Patent Publication Number: US-2012037363-A1

Title: Systems and methods for producing oil and/or gas

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to systems and methods for producing oil and/or gas. 
     BACKGROUND OF THE INVENTION 
     Enhanced Oil Recovery (EOR) may be used to increase oil recovery in fields worldwide. There are three main types of EOR, thermal, chemical/polymer and gas injection, which may be used to increase oil recovery from a reservoir, beyond what can be achieved by conventional means—possibly extending the life of a field and boosting the oil recovery factor. 
     Thermal enhanced recovery works by adding heat to the reservoir. The most widely practiced form is a steam drive, which reduces oil viscosity so that it can flow to the producing wells. Chemical flooding increases recovery by reducing the capillary forces that trap residual oil. Polymer flooding improves the sweep efficiency of injected water. Miscible injection works in a similar way to chemical flooding. By injecting a fluid that is miscible with the oil, trapped residual oil can be recovered. 
     Referring to  FIG. 1 , there is illustrated prior art system  100 . System  100  includes underground formation  102 , underground formation  104 , underground formation  106 , and underground formation  108 . Production facility  110  is provided at the surface. Well  112  traverses formations  102  and  104 , and terminates in formation  106 . The portion of formation  106  is shown at  114 . Oil and gas are produced from formation  106  through well  112 , to production facility  110 . Gas and liquid are separated from each other, gas is stored in gas storage  116  and liquid is stored in liquid storage  118 . 
     U.S. Pat. No. 5,826,656 discloses a method for recovering waterflood residual oil from a waterflooded oil-bearing subterranean formation penetrated from an earth surface by at least one well by injecting an oil miscible solvent into a waterflood residual oil-bearing lower portion of the oil-bearing subterranean formation through a well completed for injection of the oil miscible solvent into the lower portion of the oil-bearing formation; continuing the injection of the oil miscible solvent into the lower portion of the oil-bearing formation for a period of time equal to at least one week; recompleting the well for production of quantities of the oil miscible solvent and quantities of waterflood residual oil from an upper portion of the oil-bearing formation; and producing quantities of the oil miscible solvent and waterflood residual oil from the upper portion of the oil-bearing formation. The formation may have previously been both waterflooded and oil miscible solvent flooded. The solvent may be injected through a horizontal well and solvent and oil may be recovered through a plurality of wells completed to produce oil and solvent from the upper portion of the oil-bearing formation. U.S. Pat. No. 5,826,656 is herein incorporated by reference in its entirety. 
     Co-pending U.S. Patent Application Publication Number 2006/0254769, published Nov. 16, 2006, and having attorney docket number TH2616, discloses a system including a mechanism for recovering oil and/or gas from an underground formation, the oil and/or gas comprising one or more hydrocarbons; a mechanism for converting at least a portion of the hydrocarbons from the recovered oil and/or gas into a carbon disulfide formulation; and a mechanism for releasing at least a portion of the carbon disulfide formulation into a formation. U.S. Patent Application Publication Number 2006/0254769 is herein incorporated by reference in its entirety. 
     There is a need in the art for improved systems and methods for enhanced oil recovery. There is a further need in the art for improved systems and methods for enhanced oil recovery using a solvent, for example through viscosity reduction, chemical effects, and miscible flooding. There is a further need in the art for improved systems and methods for solvent miscible flooding. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention provides a system for producing oil and/or gas from an underground formation including a well above the formation; a mechanism to inject an enhanced oil recovery formulation into the formation, the enhanced oil recovery formulation including dimethyl ether; and a mechanism to produce oil and/or gas from the formation. 
     In another aspect, the invention provides a method for producing oil and/or gas including injecting a dimethyl ether formulation into a formation from a first well; and producing oil and/or gas from the formation from a second well. 
     Advantages of the invention include one or more of the following: 
     Improved systems and methods for enhanced recovery of hydrocarbons from a formation with a solvent. 
     Improved systems and methods for enhanced recovery of hydrocarbons from a formation with a fluid containing a miscible solvent. 
     Improved compositions and/or techniques for secondary recovery of hydrocarbons. 
     Improved systems and methods for enhanced oil recovery. 
