Remote preheat and pad steam generation

Abstract

Methods and systems generate steam for injection in a well to facilitate oil recovery. Water is preheated at a central processing facility, transported to a well pad by hot water lines, and converted to steam by a steam generator at the well pad.

Claims

1. A method of generating steam for use in a well to produce oil, said method comprising: a) heating a boiler feedwater located at a central processing facility (CPF) to produce heated boiler feedwater (HBFW); b) transporting said HBFW to a well pad via hot water lines, wherein said HBFW has a subcool of 5-30 C.; c) feeding said HBFW into a well pad boiler located at said well pad; d) converting said HBFW to steam in said well pad boiler; and e) injecting said steam into a well located at said well pad to produce oil.

2. The method of claim 1, wherein said pad boiler is a water tube drum boiler.

3. The method of claim 1, wherein said heating step a) is by a gas burning water heater.

4. The method of claim 1, wherein said heating step a) is by a gas burning turbine heater that produces electricity and HBFW.

5. The method of claim 1, wherein said heating step a) is by a once through steam generator (OTSG).

6. The method of claim 1, wherein said heating step a) is preceded by a preheating step to preheat said boiler feedwater.

7. The method of claim 1, wherein said feeding step c) is preceded by a preheating step to preheat said HBFW.

8. The method of claim 1, wherein said heating step a) is preceded by a preheating step to preheat said boiler feedwater and wherein said feeding step c) is preceded by a preheating step to preheat said HBFW.

9. The method of claim 1, wherein said subcool is 10-20 C.

10. A steam generator system for oil production, comprising: a) a water heater located at a CPF to heat boiler feedwater to HBFW, said HBFW having a subcool of 5-30 C.; b) a hot water line for transporting said HBFW with a subcool of 5-30 C. from said CPF to a well pad; c) a steam generator located at said well pad, said steam generator being fed by said hot water line; d) a steam line for injecting steam into a well at said well pad; and, e) wherein elements a though d are fluidly connected.

11. The steam generator system of claim 10, further comprising a heat exchanger located at said CPF for preheating said boiler feedwater.

12. The steam generator system of claim 10, further comprising a heat exchanger located at said well pad for preheating said HBFW.

13. The steam generator system of claim 10, further comprising a heat exchanger located at said CPF for preheating said boiler feedwater and a heat exchanger located at said well pad for preheating said HBFW.

14. The steam generator system of claim 10, wherein said steam generator is a water tube drum boiler.

15. The steam generator system of claim 10, wherein said water heater is a gas turbine water heater.

16. The steam generator system of claim 10, wherein said water heater is an OTSG.

17. The steam generator system of claim 10, wherein said water heater is a gas fired water heater.

18. The steam generator system of claim 10, wherein said water heater is a natural gas fired water heater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A. provides one example of a water tube drum boiler.

(2) FIG. 1B. illustrates the operating principle for an OTSG.

(3) FIG. 2. One embodiment of the disclosed method using preheated well pad steam generator concept, with heat provided by steam generators at CPF.

(4) FIG. 3. Another embodiment of the disclosed method using preheated well pad steam generator concept, with heat provided by fired heater at CPF.

(5) FIG. 4. Another embodiment using preheated well pad steam generator concept, with heat provided by gas turbine exhaust gas.

DETAILED DESCRIPTION

(6) We investigated various alternatives for reducing the cost of steam generation without overcrowding the well pad, and herein describe a method wherein water is heated at the CPF to within 5-30 C. or 10-20 C. of the boiling point at the operating pressure of the OTSG or other steam generator.

(7) The subcooled water is transported to the well pad, where it is converted to steam in an OTSG, water tube drum boiler, or other boiler. If desired, the OTSG can be equipped with an economizer to capture waste heat from the blow-down water, produced fluids or waste flue gas. Because the feedwater is significantly preheated before transport to the OTSG, less fuel is used to create the steam. Further, the lines need only be qualified for hot fluid transport, not steam transport and thus need not meet the elevated temperature tensile tests and other high standards required for high pressure steam lines. In some embodiments, a distance of at least 100 meter or at least 1 kilometer separates the CPF from the well pad with the steam generator.

(8) FIG. 2 shows one embodiment of the disclosure wherein OTSG 1000 is at the CPF and functions (in part) to preheat water for a drum boiler 1500 at the well-pad. Two options are thus shown in FIG. 2. First, where the pad boiler feedwater is heated in a coil within an OTSG economizer section. This uses some of the thermal duty of the OTSG to provide feed water preheating, but requires a customized OTSG that can generate steam from one water source and preheat water from a second water source. In the second option, the well pad boiler feedwater is heated by heat exchange with the hot OTSG blowdown. This enables the use of existing OTSGs, but will impact the OTSG heat recovery system because blowdown heat that otherwise preheats OTSG feedwater is now used to heat pad boiler feedwater. One or the other or even both systems could be used.

