Continuous tracer generation apparatus

Description of equivalent WO 2004023096 A2

PATENT APPLICAΗON OF DENNIS D. COLEMAN, RODNEY R. RUCH, SHIAOGUO CHEN AND MASSOUD ROSTAM-ABADI

FOR

TITLE: CONTINUOUS TRACER GENERATION APPARATUS

CROSS REFERENCE TO RELATED APPLICAΗON: This application claims the benefit of PPA Application Number 60/317,702 with a filing date of 09/07/2001.

FEDERALLY SPONSOREDRESEARCH Not applicable. SEQUENCE LISTING OR PROGRAM Not applicable. BACKGROUND

This invention relates to an on-site, continuous method of tracer generation that can be utilized to tag natural gas. Natural gas is composed primarily of methane but contains lesser proportions of many compounds, Notable among those compounds are ethane, propane, and higher hydrocarbons. Although this invention finds application in tagging natural gas feedstock, it can be used to tag many other carbonaceous compounds including pure methane. Feedstock as used in this application encompasses natural gas, pure methane, the components of natural gas such as ethane, or any other carbonaceous substance in either liquid or gaseous form. Most of the natural gas that is used in North America is produced either in the Gulf Coast region or in Northwestern Canada. Yet, most of the gas is used in the Northeast, the Midwest, and the northwestern United States. Therefore, large pipelines crisscross the country to transport natural gas from the producing areas to areas where the gas is used. Natural gas is frequently a byproduct of oil production. To produce oil, one often must also produce natural gas. Thus natural gas is produced year round in oil producing areas. However, there are also areas, which produce only natural gas, without oil. In those areas it is necessary to produce gas continuously, at a controlled rate, to maximize the productivity of a gas field. Further, if gas or oil is produced too rapidly, it can result in groundwater being drawn into the well and can seriously damage or even destroy a well. Because gas is produced throughout the year but used primarily during the winter months, it is necessary to store natural gas until the months of peak usage. The most common method of storing natural gas is in underground storage reservoirs. Many of these storage reservoirs are areas where natural gas was produced years before. Because these reservoirs were demonstrated to have contained natural gas for millions of years, they provide a natural storage mechanism. Underground storage fields generally consist of porous rocks that are overlain by non-porous and non-permeable rocks. The porous rocks generally have the pore space filled with water. If one drills through the non- porous overlaying rock, or cap rock, one can pump gas into the pore space of the underlying reservoir unit, displacing the water. 77 There are over 350 such underground storage fields in North America in which

78 gas is pumped underground during the warmer months of the year, and then withdrawn

79 when additional gas is needed during cold periods. Some of these reservoirs are near the

80 producing areas and others are near the end markets, sometimes in populated areas.

81 Although underground storage reservoirs are designed to contain the gas, leakage of gas

82 from these reservoirs does sometimes occur, resulting in a loss to the owner.

83 There are many scenarios in which identification of gas that has leaked or has

84 been removed from a storage reservoir is critical. For example, if gas migrates to the

85 surface it can enter shallow groundwater, used for drinking water supplies, and can even

86 come to the surface, enter buildings, and result in explosions. Whenever natural gas is

87 detected in the near-surface environment, over or near a gas storage reservoir, it becomes

88 critical to determine if it is naturally occurring, native gas, or if it is gas leaking from the

89 storage reservoir.

90 Another setting in which gas identification is critical is when there are producing

91 oil and/or gas wells near gas storage fields. There are numerous situations throughout

92 North America where this is the case. Although a gas company may attempt to define

93 and describe the limits of the underground storage reservoir, the natural variations in the

94 earth structure make it extremely difficult to be precise. Thus when gas is produced from

95 a horizon above or adjacent to a gas storage field, the question frequent arises as to the

96 ownership of that gas. If the gas occurs naturally within the rocks, it is the property of

97 the producer. However, if the gas has migrated from a gas storage field, depending upon

98 local laws, it may remain the property of the gas company. There have been numerous

99 disputes throughout the country over the ownership of natural gas.