     Improved systems and methods for enhanced oil recovery using a miscible solvent. 
     Improved systems and methods for enhanced oil recovery using a compound which is miscible with oil in place. 
     Improved systems and methods for handling produced gas. 
     Improved systems and methods for reducing or eliminating flaring or reinjection of produced gas. 
     Improved systems and methods for converting gases to liquids. 
     Improved systems and methods for recovering and transporting oil and gas from a formation. 
     Improved systems and methods for maintaining formation pressure. 
     Improved systems and methods for maintaining production rates. 
     Improved systems and methods for increasing the life of a reservoir. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an oil and/or gas production system. 
         FIG. 2   a  illustrates a well pattern. 
         FIGS. 2   b  and  2   c  illustrate the well pattern of  FIG. 2   a  during enhanced oil recovery processes. 
         FIGS. 3   a - 3   c  illustrate oil and/or gas production systems. 
         FIG. 4  illustrates an oil and/or gas production method. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Well Spacing 
     Referring now to  FIG. 2   a , in some embodiments, an array of wells  200  is illustrated. Array  200  includes well group  202  (denoted by horizontal lines) and well group  204  (denoted by diagonal lines). 
     Each well in well group  202  has horizontal distance  230  from the adjacent well in well group  202 . Each well in well group  202  has vertical distance  232  from the adjacent well in well group  202 . 
     Each well in well group  204  has horizontal distance  236  from the adjacent well in well group  204 . Each well in well group  204  has vertical distance  238  from the adjacent well in well group  204 . 
     Each well in well group  202  is distance  234  from the adjacent wells in well group  204 . Each well in well group  204  is distance  234  from the adjacent wells in well group  202 . 
     In some embodiments, each well in well group  202  is surrounded by four wells in well group  204 . In some embodiments, each well in well group  204  is surrounded by four wells in well group  202 . 
     In some embodiments, horizontal distance  230  is from about 5 to about 1000 meters, or from about 10 to about 500 meters, or from about 20 to about 250 meters, or from about 30 to about 200 meters, or from about 50 to about 150 meters, or from about 90 to about 120 meters, or about 100 meters. 
     In some embodiments, vertical distance  232  is from about 5 to about 1000 meters, or from about 10 to about 500 meters, or from about 20 to about 250 meters, or from about 30 to about 200 meters, or from about 50 to about 150 meters, or from about 90 to about 120 meters, or about 100 meters. 
     In some embodiments, horizontal distance  236  is from about 5 to about 1000 meters, or from about 10 to about 500 meters, or from about 20 to about 250 meters, or from about 30 to about 200 meters, or from about 50 to about 150 meters, or from about 90 to about 120 meters, or about 100 meters. 
     In some embodiments, vertical distance  238  is from about 5 to about 1000 meters, or from about 10 to about 500 meters, or from about 20 to about 250 meters, or from about 30 to about 200 meters, or from about 50 to about 150 meters, or from about 90 to about 120 meters, or about 100 meters. 
     In some embodiments, distance  234  is from about 5 to about 1000 meters, or from about 10 to about 500 meters, or from about 20 to about 250 meters, or from about 30 to about 200 meters, or from about 50 to about 150 meters, or from about 90 to about 120 meters, or about 100 meters. 
     In some embodiments, array of wells  200  may have from about 10 to about 1000 wells, for example from about 5 to about 500 wells in well group  202 , and from about 5 to about 500 wells in well group  204 . 
     In some embodiments, array of wells  200  is seen as a top view with well group  202  and well group  204  being vertical wells spaced on a piece of land. In some embodiments, array of wells  200  is seen as a cross-sectional side view with well group  202  and well group  204  being horizontal wells spaced within a formation. 
     Referring now to  FIG. 2   b , in some embodiments, array of wells  200  is illustrated. Array  200  includes well group  202  (denoted by horizontal lines) and well group  204  (denoted by diagonal lines). 
     In some embodiments, a miscible enhanced oil recovery agent is injected into well group  204 , and oil is recovered from well group  202 . As illustrated, the miscible enhanced oil recovery agent has injection profile  208 , and oil recovery profile  206  is being produced to well group  202 . 
