The role of radiotracers in petroleum production

Transcription

1 The role of radiotracers in petroleum production - presentation at the TRACER-3 conference, Poland, June 21-25, 2004 Tor Bjørnstad Institute for Energy Technology (IFE) Kjeller, NORWAY Tor Bjørnstad 1

2 Outline Brief about petroleum production Phases in the petroleum industry with radiotracer assistance Summary - conclusion Tor Bjørnstad 2

3 Organic material Probably more from microscopic diatoms - - than from dinosaurs Tor Bjørnstad 3

4 Oil generation and migration Tor Bjørnstad 4

5 Geologic traps - faults 5-20,000 Oil trapped in domes or anticlines Tor Bjørnstad 5

6 3D seismic examination Tor Bjørnstad 6

7 Dynamite explosions or vibrator trucks are used to create the seismic waves. Geophones laid out in lines measure traveling time of the waves from seismic source, reflection off a rock boundary, and return to the geophone. The resulting two-dimensional image, which is called a seismic line, is essentially a crosssectional view of the earth oriented parallel to the line of geophones Seismic lines Tor Bjørnstad 7

8 Exploratory drilling Tor Bjørnstad 8

9 Oil & gas production (1) Oil production requires some type of drive to extract the oil from the source rock 1. Water Drive Tor Bjørnstad 9

10 Enhanced recovery Producing well Injector well Secondary recovery techniques involve augmenting the natural drive by injecting water (or gas) at the edges of the field Tor Bjørnstad 10

11 Pump-assisted oil recovery Pumps can assist in bringing oil to the surface, especially in shallow low-pressure land-based reservoirs. (Photo: Rotary pump operating at the Red River field in Saskatchewan) Tor Bjørnstad 11

12 Drill rig types 5,000 + Onshore Fixed Jack-up Drill Ship Semi-Submersible Tension Leg Tor Bjørnstad 12

13 Troll platform under transport to the field Tor Bjørnstad 13

14 Size comparison of different well-known constructions Eiffel Tower Statfjord C Troll platform Town Hall in Oslo Keops Pyramid Tor Bjørnstad 14

15 World oil production, Tor Bjørnstad 15

16 Industry phases with radiotracer assistance Exploration and appraisal Production operations On-site fluid treatment Fluid transportation Processing Product distribution Environmental monitoring Tor Bjørnstad 16

17 Radiotracers in exploration operations Drilling mud circulation Mud infiltration in near-well and cores Injection profile monitoring Monitoring of cementing level behind casing Monitoring of leakage behind casing Monitoring of perforation efficiency Tor Bjørnstad 17

18 Mud infiltration in near-well and cores Water-based mud is radiolabeled with a water tracer, i.e. HTO which will follow invasion of mud filtrate into the near-well region and into cores extracted for detailed fluid and mineralogic analysis. HTO-concentration in early produced fluids and in fluids extracted from cores defines the level of contamination of these important fluid samples Tor Bjørnstad 18

19 % Formation water in produced water 110 FORMATION WATER FRACTION (%) FORMATION WATER FRACTION (%) TRITIUM IN MUD FRACTION OF FORMATION WATER (%) (Thousands) TIME (min) TIME (min) Tor Bjørnstad 19

20 Oxygen activation method 14 MeV n-generator O O + n 16 n N + p O 16* Oxygen activation N s half-life γ (6.13 MeV) 16 N 16 O + γ Beta Decay Gamma detector O Tor Bjørnstad 20

21 Radiolabelled microsphere method Sucrose is mixed with a 131 Ba salt, powderized and carbonized on the grain surfaces. These particles have specific density close to injection water and gravity segregation is hindered. Carbonization prevents rapid water dissolution. A slurry is injected with injection water and will filter out on the well surface according to the specific zone injectivity Carbon C 131 Ba Sugar Tor Bjørnstad 21

22 Radiolabelled microsphere method Logging with a gamma detector is carried out before tracer injection to establish the baseline. After tracer injection the gamma tool is run again. An activity log as illustrated in the fig. is generated. After some time the microparticles are dissolved and disappear into the formation with the injection water Tor Bjørnstad 22