100 Thus, the ability to tag natural gas and the consequent capability of identifying the

101 owner of the gas, is of significant value. To identify the source of natural gas, a tracer

102 (like a fingerprint) may be added to the stored natural gas. By detecting the tracer

103 contained in the gas under investigation, one could trace it back to its source. To qualify,

104 the tracer has to satisfy several criteria: a), it must not normally exist in natural gas; b).

105 it should not segregate from stored natural gas; c). it should not decompose rapidly or

106 react with any other components; d). it should not be absorbed by the aquifer; and e). the 107 detection limit should be low (that is the resolution should be high), so that the amount of

108 added tracer can be low.

109 Natural gas within distribution pipelines in the country is tagged by adding an

1 10 odorant. This is generally a sulfur bearing mercaptan. Because these mercaptans do no

111 normally exist within natural gas, the presence of a mercaptan within the gas identifies it

112 as pipeline gas. In gas storage reservoirs, mercaptans cannot be used effectively as 13 tracers because, among other reasons, they are very reactive with the rocks. The gas may 14 contain mercaptans when it is injected into a reservoir, but that mercaptan can quickly 15 disappear and not remain with the gas. There are no existing methods of tagging gas 16 prior to gas storage that are simple enough and inexpensive enough to be used on a 17 routine basis as is done for pipeline gas distribution systems. 18 Many tracers have been tried, including ethylene, propylene, hydrogen, carbon 19 monoxide, and others. Ethylene (C FL;) is one of the best tracers among all the tested 20 tracers because it satisfies all the requirements of a good tracer. Pure ethylene generated 21 offsite and shipped to the storage field has been used. Since the amount of natural gas to 22 be stored is huge, in the range of billions of cubic feet, the use of pure ethylene is too 23 expensive if it is used on a regular basis. Furthermore, commercially available quantities 24 of ethylene are either too large or too small and are thus not suited to continuous use in 25 tagging natural gas storage fields. This invention produces ethylene and other potential 26 tracers at a low cost and in quantities ideal for tagging natural gas with this tracer. 27 Although there have been several other tracers developed which can be utilized in 28 gas reservoir studies for various purposes, there are none without serious limitation. For 29 example, U. S. Pat. 4, 551,154 to Malcosky describes an approach where the chemical 30 sulfur hexafluoride and/or chloropentafluoroethane is injected into gas fields to determine 31 ownership. Field tests have indicated that the two compounds were not fully recovered 32 whereas as tracers such as ethylene, were fully recovered. The two tracers appeared to be 33 less mobile than ethylene. Low permeability structures could restrict the migration of 34 these compounds. Further, this system utilizes very expensive chemicals and specialized 35 analytical equipment. Other authorities have determined that sulfur hexafluoride was not 36 deemed to be a suitable tracer in this application due to its instability and reactivity under 37 long-term field conditions and its differing dispersion behavior relative to methane, while 138 yet other authorities maintain that sulfur hexafluoride may have toxicity problems that

139 may preclude its extensive utilization.

140

141 OBJECTS AND ADVANTAGES

142

143 The invention uses materials to generate the tracer that are all readily available

144 and inexpensive, i.e., the primary components of natural gas itself. Most of the processes

145 that are used to generate ethylene or propylene from natural gas use only heat (pyro lysis),

146 or at most, oxygen or water as the other reactant. Oxygen is of course readily available

147 from air. Therefore, the invention does not involve transporting reactants from some

148 great distance and is not hindered by commercially available quantities. With the use of

149 the proper reactor, the only other thing needed to generate a tracer from natural gas is

150 energy, which can even be supplied by combustion of a small amount of the natural gas

151 itself.

152 Pure ethylene can be used as a tracer, but because the amount of natural gas to be

153 stored is huge, the use of pure ethylene is too expensive if it is used on regular basis. A

154 new technology, which could produce ethylene and other potential tracers at a low cost is

155 needed. The invention described herein, provides an apparatus whereby tracer can be

156 added to natural gas continuously, and at very low cost. All current methods of adding

157 tracers to natural gas involve transporting pure or manufactured products to the point

158 where they can be introduced into the gas line. This invention allows on-site generation

159 of tracer.

