US3040809A - Process for recovering viscous crude oil from unconsolidated formations - Google Patents

Description

Unite This invention relates to a process for the recovery of mineral oil from subterranean formations. More particularly, the present invention is concerned with a process for the recovery of oil by thermal recovery means involving the use of a hot, upwardly how of inert gas in subterranean oil-bearing formations characterized by unconsolidated sands or friable structures such as is indigenous to the region surrounding the Athabasca river in northern Alberta, Canada, and the western region of the United States. These unconsolidated or friable structures are porous and are either of a fluent nature, i.e. they crumble under the weight of the overburden or they are held together by hydrocarbons such that if the hydrocarbons are extracted as with toluene, the sands collapse. The sands are readily distinguishable from oil shale which is consolidated and non-porous.

In the region surrounding the Athabasca river in Alberta, Canada, large deposits of tar sands exist. The significance of these deposits as a potential source of oil is apparent since they contain, it has been estimated, about 200 billion barrels of oil. The oil present in Althab asca tar sand frequently has a gravity of between about 5 and 15 API and is present to an extent of about to 20 weight percent. The recovery problem, however, presents a number of difliculties, both from a technical and an economic standpoint. Proposals have been made to mine the sands and recover oil from the mined sand by various operations requiring mechanical preparation followed by washing or heating methods. The cost of these operations, were they to be performed on a large scale, would be excessive both in terms of capital investment and operating expenses. In the western region of the United States there also exist unconsolidated subterranean sands bearing heavy mineral oils whose recovery presents problems similar to those faced in the Athabasca region except for climate and transportation considerations.

Various methods have been devised for the recovery of oil and gas from subterranean formations, which, at this time, may be termed conventional. These methods are to 'a great extent, supplementary to each other and can be presented in the order in which they are applied to a given formation. In the first instance, upon the establishment of communication from the surface of the earth to a subterranean oil and gas bearing formation, the oil and gas are frequently forced through the communication means to the surface under the pressure prevailing in the formation. Following the exhaustion of a significant amount of pressure in the formation such that the natural flow of oil up the well bore "ceases, recovery of the oil is continued by pumping means. However, when a negligible amount of oil flows freely to the Well for pumping, the formation is sometimes repressured to drive the oil from the formation to the well. When repr'essu'ring is inexpedient, the oil can be forced into the well from an adjacent formation by driving a liquid, e.g. water, or gaseous medium through the formation as from an input to an output well. The processes employed to recover oil, after pumping becomes disadvantageous, are sometimes referred to as secondary recovery methods.

In more recent times, thermal recovery methods have become of interest for application to the oil-bearing foratent mations to enhance oil recovery. Such thermal means have often been proposed to effect more efficient oil recovery whereby the thermal energy is introduced into the formation by means of hot liquids or gases.

The present invention is advantageous since conventional methods for the recovery of oil from subterranean formations are inadequate when dealing with oil-bearing strata comprising unconsolidated sands or friable structures of the character found in the Athabasca and western United States region, which contain heavy oil of less than about 20 API gravity, e.g. about 5 to 15. The invention relates to a process which employs thermal means to recover oil from such formations having uninterrupted vertical permeability, that is, the formation is essentially devoid of impermeable structures such as shale, clay and the like positioned to block upward flow of gas. This vertical permeability extends through the oil bearing sand for at least about 50 feet and preferably at least about feet for economical operation. In using the term vertical I refer to a generally upward direction.

In my process, hot inert gas is introduced into a lower portion of the unconsolidated formation and conducted upwardly through the formation, eg for at least about 50 or 100 feet. The gas is then withdrawn from the formation by any suitable means providing an area of reduced pressure to insure the upward direction of gas flow. Thus, the oil-bearing formation is progressively heated from a lower to an upper region and as this is accomplished the heavy oil flows downwardly through the formation, countercurrent to the flow of gas, to a point or collection area where it can be recovered by suitable means, for example, by pumping or by a gas lift. Conveniently, the oil collection point is at or below the posit-ion of upfiowing gas introduction. After the formation has been heated to about 500 [to about 800 F., preferably about 600 to about 750 F., for a vertical distance of at least about 50 or 100 feet, the upward flow of inert gas may be discontinued, and a downward flow of inert gas applied to the formation to drive the oil to the recovery point or collection area. The introduction point of the gas in the latter operation is usually spaced vertically at least about 50 feet, preferably at least about 100' feet, above the point of introduction of the upflowing gas. Conveniently, the downfiowing gas is introduced into the formation at the position of withdrawal of the upflowing gas, and the downflowing gas is withdrawn from the formation where the upflowing gas is introduced.