23 Cementing level A steel casing is normally set in the open hole to stabilize the well. Cement is squeezed between the casing and the formation. Cementing level behind casing is monitored by labelling the first few m 3 with a gamma-emitting tracer. Several tracers can be used but common is 131 I - in the cement water Tor Bjørnstad 23

24 Leakage behind casing Sometimes voids develop behind casing. This may be detrimental to the well performance: Injection fluids take other directions than intended. Produced fluid seems to come from another stratigraphic layer Fluid tracer, typically 131 I -, is injected from a wireline tool and squeezed into formation. An integrated detector monitors upwards movement of tracer behind casing Tor Bjørnstad 24

25 Perforation efficiency Tor Bjørnstad 25

26 Production operations Interwell tracer examinations for flow-field mapping Production mechanisms and EOR-processes Well inflow monitoring (production profiles) Near-well fluid saturations Well stimulation operations Flow assurance operations Multiphase flow monitoring Corrosion, erosion and wear monitoring Tor Bjørnstad 26

27 Tracing of injection fluids (1) Injection well Production well Stratified reservoir Tor Bjørnstad 27

28 Determination of interwell SOR Interwell average SOR may be determinded by simultaneous use of two or more partitioning tracers with different degree of partitioning between fluid phases. The simplest case is the use of both passive and partitioning tracers INTENSITY Passive tracer Water/oil partitioning tracer TIME Distance between equal landmarks on the two profiles is proportional to SOR Tor Bjørnstad 28

29 Common interwell radiotracers As conservative (passive) water tracers: 1. Tritiert vann, HTO, E β = 18 kev, T 1/2 = y Co(CN) 3-6, E γ = 1173 and 1332 kev, T 1/2 = 5.2 y Na +, E γ = 511 and 1274 kev, T 1/2 = 2.5 y 4. S 14 CN -, E β = 159 kev, T 1/2 = 5730 y As oil/water partitioning tracers: 1. n-butanol, 14 C-labelled, E β = 159 kev, T 1/2 = 5730 y 2. IPA, 14 C-labelled, E β = 159 kev, T 1/2 = 5730 y 3. MBK, 14 C-labelled, E β = 159 kev, T 1/2 = 5730 y Tor Bjørnstad 29

30 Observation well operation Intensity Depth Typical tracer: 58 Co(CN) Tor Bjørnstad 30

31 Production profiling velocity shot method Intensity Time Applicable tracer: 131 I - Possible generator: 137 Cs 137m Ba Intensity Time Tor Bjørnstad 31

32 Inflow monitoring in complex wells In-situ tracer generation? Straddle packer Zone 3 Zone 2 Zone 1 Smart proppants Tracer containers Tor Bjørnstad 32

33 Near-well oil saturation water drive (1) Injection: Method based on injection of a slug of radiolabelled ( 14 C og 3 H) ester and push this slug some 5-10 m away from the well. The ester will partition between water and the oil present. Shut-in: Shut in the well for some time (a few days) during which period the ester will hydrolyze to ca 50 % of injected amount: 14 C-Ester + H 2 O Acid + 14 C-Alcohol Backproduction: Remaining ester and reaction products are produced back. The alcohol will operate as a passive water tracer and be produced first. Ester is lagged behind. The difference in arrival time is proportional to the oil saturation Tor Bjørnstad 33

34 Near-well oil saturation water drive (3) Concentration Tracers (ppm) Un-reacted Ester Tracer Product Alcohol Tracer 40 Concentration Tracers (ppm) Volume Produced (bbls) Tor Bjørnstad 34

35 Well stimulation For open-hole completion with sand screen: Radiolabeling of gravel packs. For increased injectivity/-productivity by hydraulic fracturing: Radiolabeling of proppants Tor Bjørnstad 35