160 The process generates compounds that are not normal constituents of natural gas

161 and that have been previously verified as usable tracers within the gas storage industry.

162 More specific tracers can be generated by utilizing water that is enriched in deuterium,

163 tritium, oxygen- 18, or other isotopic species. The process, being either pyro lysis or the

164 catalytic reaction of air, carbon dioxide or water with natural gas, is such that the

165 necessary, commercially available equipment can be made transportable for easy

166 movement from one site to another.

167 The cost of this process is so low that it will be possible to routinely and

168 continuously tag all of the gas injected into a storage reservoir eliminating many of the

169 problems associated with existing tracer technology. Currently there are no tracers for 170 gas that is stored in underground reservoirs that can be economically utilized on a long

171 term, continuous basis.

172 The analytical equipment and methods necessary for analysis of the basic tracers

173 are those present in most laboratories capable of carrying out routine analysis of natural

174 gas, further adding to the economic benefits of this process.

175

176 SUMMARY 177

178 This invention is based on the discovery of a method of utilizing a feedstock,

179 itself, to generate identifying tracers through either a pyrolytic process or a reaction

180 process in the presence of certain catalysts. Ethylene is the primary tracer generated,

181 however, other tracers such as propylene, acetylene, H₂, CO, are also generated in the

182 reaction process or other tracers such as deuterated water and isotopically labeled

183 hydrocarbons can be introduced and can serve singly as tracers.

184 Accordingly, these tracers can be used in combination to produce readily

185 identifiable tracer mixtures that serve as unique markers. The invention not only creates

186 the tracers but creates the tracers in predetermined concentrations. Feedstock tagged with

187 predetermined concentrations can also serve as unique identifiers.

188 A further aspect of the invention is the on-site capability of tracer generation.

189 This allows entire storage fields to be continuously tagged at the time the fields are

190 initially filled or injected eliminating the need to acquire tracer in commercially

191 reasonable amounts and transporting those tracers to the field injection well.

192

193 BRIEF DESCRIPTION OF THE DRAWINGS

194

195 Figure I is a schematic diagram of the apparatus whereby ethylene tracer and other

196 desirable tracers are generated on-site and online and then reintroduced into the feedstock

197 to be stored.

198 Figure 2 is a schematic diagram of an alternative embodiment of the apparatus whereby

199 the pressure differential means is a choke valve.

200

201 REFERENCE NUMERALS

202

203 first line 1 204 storage field compressor 2

205 choke valve 2a

206 second line 3

207 first flow meter 4

208 twenty sixth line 5

209 third line 6

210 flow control and pressure reduction valve 7

211 fourth line 8

212 collector 9

213 fifth line 10

214 second flow meter 11

215 sixth line 12

216 heat exchanger 13

217 seventh line 14

218 first three-way valve 15

219 sixteenth line 15

220 seventeenth line 16

221 twenty second line 17

222 twenty seventh line 18

223 first valve 19

224 nineteenth line 21

225 second valve 22

226 eighth line 23

227 eighteenth line 24

228 twenty third line 25

229 third valve 26

230 twentieth line 27

231 fourth three-way valve 28

232 fourth valve 29

233 twenty eighth line 30

234 first primary reactor 32

235 second primary reactor 33

236 ninth line 34

237 twenty-first line 35

238 second three-way valve 36

239 twenty fifth line 37

240 reactant source 38

241 twenty third line 40

242 secondary reactor 41

243 tenth line 42

244 eleventh line 43

245 twelfth line 44

246 thirteenth line 45

247 third three-way valve 45a

248 fifteenth line 46

249 twenty ninth line 46a 250 fourteenth line 47 251 analyzer 48 252 fifth data line 49 253 fourth data line 50 254 sixth dataline 51 255 first data line 52 256 second data line 53 257 third data line 54 258 computer control 55 259 260 261 DETAILED DESCRIPTION 262

263 This invention utilizes several processes to generate ethylene tracer and other

264 secondary tracers. The processes are the oxidative coupling of methane (OCM) in natural

265 gas process and pyrolysis of ethane, a constituent of natural gas. For pyrolysis, both