     In some embodiments, a miscible enhanced oil recovery agent is injected into well group  202 , and oil is recovered from well group  204 . As illustrated, the miscible enhanced oil recovery agent has injection profile  206 , and oil recovery profile  208  is being produced to well group  204 . 
     In some embodiments, well group  202  may be used for injecting a miscible enhanced oil recovery agent, and well group  204  may be used for producing oil and/or gas from the formation for a first time period; then well group  204  may be used for injecting a miscible enhanced oil recovery agent, and well group  202  may be used for producing oil and/or gas from the formation for a second time period, where the first and second time periods comprise a cycle. 
     In some embodiments, multiple cycles may be conducted which include alternating well groups  202  and  204  between injecting a miscible enhanced oil recovery agent, and producing oil and/or gas from the formation, where one well group is injecting and the other is producing for a first time period, and then they are switched for a second time period. 
     In some embodiments, a cycle may be from about 12 hours to about 1 year, or from about 3 days to about 6 months, or from about 5 days to about 3 months. In some embodiments, each cycle may increase in time, for example each cycle may be from about 5% to about 10% longer than the previous cycle, for example about 8% longer. 
     In some embodiments, a miscible enhanced oil recovery agent or a mixture including a miscible enhanced oil recovery agent may be injected at the beginning of a cycle, and an immiscible enhanced oil recovery agent or a mixture including an immiscible enhanced oil recovery agent may be injected at the end of the cycle. In some embodiments, the beginning of a cycle may be the first 10% to about 80% of a cycle, or the first 20% to about 60% of a cycle, the first 25% to about 40% of a cycle, and the end may be the remainder of the cycle. 
     Referring now to  FIG. 2   c , in some embodiments, array of wells  200  is illustrated. Array  200  includes well group  202  (denoted by horizontal lines) and well group  204  (denoted by diagonal lines). 
     In some embodiments, a miscible enhanced oil recovery agent is injected into well group  204 , and oil is recovered from well group  202 . As illustrated, the miscible enhanced oil recovery agent has injection profile  208  with overlap  210  with oil recovery profile  206 , which is being produced to well group  202 . 
     In some embodiments, a miscible enhanced oil recovery agent is injected into well group  202 , and oil is recovered from well group  204 . As illustrated, the miscible enhanced oil recovery agent has injection profile  206  with overlap  210  with oil recovery profile  208 , which is being produced to well group  204 . 
     Enhanced Oil Recovery Methods 
     The recovery of oil and/or gas with array of wells  200  from an underground formation may be accomplished by any known method. Suitable methods include subsea production, surface production, primary, secondary, or tertiary production. The selection of the method used to recover the oil and/or gas from the underground formation is not critical. 
     In some embodiments, oil and/or gas may be recovered from a formation into a well, and flow through the well and flowline to a facility. In some embodiments, enhanced oil recovery, with the use of an agent for example steam, water, a surfactant, a polymer flood, and/or a miscible agent such as a dimethyl ether formulation or carbon dioxide, may be used to increase the flow of oil and/or gas from the formation. 
     Releasing at least a portion of the miscible enhanced oil recovery agent and/or other liquids and/or gases may be accomplished by any known method. One suitable method is injecting the miscible enhanced oil recovery formulation into a single conduit in a single well, allowing dimethyl ether formulation to soak, and then pumping out at least a portion of the dimethyl ether formulation with gas and/or liquids. Another suitable method is injecting the miscible enhanced oil recovery formulation into a first well, and pumping out at least a portion of the miscible enhanced oil recovery formulation with gas and/or liquids through a second well. The selection of the method used to inject at least a portion of the miscible enhanced oil recovery formulation and/or other liquids and/or gases is not critical. 
     In some embodiments, the miscible enhanced oil recovery formulation and/or other liquids and/or gases may be pumped into a formation at a pressure up to the fracture pressure of the formation. 
     In some embodiments, the miscible enhanced oil recovery formulation may be mixed in with oil and/or gas in a formation to form a mixture which may be recovered from a well. In some embodiments, a quantity of the miscible enhanced oil recovery formulation may be injected into a well, followed by another component to force the formulation across the formation. For example air, water in liquid or vapor form, carbon dioxide, other gases, other liquids, and/or mixtures thereof may be used to force the miscible enhanced oil recovery formulation across the formation. 