The gases used in my process are inert to combustion and will include CO fuel gas, CH N etc. and no or only small amounts of O insufficient to cause any significant combustion of hydrocarbons present. The gas may contain free hydrogen which could serve to increase the hydrogen to carbon ratio in the oil and decrease its viscosity. Although I prefer substantially no free 0 in these gases, the permissible amount of 0 which can be tolerated is variable and depends primarily upon the temperature and the character of the introduced gas and the hydrocarbons and carbon deposits in the formation. The temperature of the gas likewise depends upon the char acter of the formation and the temperature desired therein; however, temperatures for the upflowing gas in the range of about 500 F. to about 800 F. are usable although temperatures in the range of about 600 F. to 750 F. are preferred and about 700 F seems optimum. The downflowing gas can be introduced into the formation at any temperature of up to about 800 F. Preferably, this gas is at ambient temperature or at the temperature at which it is available to the working site. The downflowing gas is inert as described above and the gas might be produced in-situ through heating of an injected liquid such as Water or light hydrocarbons.

The superficial velocity of the gas passing upwardly through the formation is also dependent upon the nature of the formation. Since the residual oil in the formation flows counter to the gas flow, the velocity of the gas is limited to a maximum which will not adversely affect the flow of oil, e.g. a maximum of about 60 feet per minute. The minimum velocity is determined by heat requirements in the heating of the formation as well as economical considerations, and is usually at least about 0.1 foot per hour; however, a superficial velocity in the range of about 1 foot to about feet per minute is preferred. The velocity of the downflowing gas can be as desired but, of course, the pressure of introduction must be sufiicient to maintain gas flow. The upward and downward flows of gas are conducted through a section of the formation extending, from the point the gas is introduced into the formation, vertically to about 30 from the horizontal to the point of introduction, preferably from vertically to about 60 from the horizontal. The gas used in my method can be heated either on the surface or by a heating unit or burner in the well.

The advantage in using any upflowirrg, heated gas was shown in a small scale experiment. Thus, a sand pack, representative of the Athabasca tar sands, having.

an initial permeability when cold of 110 ft. /hr. of gas at 27.5 psi. was subjected to downflowing hot inert gases, and the flow of gas ceased at 90 p.s.i. in less than one hour. It is believed that the cause of blockage was due to the flow of hot oil, of a viscous character, into cold sand where it became solid or immobile, thus plugging all available gas pore space.

The feasibility of my method has been confirmed in a test using a 1072 gram quantity of simulated Athabasca tar sand containing 14.9 percent by weight of 10 API gravity, 500 SUS viscosity at 210 F. residual South Texas crude bottoms and 85.1 percent by weight of builders sand, a 100 gram sample of which was analyzed using a screen test, with the following results:

Retained on screen: Quantity, grams A 2 steel tube (3.35 square inches in cross-section) in length, packed with 1072 grams of the abovedescribed simulated Athabasca tar sand, and having a A" nippled opening at each of its two ends, with the lower nipple containing a bubble cap to prevent sand clogging while gas is passed freely therethrough and into the sand pack, is vertically and centrally disposed in a cylindrical container. extends downwardly with the nipple protruding through a close-fitting opening in the bottom of the tank. Another line used, for the recovery of oil accumulating in the bottom of the tube, provides communication means downwardly from the bottom of the tube, through the bottom of the tank and into an oil receiving container. Three sets of electrical heating coils are placed around the tubing and are vertically spaced up the tubing. The container holding the tube contains insulation to minimize heat losses. The depth of the sand pack in the tube is 12".