266 atmospheric pressure and high-pressure conditions were studied. These two technologies

267 allow a cost-effective on-site and online process for underground gas storage use on a

268 regular basis. Furthermore, the process may also employ oxidative pyrolysis,

269 chloropyrolysis, steam and/or carbon dioxide reforming and partial oxidation of natural

270 gas and natural gas conversion using electric arc or plasma to generate such tracers as

271 acetylene, carbon monoxide, hydrogen, and isotopically labeled hydrocarbons

272 An experimental reaction system was designed for the OCM and pyrolysis 273 experiments. Separate sources for CHt, natural gas and air were fed into a central line 274 through individual flow meters. The central line then led to a heat source surrounding 275 the reactor. In the atmospheric pressure experiments, a quartz tube (7mm ID) was used 276 as the reactor with a heating zone approximately 30 cm long. In the pressurized 277 pyrolysis, a stainless steel tube (0.04 inch ID and ^lλ-\6 inch OD) was used. Here the 278 heating zone was also 30 cm long. In the latter system, a pressure release valve was used 279 to keep the system pressure at 850 psi. Actual pipeline gas was used but pure methane 280 was tested for comparison purposes. Table 1 illustrates the composition of methane and 281 the pipeline gas used.

282 Table t.

<img file="WO2004023096A2_D0001.tif" /><img file="WO2004023096A2_D0002.tif" />

283

284 Example 1

285 In the OCM process, methane, the major component of natural gas, is used as 286 feedstock to generate higher hydrocarbon compounds. The simplified chemistry of OCM 287 process is as follows : <img file="WO2004023096A2_D0003.tif" /> The oxygen can be from air or pure 288 oxygen gas. For the purposes of the invention, air is easier and cheaper to obtain. The 289 OCM process will utilize a catalyst that results in the production of ethylene as one of the 290 major C₂ products when the reaction is properly controlled. Since the OCM reaction is 291 very fast and strongly exothermic, only low oxygen concentrations can be applied. Thus 292 the concentration of ethylene in the product stream is usually low. It should be noted that 293 low concentration of product, added to the high cost of separating ethylene from the 294 product stream are factors that hinders the commercialization of OCM process for 295 ethylene production, but are not factors for the on-site production of tracer.

296 One catalyst studied was Mn/Na₂WO /SiO₂. Table 2 illustrates the yield of 297 ethylene in one sample of pure methane and one sample of natural gas (NG), both in the 298 presence of the Mn/Na₂WO₄/SiO₂ (LICP-1) catalyst.

299 Table 2.

<img file="WO2004023096A2_D0004.tif" />

300

301 These test results show the yield of ethylene from natural gas in the catalytic 302 process increased by more than two percent as compared to that observed for natural gas 303 in the non-catalytic process. 304 Example 2

305 Ethane pyrolysis is a well-established process. However, reaction kinetics have 306 been studied primarily with pure ethane (with steam) pyrolysis and at atmospheric 307 pressure. In order to obtain more realistic data, pyrolysis of real pipeline gas (NG) was 308 conducted at a total pressure of 1 atmosphere. Table 3 illustrates the results of ethylene 309 production at standard pressures using pipeline gas.

310 Table 3.

<img file="WO2004023096A2_D0005.tif" />

311

312 The results showed that at 900 °C about 70% of the ethane in the pipeline gas is 313 converted to ethylene. A small amount of acetylene is also formed, which can also be 314 used as a tracer. The results are in agreement with the results from theoretical prediction. 315 It can be seen in Table 3 that, as predicted by thermodynamics, higher temperature favors 316 the ethane pyrolysis reaction.

317 Example 3

318 Since pipeline gases are usually pressurized and the pressure of gas to be stored 319 underground is even higher, it would be desirable to convert ethane at an elevated 320 pressure, especially at or above the transportation pressure of pipeline gas. Most of the

321 pipeline gas has a pressure range from 600 psi to 850 psi, and 850 psi was chosen as the

322 test pressure. Table 4 illustrates the results of ethylene production at elevated pressures

323 similar to those seen in natural gas pipelines.