     In some embodiments, the miscible enhanced oil recovery formulation may be heated prior to being injected into the formation to lower the viscosity of fluids in the formation, for example heavy oils, paraffins, asphaltenes, etc. 
     In some embodiments, the miscible enhanced oil recovery formulation may be heated and/or boiled while within the formation, with the use of a heated fluid or a heater, to lower the viscosity of fluids in the formation. In some embodiments, heated water and/or steam may be used to heat and/or vaporize the miscible enhanced oil recovery formulation in the formation. 
     In some embodiments, the miscible enhanced oil recovery formulation may be heated and/or boiled while within the formation, with the use of a heater. One suitable heater is disclosed in copending U.S. patent application Ser. No. 10/693,816, filed on Oct. 24, 2003, and having attorney docket number TH2557. U.S. patent application Ser. No. 10/693,816 is herein incorporated by reference in its entirety. 
     Referring now to  FIGS. 3   a  and  3   b , in some embodiments of the invention, system  300  is illustrated. System  300  includes underground formation  302 , underground formation  304 , underground formation  306 , and underground formation  308 . Facility  310  is provided at the surface. Well  312  traverses formations  302  and  304 , and has openings in formation  306 . Portions  314  of formation  306  may be optionally fractured and/or perforated. During primary production, oil and gas from formation  306  is produced into portions  314 , into well  312 , and travels up to facility  310 . Facility  310  then separates gas, which is sent to gas processing  316 , and liquid, which is sent to liquid storage  318 . Facility  310  also includes miscible enhanced oil recovery formulation storage  330 . As shown in  FIG. 3   a , miscible enhanced oil recovery formulation may be pumped down well  312  that is shown by the down arrow and pumped into formation  306 . Miscible enhanced oil recovery formulation may be left to soak in formation for a period of time from about 1 hour to about 15 days, for example from about 5 to about 50 hours. 
     After the soaking period, as shown in  FIG. 3   b , miscible enhanced oil recovery formulation and oil and/or gas is then produced back up well  312  to facility  310 . Facility  310  is adapted to separate and/or recycle miscible enhanced oil recovery formulation, for example by boiling the formulation, condensing it or filtering or reacting it, then re-injecting the formulation into well  312 , for example by repeating the soaking cycle shown in  FIGS. 3   a  and  3   b  from about 2 to about 5 times. 
     In some embodiments, miscible enhanced oil recovery formulation may be pumped into formation  306  below the fracture pressure of the formation, for example from about 40% to about 90% of the fracture pressure. 
     In some embodiments, well  312  as shown in  FIG. 3   a  injecting into formation  306  may be representative of a well in well group  202 , and well  312  as shown in  FIG. 3   b  producing from formation  306  may be representative of a well in well group  204 . 
     In some embodiments, well  312  as shown in  FIG. 3   a  injecting into formation  306  may be representative of a well in well group  204 , and well  312  as shown in  FIG. 3   b  producing from formation  306  may be representative of a well in well group  202 . 
     Referring now to  FIG. 3   c , in some embodiments of the invention, system  400  is illustrated. System  400  includes underground formation  402 , formation  404 , formation  406 , and formation  408 . Production facility  410  is provided at the surface. Well  412  traverses formation  402  and  404  has openings at formation  406 . Portions of formation  414  may be optionally fractured and/or perforated. As oil and gas is produced from formation  406  it enters portions  414 , and travels up well  412  to production facility  410 . Gas and liquid may be separated, and gas may be sent to gas storage  416 , and liquid may be sent to liquid storage  418 . Production facility  410  is able to produce and/or store miscible enhanced oil recovery formulation, which may be produced and stored in production/storage  430 . Dimethyl ether, diethyl ether, and/or other ethers from well  412  may be sent to miscible enhanced oil recovery formulation production/storage  430 . Miscible enhanced oil recovery formulation is pumped down well  432 , to portions  434  of formation  406 . Miscible enhanced oil recovery formulation traverses formation  406  to aid in the production of oil and gas, and then the miscible enhanced oil recovery formulation, oil and/or gas may all be produced to well  412 , to production facility  410 . Miscible enhanced oil recovery formulation may then be recycled, for example by boiling the formulation, condensing it or filtering or reacting it, then re-injecting the formulation into well  432 . 
