tubes. Each tube was centrifuged, and the resulting liquid fractions were decanted from the Britesorb® D350EL solids containing crude oil. The solids were dried under vacuum at 80° C. for about two hours. The dried solids were then analyzed using a Thermogravimetric Analyzer (TGA). The percent weight loss between the initial onset of devolatization and/or decomposition at about 200° C. to about 650° C. was interpreted to reflect the removal of the residual organic material (oil components) from the adsorbent. The results indicated that the model oil sands comprised about 34.2 wt. % oil components.

First solvent mixtures (wash solutions) comprising cyclohexane and ethanol were prepared and are given in Table 1 together with data for the recovery of oil components.

Oil sand models were contacted with first solvent mixture as follows. The oil sand model (0.5 g) was placed in a vial along with about 13 g of the particular wash solution being tested. The resulting slurry was mixed for about five minutes on an auto-shaker at room temperature and poured into a centrifuge tube. The tube was centrifuged and the resulting organic phase was decanted away from the model sand phase. The model sand phase was contacted two additional times with the same solvent mixture as before. The model sand thus recovered was analyzed by thermogravimetric analysis (TGA) to determine an amount of oil remaining on the solid phase.

TGA was performed on 5-10 mg samples. The temperature was increased at a rate of 10-20° C./minute to the desired final temperature in a range from about 650° C. to about 700° C. During the analysis the sample was exposed to a constant flow of air at 0.04 standard cubic feet per hour. As the temperature increased, oil components were volatilized and/or decomposed and thereby removed from the solid adsorbent resulting in a corresponding weight loss. The weight loss corresponds precisely to the oil that was present within the adsorbent. By knowing the amount of oil initial present in the model oil sand and the amount of oil remaining after washing, an efficacy of the wash step can be quantified. Exemplary results are set forth in Table 1 below. The data show the unique ability of solvent mixtures having compositions comprising from about 95 to about 65 percent cyclohexane and from about 5 to about 35 percent ethanol to effect the removal of the oil components from the oil sand model.

TABLE 1 Cyclohexane Ethanol Oil Removed Vanadium TGA (wt %) (wt %) (%) (ppm) % wt loss CEx. 1 100 0 41.4 — — CEx. 2 10 90 36.9 0.6 5.31 CEx. 3 0 100 35.4 <0.1   32.76  Ex. 1 90 10 99.3 — — Ex. 2 75 25 98.0 — — Ex. 3 50 50 71.8 — — Ex. 4 25 75 46.8 0.5 5.87

The foregoing examples are merely illustrative, serving to exemplify only some of the features of the invention. The appended claims are intended to claim the invention as broadly as it has been conceived and the examples herein presented are illustrative of selected embodiments from a manifold of all possible embodiments. Accordingly, it is the Applicants\' intention that the appended claims are not to be limited by the choice of examples utilized to illustrate features of the present invention. As used in the claims, the word “comprises” and its grammatical variants logically also subtend and include phrases of varying and differing extent such as for example, but not limited thereto, “consisting essentially of” and “consisting of.” Where necessary, ranges have been supplied; those ranges are inclusive of all sub-ranges there between. It is to be expected that variations in these ranges will suggest themselves to a practitioner having ordinary skill in the art and where not already dedicated to the public, those variations should where possible be construed to be covered by the appended claims. It is also anticipated that advances in science and technology will make equivalents and substitutions possible that are not now contemplated by reason of the imprecision of language and these variations should also be construed where possible to be covered by the appended claims.