324 Table 4

<img file="WO2004023096A2_D0006.tif" />

325

326 The ethylene concentration in the product stream produced at high pressure was 327 lower than the ethylene concentration produced in the atmospheric system. This can be 328 explained by the effect of partial pressure of ethane in the system. Total pressure 329 adversely affects the equilibrium constant for ethane conversion. Increasing pressure 330 decreases the ethylene concentration. At 850 °C and at 850 psi, about 30% of ethane that 331 existed in pipeline natural gas is converted to ethylene, compared with 70% for the 332 atmospheric process. This is in agreement with the thermodynamics. At 850 °C, and 333 under optimized residence time, the maximum ethylene concentration is about 30% of the 334 ethane concentration in the feedstock. In this case ethane concentration in feedstock is 335 around 3.6 and the highest ethylene concentration in the test is 1.2 %. Ethane partial 336 pressure in the pressurized system is around 3.6%*850=30 psi, which is approximately 2 337 atm and is close to the pressure used in commercial processes. It should be noted as

338 illustrated in the last column, that propylene is also generated and this too can serve as a

339 tracer. Controlling the ethylene/propylene ratio provides a way of generating different

340 "signatures" in different gas streams. It is interesting to note that the optimized

341 conditions for maximizing ethylene concentration could be very close to the optimization

342 conditions for maximizing propylene concentration.

343 All mechanisms tested generated ethylene in sufficient quantities to allow a tracer

344 concentration of 50 to 100 parts per million to be generated in the post pyrolysis

345 feedstock to be introduced into the feedstock stream designated for injection.

346 Additional tracers can be generated post-pyrolysis by reforming reactions using

347 water and/or carbon dioxide or partial oxidation using air. Reforming reactions involving

348 the addition of heat, would follow the general formula 2H₂O + C₂H₆ =2CO + 5H₂ or

349 2CO + C₂H₆ =4CO + 3H₂. Oxidation reactions would follow the general formula O₂ +

350 C H₆ — 2CO + 3H₂. CO is not present in natural gas and can provide additional tracer

351 functions.

352 De-coking can also be accomplished by the addition of water, carbon dioxide and

353 air, pre-pyrolysis. The basic reactions would be as follows: H₂O + C=CO + H_2&gt; or CO₂

354 + C=2CO, and finally O₂ + C=2CO.

355 Turning to FIG. 1, it can be seen that carbonaceous feedstock, for example natural

356 gas, is introduced into the system through first line 1, in practice, a pipeline delivering

357 natural gas to a storage field. Pressures in Line 1 will usually be in the neighborhood of

358 600 to 850 psi. First line 1 enters and is fluidly connected storage field compressor 2

359 where the pressure of the natural gas is increased to allow injection into a storage field

360 reservoir. Pressures here may exceed 1750 psi.

361 Drawing feedstock from the feedstock source is accomplished by second line 3

362 that exits the storage field compressor and enters first flow meter 4 that measures the

363 flow rate within the feedstock source. A transducer in flow meter 4 will transmit data,

364 through first data line 52 to computer control 55 indicating the volume of feedstock

365 passing through flow meter 4. Twenty-sixth line 5 exist flow meter 4 and enters the

366 storage field. Third line 6 establishes fluid communication with the feedstock source and

367 removes feedstock under pressure to flow control and pressure reduction valve 7, also 368 fluidly connected to third line 6. Regulating flow and pressure thorough the fluid

369 communication is flow control and pressure reduction valve 7. Valve 7 is controlled

370 through second data line 53, which is connected to the computer control 55 and controls

371 the quantity and pressure of the gas passing valve 7. The flow control and pressure

372 reduction valve also will serve to reduce the variations in pressure, which may be induced

373 by the storage field compressor and is controlled by computer control 55, again through

374 second data line 53. Fourth line 8 then delivers feedstock to a collector 9 that cools the

375 feedstock within the fluid communication. Collector 9 is designed to cryogenically

376 precipitate certain classes of compounds such as butanes and pentanes, which contribute

377 to coking later in the process. Fifth line 10 then exits the collector 9 and enters second

378 flow meter 11. Second flow meter 11 measures the flow rate within the fluid

379 communication at this stage. Second flow meter 11 contains a transducer, which

380 transmits data, through third data line 54, to computer control 55, reporting the effects, on

381 the feedstock, of flow control and pressure reduction valve 7. Sixth line 12 exits second

382 flow meter 11 and enters heat exchanger 13. Heat exchanger 13 utilizes heat from

383 downstream feedstock exiting from a reaction zone to allow preheating of the feedstock

384 within the fluid communication which then enters the reaction zone of the reactors.