     In some embodiments, a quantity of miscible enhanced oil recovery formulation or miscible enhanced oil recovery formulation mixed with other components may be injected into well  432 , followed by another component to force miscible enhanced oil recovery formulation or miscible enhanced oil recovery formulation mixed with other components across formation  406 , for example air; water in gas or liquid form; water mixed with one or more salts, polymers, and/or surfactants; carbon dioxide; other gases; other liquids; and/or mixtures thereof. In some embodiments, well  412  which is producing oil and/or gas is representative of a well in well group  202 , and well  432  which is being used to inject miscible enhanced oil recovery formulation is representative of a well in well group  204 . 
     In some embodiments, well  412  which is producing oil and/or gas is representative of a well in well group  204 , and well  432  which is being used to inject miscible enhanced oil recovery formulation is representative of a well in well group  202 . 
     Referring now to  FIG. 4 , in some embodiments of the invention, method  500  is illustrated. Method  500  includes injecting a miscible enhanced oil recovery formulation indicated by checkerboard pattern; injecting an immiscible enhanced oil recovery formulation indicated by diagonal pattern; and producing oil and/or gas from a formation indicated by white pattern. 
     Injection and production timing for well group  202  is shown by the top timeline, while injection and production timing for well group  204  is shown by the bottom timeline. 
     In some embodiments, at time  520 , miscible enhanced oil recovery formulation is injected into well group  202  for time period  502 , while oil and/or gas is produced from well group  204  for time period  503 . Then, miscible enhanced oil recovery formulation is injected into well group  204  for time period  505 , while oil and/or gas is produced from well group  202  for time period  504 . This injection/production cycling for well groups  202  and  204  may be continued for a number of cycles, for example from about 5 to about 25 cycles. 
     In some embodiments, at time  530 , there may be a cavity in the formation due to oil and/or gas that has been produced during time  520 . During time  530 , only the leading edge of cavity may be filled with a miscible enhanced oil recovery formulation, which is then pushed through the formation with an immiscible enhanced oil recovery formulation. Miscible enhanced oil recovery formulation may be injected into well group  202  for time period  506 , then immiscible enhanced oil recovery formulation may be injected into well group  202  for time period  508 , while oil and/or gas may be produced from well group  204  for time period  507 . Then, miscible enhanced oil recovery formulation may be injected into well group  204  for time period  509 , then immiscible enhanced oil recovery formulation may be injected into well group  204  for time period  511 , while oil and/or gas may be produced from well group  202  for time period  510 . This injection/production cycling for well groups  202  and  204  may be continued for a number of cycles, for example from about 5 to about 25 cycles. 
     In some embodiments, at time  540 , there may be a significant hydraulic communication between well group  202  and well group  204 . Miscible enhanced oil recovery formulation may be injected into well group  202  for time period  512 , then immiscible enhanced oil recovery formulation may be injected into well group  202  for time period  514  while oil and/or gas may be produced from well group  204  for time period  515 . The injection cycling of miscible and immiscible enhanced oil recovery formulations into well group  202  while producing oil and/or gas from well group  204  may be continued as long as desired, for example as long as oil and/or gas is produced from well group  204 . 
     In some embodiments, periods  502 ,  503 ,  504 , and/or  505  may be from about 6 hours to about 10 days, for example from about 12 hours to about 72 hours, or from about 24 hours to about 48 hours. 
     In some embodiments, each of periods  502 ,  503 ,  504 , and/or  505  may increase in length from time  520  until time  530 . 
     In some embodiments, each of periods  502 ,  503 ,  504 , and/or  505  may continue from time  520  until time  530  for about 5 to about 25 cycles, for example from about 10 to about 15 cycles. 
     In some embodiments, period  506  is from about 10% to about 50% of the combined length of period  506  and period  508 , for example from about 20% to about 40%, or from about 25% to about 33%. 