36 Hydraulic fracturing real data Before fract. After fract. 124 Sb 46 Sc 192 Ir Tor Bjørnstad 36

37 Multiphase flow monitoring Multiphase flow Homogenization Homogeneous oil/ water dispersion Constant rate injection On-line detection Tracer reservoir Bypass Phase separator Tor Bjørnstad 37

38 Corrosion, erosion and wear Thin-layer activation (TLA): Deuterium irradiation of steel Bulk activation with neutrons: Thermal neutron irradiation of steel d n th Generation of 56 Co and 57 Co Generation of 60 Co and 59 Fe Tor Bjørnstad 38

39 On-site fluid treatment Separator and scrubber efficiency Phase purity (oil-in-water...) Leak detection Natural radioactivity Tor Bjørnstad 39

40 Tracers for separator examinations Typical tracers: 81m Kr or 133 Xe for gas 131 I-iodobenzene for oil 82 Br - for water 1 Time Time Tracer injectjon Measurements Time Tor Bjørnstad 40

41 Liquid carry-over in scrubbers Injection of gas and liquid tracer Wet gas from separator Countrate (cps) Response curve Injeksjon Gassutløp Isokinetic sampling of liquid drops in gas phase i gass fase Time after injection (s) Tor Bjørnstad 41

42 Leaks in heat exchangers Overpressure? Counts per second No leak Seconds after injection 3000 Tracer In Point of measurement Out Counts per second Leak Seconds after injection Tor Bjørnstad 42

43 Transportation (pipelines) Long-range multiphase transportation monitoring Monitoring of liquid hold-up in pipeline gas transportation Monitoring of underground gas storage performance Monitoring of pipeline pigging Tor Bjørnstad 43

44 Long-range multiphase transportation Norwegian North Sea pipeline system for gas, condensate and oil transportation to Scotland, England, France, Belgium and Germany. Radiotracing can be done by for instance: Gas: 133 Xe, 222 Rn Condensate: 3 H-pentane +... Oil: 131 I-iodobenzene +... Radiotracers face strong competition from nonradioactive tracers Tor Bjørnstad 44

45 Liquid hold-up in gas pipelines Injection of water and condensate tracers Detection of tracers Rich gas Examples of tracers: Liquid hold-up 133 Xe for gas HTO for water 3 H-octane and 131 I-iodobenzene for condensate Tor Bjørnstad 45

46 Underground gas storage Often depleted, landbased gas reservoirs. Tracers for gas may be 3 H-labelled light hydrocarbons, but they face strong competition form non-radioactive tracers. Injection well Tor Bjørnstad 46

47 Fluid processing RTD measurements on processing units Efficiency of distillation/- cracking units Integrity of treatment and processing systems Fiscal metering of petroleum products Tor Bjørnstad 47

48 Fiscal metering t x Tracer injectjon Detector 1 Detector 2 The flowrate Q v is found from Q v = x A/ t where A is the cross-sectional area of the pipe Tor Bjørnstad 48

49 Environmental monitoring Monitoring of the biological effects of toxic chemical components in produced waters on neaby sea life (laboratory mechanistic studies with radiolabelled molecules) Monitoring of extent and consentration of NAPLS and DNAPLS in soil for i.e. refineries etc. Specific radiolabelling of oil batches to pinpoint leakages and the sources for spills Labelling of CO 2 in CO 2 sequestration programs Tor Bjørnstad 49

50 Pollution to water Houshold pollution Drill cuttings Cleaning water Produced water Spills Cooling water Cushion water Tor Bjørnstad 50

51 Summary - conclusion Radioactive tracers play a rather important role in petroleum production monitoring programmes In many cases the uniqueness of radiotracers (and other nuclear techniques) makes this technology indispensible for the petroleum industry Some applications are taken over or threatend by the increased use of non-radioactive tracers Worry: Availability of highly skilled and qualified radiotracer personnell. The radiophobia must be met in a constructive way Main message to oilfield end-users: You cannot afford not to use the sharp tools uniqueness offered by radiotracers Tor Bjørnstad 51

52 Tor Bjørnstad 52