(9) In more detail, air entering the OTSG via line 190 is preheated in heat exchanger 1060. Fuel enters the burner 1010 via line 180, mixes with preheated air from line 190 and burns to create hot gas, which travels to the other end of the OTSG heating fluid in coils 100 and 101. The hot gas pathway is from the burners to the stack. Coil 101 accepts boiler feedwater via line 130, which is preheated with blowdown water and coil 100 accepts boiler feedwater via line 110. The routing of these lines is of course variable, as noted above, depending on which option(s) is/are implemented. Hot gas that has given its latent heat to the fluid in the coils 100, 101 can be routed back to heat exchanger 1060 if desired. Alternatively, it can be routed to the stack.

(10) Hot fluid exiting OTSG coils is routed to separator 1030 via line 150, where steam is separated from blow-down water. Steam is routed via line 160 to where its is needed, e.g., to the well pad for injection, and blowdown water run through line 170 to heat exchanger 1050 to warm incoming boiler feedwater via line 130. Preheated water can be routed via line 140 and pump 1040 to the well pad for use in drum boiler 1500.

(11) Subcooled water enters the drum boiler 1500 at the well pad via line 140, is turned into steam in drum boiler 1500 and the steam routed to the well via steam line 240. Fuel enters a burner 1530 of drum boiler 1500 via fuel line 230, and heated air via line 220. The air from line 210 was preheated in air preheater (heat exchanger) 1510 using the exiting flue gas.

(12) FIG. 3 shows yet another embodiment, using a natural gas (NG) fired water heater 2000 at the CPF to preheat water for the steam generator at the well pad, in this case water tube drum boiler 2500. If desired, clean water (e.g., from an evaporator) via line 210 can be preheated with heat exchanger 2060, e.g, by hot glycol originating from e.g., the CPF hot glycol system (i.e. glycol that has been heated in various units that cool process streams). The water can be further heated using produced fluids from the reservoir after separation in a pad separator 2070, using gas heat exchanger 2030 via line 216 for a first portion 213 of the water and liquid heat exchanger 2050 via line 215 for a second portion 211 of the water.

(13) The somewhat cooled produced liquid is then routed to a separator (not shown) for separation into crude oil, routed to storage or shipment, and produced water, which is routed to water treatment facilities, in this instance suggesting an evaporator, but possibly including one or more of filtration, precipitation, warm lime softener, an advanced oxidation process, and the like.

(14) Prewarmed water is routed via line 214 to a water heater 2000, e.g, a NG fired water heater with burner 2010 fed by air and fuel lines. Hot water is transported to the well pad by pump 2550. If desired that water was can also be heated in heat exchanger 2560 by blowdown water fed by line 219. Blowdown water then travels by line 220 to some water treatment facility.

(15) Preheated water enters drum boiler 2500 via line 218. Drum boiler 2500 is heated by burner 2510 fed by air line 224 and fuel line 223. Air line 224 can be preheated in air preheater 2540, which is heated with hot flue gas exiting the drum boiler 2500 via line 225.

(16) Steam exits the drum boiler 2500 via lines 220 and 222 to separator 2520 which sends water back to the drum boiler 2500 via line 220 and pump 2530 and steam to the well via line 221. The steam in lines 220 appears to be running in two directions due to the internal recirculation in water tube drum boilers. Drum boilers inherently have high internal recirculation rates, i.e. only 10-20% of the feedwater is evaporated in boiler. The 10-20% quality steam enters a drum to separate steam/water, and the water is recirculated.

(17) FIG. 4 shows yet another possible embodiment, wherein a gas turbine 3010 generates heat and electricity (not shown) for use on site, by burning air routed through compressor 3030 in combustor 3020 fed by fuel line 315 and air line 314. The burning fuel rotates the turbine 3010 and the hot gases used to preheat water in heat exchanger 3000, and exit via turbine exhaust line 316. As in FIG. 3, the water entering heat exchanger 3000 can be preheated by a variety of hot fluids readily available at the pad, further improving efficiency. The remainder of FIG. 4 is similar to FIG. 3, having a number of heat exchangers (3040, 3050, 3060, 3530, 3550), pumps (3540, 3510), air (312, 314) and fuel lines (311, 315), feedwater lines (306, 307, 308, 309), separators (3520, 3070), blowdown water line 310, produced gas line 305, produced liquid line 303 and drum boiler 3500 which accepts the remotely preheated water as a boiler feedwater, and uses burner 3560 to produce the hot gas that turns the heated feedwater to steam and is exhausted via line 313.