     In some embodiments, period  509  is from about 10% to about 50% of the combined length of period  509  and period  511 , for example from about 20% to about 40%, or from about 25% to about 33%. 
     In some embodiments, the combined length of period  506  and period  508  is from about 2 days to about 21 days, for example from about 3 days to about 14 days, or from about 5 days to about 10 days. 
     In some embodiments, the combined length of period  509  and period  511  is from about 2 days to about 21 days, for example from about 3 days to about 14 days, or from about 5 days to about 10 days. 
     In some embodiments, the combined length of period  512  and period  514  is from about 2 days to about 21 days, for example from about 3 days to about 14 days, or from about 5 days to about 10 days. 
     In some embodiments, oil and/or gas produced may be transported to a refinery and/or a treatment facility. The oil and/or gas may be processed to produced to produce commercial products such as transportation fuels such as gasoline and diesel, heating fuel, lubricants, chemicals, and/or polymers. Processing may include distilling and/or fractionally distilling the oil and/or gas to produce one or more distillate fractions. In some embodiments, the oil and/or gas, and/or the one or more distillate fractions may be subjected to a process of one or more of the following: catalytic cracking, hydrocracking, hydrotreating, coking, thermal cracking, distilling, reforming, polymerization, isomerization, alkylation, blending, and dewaxing. 
     Enhanced Oil Recovery Agents 
     In some embodiments, oil and/or gas may be recovered from a formation with methanol and/or one or more methanol derivatives, such as dimethyl ether, acetic acid, formaldehyde, and olefins, other ethers such as methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME) and the like, dimethoxy methane, polydimethoxy methane, and other chemical products produced from methanol, hereinafter referred to as a methanol compound. The methanol compound may include dimethyl ether. 
     In some embodiments, oil and/or gas may be recovered from a formation with nitrogen; glycols, such as mono-ethylene glycol, di-ethylene glycol, tri-ethylene glycol, and tetra-ethylene glycol; ethanol, methanol, or other alcohols; acetals; polyols; and/or one or more methanol derivatives, such as dimethyl ether, and/or one or more ethanol derivatives, such as diethyl ether. 
     In some embodiments, a hydrocarbon from the formation may be converted into a dimethyl ether formulation. The conversion of at least a portion of the hydrocarbon into a dimethyl ether formulation may be accomplished by any known method. Suitable methods may include reacting steam and natural gas at high temperatures and moderate pressures over a reduced nickel-containing catalyst so as to produce synthesis gas, where the natural gas may contain C1 to C6 compounds, such as C1 to C4 compounds. The synthesis gas production may be sent to a methanol reactor to generate methanol, which can be dehydrated to generate the dimethyl ether formulation. The selection of the method used to convert at least a portion of the hydrocarbon into a dimethyl ether formulation is not critical. 
     U.S. Pat. Nos. 7,168,265, 7,100,692, and 7,083,662 disclose the production of dimethyl ether from natural gas. U.S. Pat. Nos. 7,168,265, 7,100,692, and 7,083,662 are herein incorporated by reference in their entirety. In some embodiments, a suitable miscible enhanced oil recovery agent may be a dimethyl ether formulation. The dimethyl ether formulation may include dimethyl ether and/or dimethyl ether derivatives and/or precursors for example, methanol and mixtures thereof; and optionally one or more of the following: carbon dioxide, C1-C6 hydrocarbons, water, nitrogen, and mixtures thereof. In some embodiments, suitable miscible enhanced oil recovery agents include dimethyl ether, hydrogen sulfide, carbon dioxide, octane, pentane, LPG, C2-C6 aliphatic hydrocarbons, nitrogen, diesel, mineral spirits, naptha solvent, asphalt solvent, kerosene, acetone, xylene, trichloroethane, or mixtures of two or more of the preceding, or other miscible enhanced oil recovery agents as are known in the art. In some embodiments, suitable miscible enhanced oil recovery agents are first contact miscible or multiple contact miscible with oil in the formation. 
     In some embodiments, suitable immiscible enhanced oil recovery agents include water in gas or liquid form, air, nitrogen, mixtures of two or more of the preceding, or other immiscible enhanced oil recovery agents as are known in the art. In some embodiments, suitable immiscible enhanced oil recovery agents are not first contact miscible or multiple contact miscible with oil in the formation. 