385 Preheating in heat exchanger 13 saves energy and reduces the time necessary for the

386 feedstock to remain within the reaction zone. Seventh line 14 exits heat exchanger 13

387 and enters first three-way valve 15. First three-way valve 15 directs the feedstock to

388 either first primary reactor 32 or second primary reactor 33. In FIG. 1, first three-way

389 valve 15 is diverting feedstock into second primary reactor 33 through eighth line 23 and

390 into second primary reactor 33 where ethane pyrolysis or oxidative coupling is

391 accomplished generating tracers within either the non-catalytic reaction zone or catalytic

392 reaction zone as the case may be. Ninth line 34 exits second primary reactor 33 to second

393 three-way valve 36. Tenth line 42 exits second three-way valve 36 and enters secondary

394 reactor 41. Secondary reactor 41 would allow introduction of reactants into the stream

395 and the production of secondary tracers. Eleventh line 43 exits secondary reactor 41 and

396 enters heat exchanger 13 where heat is transmitted to feedstock entering through sixth

397 line 12 raising the temperature of the feedstock that has not yet undergone reaction. 398 Twelfth line 44 exits the heat exchanger and reintroduces the product gas into first line 1

399 and the feedstock source

400 The post reaction analysis of the feedstock to determine trace levels is

401 accomplished when thirteenth line 45 diverts a sample of feedstock from twelfth line44

402 into third three-way valve 45a. Third three-way valve 45a then diverts feedstock in

403 thirteenth line 45 into fourteenth line 47 and consequently into analyzer 48. Thus a fluid

404 communication with post reaction feedstock is established. Introduction of the post

405 reaction feedstock into the analyzer is accomplished allowing the measure of tracer

406 levels. Analyzer 48, in this configuration, would be a gas analyzer such as a gas

407 chromatograph, mass spectrometer, infrared spectroscope or other analyzer of similar

408 capability. Analyzer 48 measures the level of tracer and transmits that information to

409 computer control 55 through fourth data line 50. Data establishing the desired level of

410 tracer concentration is introduced into the computer control 55 that has been programmed

411 to adjust the system to achieve a predetermined desired tracer concentration. Computer

412 control 55 consequently transmits flow and pressure regulating data within the fluid

413 communication and adjusts the flow rate through flow control and pressure reduction

414 valve 7 by transmitting data instructions through second data line 53. Adjusting the rate

415 of draw of feedstock into the system is initiated if the analysis reveals that tracer levels

416 are falling, computer control 55 then increases the amount of feedstock flowing through

417 flow control and pressure reduction valve 7 and, consequently, a greater amount of tracer

418 is generated bringing the tracer level up to the desired value. Three-way valve 45a also

419 will allow a sample to be taken through fifteenth line 46 of the feedstock in second line 3

420 emanating from the storage field compressor. Thus a fluid communication with pre

421 reaction feedstock is established. Introduction of the pre reaction feedstock into the

422 analyzer is accomplished allowing the measure of tracer levels at that point in the system.

423 Tracer levels within the post reaction feedstock and pre reaction feedstock are compared

424 with the predetermined desired tracer concentration. Software that could be utilized

425 could be programs such as "The Gas Flow Control System" by Zin Technologies or the

426 combined use of "Lookout" by National Instruments and "TLC Momentum from

427 Modocom Instruments. 428 Sixth dataline 51 connects third three-way valve 45a and computer control 55.

429 Computer control 55 will cause three-way valve 45a to continuously and alternately draw

430 samples from fourteenth line 45 and fifteenth line 46. As stated, fourteenth line 45 draws

431 product gas from first line 1, however, fifteenth line 46 will draw pre pyrolysis feedstock

432 from second line 3. Feedstock from second line 3 is continuously analyzed to determine

433 the level of tracer that has been introduced through fourteenth line 45 into first line 1.