The process of my invention is confirmed using the above material and equipment in the following manner. During a 3-hour period, 24.22 cubic feet of cool engine exhaust gas, at an average rate of flow of 0.16 cubic foot/min, and an average superficial velocity of 6.85 feet/min. are conducted upwardly, through the capped nipple of the tube, the packed sand, and is vented through the top nipple. The heating coils serve to heat the gas The end with the capped nipple and sand pack and the average temperature of the bottom section of the sand is 437 F. The middle section of the sand has an average temperature of 500 F., while the top section has an average temperature of 450 F. Seventeen grams of oil, essentially of the same gravity as that initially mixed with the said are recovered. After the 3-hour period, using the same sand pack, and during a 65-hour period; 12.58 cubic feet of engine exhaust gas, at an average rate of flow of 0.032 cubic foot/min. and an average superficial velocity of 1.37 feet/min. are conducted, in the same manner as the previous volume of gas, upwardly through the capped nipple, the packed sand, and is vented at the top nipple. The average temperatures of the sand are: bottom section, 603 F.; middle section, 663' F.; and top section, 703 F. Fortyone grams of oil, essentially of the same gravity as the initial charge, are recovered through the oil recovery line.

Following the above sweep of gas upwardly through the tube, the gas flow is reversed and the sand pack is swept with a downward flow of gas during a 8.16-hour period. 49.46 cubic feet/min. of engine exhaust gas, at an average rate of flow of 0.1 cubic foot/min, and an average superficial velocity of 4.30 feet/min. are conducted downwardly through the top nipple of the tube, the sand pack, and passed, along with the oil, through the oil recovery line. The average temperatures of the sand pack are: top section, 703 F.; middle section, 663 F.; and bottom section, 603 F. Eighteen additional grams of oil, essentially of the same gravity as that initially mixed, are recovered through the oil recovery line. Thus, 47 .5- weight percent of the initially mixed oil is recovered by this procedure.

Field use of my method as applied to Athabasca or similar sands will most advantageously be employed on formations of the greatest thickness at the least available depth. Well patterns or other access to the formation can be developed along several lines. For instance, vertical wells can be drilled to the position of introduction of the upflowing gas, and the gas may exit in the upper portion of the same well or in a spaced or adjacent output Well. Then the downfiowiug gas, if used, can be applied in the reverse path, and oil is recovered from the well location of initial gas input. Access out into the formation from vertical Wells can be effected by horizontal drilling at the desired point. Also, horizontal access can be made from a natural outcrop of the sand.

In a typical example of my process, a well is drilled from the earths surface to the bottom of a formation of Athabasca tar sand 200 feet in thickness, and then horizontally away from the vertical bore for fifty feet. The well is cased and a liner is inserted in the horizontal hole. A second well, located 50 feet from the first and near the ends of the horizontal hole of the first Well, is drilled from the earths surface to the top of the tar sand formation and then horizontally for 50 feet towards the first well. The second well is cased and lined similar to the first well. An internal combustion heating unit is inserted into the first well and it heats flue gas passing downwardly into the well to a temperature of 700 F. The heated flue gas, at a superficial space velocity of 9 feet/min, is conducted through the liner, and upwardly through the formation, which is progressively heated thereby, to the second well or the gas takeoff well where the gas is recovered and recycled. Residual oil in the formation, flows downwardly to the bottom of the first well where it is pumped out and recovered. After the formation is heated to a temperature of 700 F., the flow of gas at the same velocity is reversed, i.e. into the second well, downwardly to the bottom of and out of the first well; thus sweeping additional amounts of oil to the bottom of the first well from which it is recovered. No

a heater is used in the second well during reverse gas flow.

I claim: 1. A method for the recovery of heavy oil from a 5 formation of unconsolidated sands having vertical permeability, said oil having an API gravity of less than about 20, the steps comprising introducing hot inert gas at a temperature from about 500 to 800 F, into a lower portion of the unconsolidated formation via a well therein, conducting the gas upwardly through the formation at a superficial velocity of about 1 foot to 10 feet per minute to progressively heat the formation from a lower to an upper region at a rate sufiicient to allow the heavy oil to flow downwardly through the formation to an area of collection adjacent the lower portion of the formation, and continuing to conduct the hot inert gas upwardly through the formation to maintain the progressive heating by contacting the formation from a lower to an upper region by taking oil gas in the upper portion of the formation 15 2,857,002

References Cited in the file of this patent UNITED STATES PATENTS 1,816,260 Lee July 28, 1931 2,421,528 Stelfen 'June 3, 1947 2,813,583 Marx et al Nov. 19, 1957 2,819,761 Popham et a1. Jan. 14, 1958 Pevere et al Oct. 21, 1958