     In some embodiments, immiscible and/or miscible enhanced oil recovery agents injected into the formation may be recovered from the produced oil and/or gas and re-injected into the formation. 
     In some embodiments, oil as present in the formation prior to the injection of any enhanced oil recovery agents has a viscosity of at least about 0.01 centipoise, or at least about 0.1 centipoise, or at least about 0.5 centipoise, or at least about 1 centipoise, or at least about 2 centipoise, or at least about 5 centipoise. In some embodiments, oil as present in the formation prior to the injection of any enhanced oil recovery agents has a viscosity of up to about 500 centipoise, or up to about 100 centipoise, or up to about 50 centipoise, or up to about 25 centipoise. 
     Illustrative Embodiments 
     In one embodiment of the invention, there is disclosed a system for producing oil and/or gas from an underground formation including a well above the formation; a mechanism to inject an enhanced oil recovery formulation into the formation, the enhanced oil recovery formulation including dimethyl ether; and a mechanism to produce oil and/or gas from the formation. In some embodiments, the system also includes a second well a distance from the first well, wherein the mechanism to produce oil and/or gas from the formation is located at the second well. In some embodiments, the underground formation is beneath a body of water. In some embodiments, the system also includes a mechanism for injecting an immiscible enhanced oil recovery formulation into the formation, after the miscible enhanced oil recovery formulation has been released into the formation. In some embodiments, the enhanced oil recovery formulation further comprises one or more of hydrogen sulfide, carbon dioxide, octane, pentane, LPG, C2-C6 aliphatic hydrocarbons, nitrogen, diesel, mineral spirits, naptha solvent, asphalt solvent, kerosene, acetone, xylene, trichloroethane, and mixtures thereof. In some embodiments, the system also includes an immiscible enhanced oil recovery formulation selected from the group consisting of water in gas or liquid form, air, nitrogen, and mixtures thereof. In some embodiments, the well comprises an array of wells from 5 to 500 wells. In some embodiments, the mechanism to produce oil and/or gas from the formation is located at the well. In some embodiments, the system also includes a mechanism for producing a dimethyl ether formulation adjacent to the well. In some embodiments, the underground formation comprises an oil having a viscosity from 0.01 to 5,000,000 centipoise. 
     In one embodiment of the invention, there is disclosed a method for producing oil and/or gas including injecting a dimethyl ether formulation into a formation for a first time period from a first well; and producing oil and/or gas from the formation from a second well. In some embodiments, the method also includes recovering dimethyl ether formulation from the oil and/or gas, if present, and then injecting at least a portion of the recovered dimethyl ether formulation into the formation. In some embodiments, injecting the dimethyl ether formulation comprises injecting at least a portion of the dimethyl ether formulation into the formation in a mixture with one or more of hydrocarbons other than dimethyl ether; carbon dioxide; carbon monoxide; or mixtures thereof. In some embodiments, the method also includes heating the dimethyl ether formulation prior to injecting the dimethyl ether formulation into the formation, or while within the formation. In some embodiments, the dimethyl ether formulation is injected at a pressure from 0 to 37,000 kilopascals above the initial reservoir pressure, measured prior to when dimethyl ether injection begins. In some embodiments, the underground formation comprises a permeability from 0.0001 to 15 Darcies, for example a permeability from 0.001 to 1 Darcy. In some embodiments, the method also includes converting at least a portion of the recovered oil and/or gas into a material selected from the group consisting of transportation fuels such as gasoline and diesel, heating fuel, lubricants, chemicals, and/or polymers. In some embodiments, the method also includes converting at least a portion of the recovered oil and/or gas into dimethyl ether, and injecting the dimethyl ether into an underground formation. 
     Those of skill in the art will appreciate that many modifications and variations are possible in terms of the disclosed embodiments of the invention, configurations, materials and methods without departing from their spirit and scope. Accordingly, the scope of the claims appended hereafter and their functional equivalents should not be limited by particular embodiments described and illustrated herein, as these are merely exemplary in nature.