434 Introducing the feedstock into a reaction zone is accomplished by first three-way

435 valve 15 being set to direct the feedstock flow from seventh line 14 into seventeenth line

436 16 and into first primary reactor 32. After remaining in the reaction zone for a

437 predetermined period of time, where the tracer is generated. Feedstock then exits through

438 eighteenth line 24 and into second three-way valve 36, which is set to accept feedstock

439 from eighteenth line 24 passing it on through to tenth line 42. In this way, the reaction

440 zone may be shifted from second primary reactor 33 to first primary reactor 32, thereby

441 taking second primary reactor offline to allow decoking. In this manner, second primary

442 reactor 33 and first primary reactor 32 may be alternately taken off line for maintenance,

443 component replacement and decoking. Decoking of the second primary reactor may be

444 accomplished by adjusting first three-way valve 15 and second three-way valve 36 to

445 place first primary reactor 32 online. Then, first valve 19 is closed and second valve 22

446 is opened. This will allow compressed air from compressed air source 20 to flow into

447 nineteenth line 21 and subsequently into twentieth line 27 and then into second primary

448 reactor 33 allowing coke burn off. At the same time third valve 26 is closed and fourth

449 valve 29 is open. Then the decoking product stream exits second primary reactor 33 via

450 ninth line 34, then enters twenty-first line 35, then into through fourth valve 29, into

451 twenty eighth line 30 and exits the system through vent 31.

452 Alternatively, first three-way valve 15 and second three-way valve 36 may be set

453 to allow the redirecting of the feedstock into second primary reactor 33. Second valve 22

454 is closed and first valve 19 is open. Thus, allowing compressed air to pass into

455 nineteenth line 21 and on into twenty second line 17, then into first primary reactor 32.

456 The combustion stream from decoking then exits first primary reactor 32 via eighteenth

457 line 24, then enters twenty third line 25 passing through open third valve 26 entering line 458 30, then closed fourth valve 29 will direct the combustion product to vent outside the

459 system through vent 31.

460 In order to facilitate decoking or to generate further secondary tracers, other

461 reactants may be introduced under pressure through reactant source 38. Reactant source

462 38 and the consequent introduction of reactants, is activated by computer control 55

463 through fifth data line 49. Should decoking be desired, compounds such as water, carbon

464 dioxide and air may be introduced. In this case, those compounds would exit reactant

465 source 38 into fourth three-way valve 28, which will be sent to empty into twenty third

466 line 40, which will then transmit the decoking compounds through seventh line 14 into

467 either the first primary reactor 32 or the second primary reactor 33. Alternatively, fourth

468 three-way valve 28 could be configured to introduce reactants from reactant source 38

469 into twenty fifth line 37, which will then be transferred into secondary reactor 41.

470 An alternative embodiment would be the use of a mechanism to generate pressure

471 differential such as a separate compressor, choke, or valve in place of the storage field

472 compressor, to cause flow through the reactor. As shown in FIG. 2, if a choke or valve is

473 used then the direction of flow in first line 1 and twenty sixth line 5 is reversed from that

474 shown in FIG. 1. In this embodiment twenty ninth line 46a takes the place of fifteenth

475 line 46 and connects to first line 1 down flow from choke valve 2a. If this embodiment is

476 used it would find application, for example, on an individual injection well which would

477 be located down flow from choke valve 2a as compared with the storage field being

478 down flow from the pressure differential means 2 in FIG. 1. Up flow from the choke

479 valve 2a would be the storage field compressor or feed line. Thus tracers can be injected

480 at several points to study the characteristics of a storage field.

481 Although the description above contains many detailed specifics, they should be

482 viewed as illustrative and not as limiting the scope of the invention which should be

483 determined by the claims and their legal equivalents.

484

485 486 487