Task 2: Matrix Injection Technical Status May2000

1. Task 2: Matrix InjectionTechnical Status May2000 TerraTek, Inc. Heriot -Watt University Triangle Engineering Duke Engineering and Services, Inc. eFirst Technologies Gas Research Institute Advantek, International, Inc VIPS

2. Task 2: Status • ‘Gap Analysis Report’ (May ‘00) • ‘D.P. Format’ (Mar ‘99) on ‘Data CD’ 2.1 Field Data Profiling • ‘(Matrix) Damage Report’ (May ‘00) • ‘Injectivity Models Rep.’ (May ‘00) • ‘Core Test Review’ (Sept. ‘99) 2.2 Public Domain Review Project Subtasks 2.3 Information Management & sorting • Database (TT entering data) • Data List (Rev. 5 issued soon) • Indicated in ‘Gap Report’ (May ‘00) • ‘Data CD’ (May ‘00) • Technical presentations (‘99-’00) 2.4 Analysis 2.5 Protocols • Water Quality Table (Feb. ‘00) • Next focus: Drilling & Completion 2.6 Guidelines for Best Practices • Results from this Workshop?

3. Task 2: Presentation Overview A. Damage Mechanisms during matrix injection • oil and solids near wellbore plugging B. Injectivity Prediction • Summary of models • Field experience • Theoretical modeling C. Analysis Strategy • PWRI JIP and public domain field cases D. Planned Activities

4. (Matrix) Injection Damage Mechanisms (1) • Particle Plugging • Solids and oil in the water (also emulsions?) • Water / Formation Incompatibilities • Fines Migration and Clay Swelling • Hydrocarbon Effects • Wax / asphaltines deposits & relative permeability effects • Scale • Calcium carbonate, calcium sulphate, barium sulphate etc. • Corrosion • Generates iron particles (plugging) • Alters tubing friction - increased tubing roughness (& diameter?)

5. (Matrix) Injection Damage Mechanisms (2) • (lack of) Bacterial Control • Biomass and / or “Schmoo” • Described by Fambrough et al. (SPE 28976), McLelland and others • Main components of “Schmoo”: • Sand and formation fines in the PW • Hydrocarbon material in the PW (OIW) • Iron sulphide, from the injection system • Production chemicals • Biomass-material • “Schmoo” prediction requires extensive water quality / surface facility information

6. Bacterial count (CFU/g) TSS: particle count (ppm) and size distribution (mm) OIW: Particle count (ppm) and droplet size (mm) Critical injection velocity (m/s) Dissolved gases (CO2, O2, H2S etc.) TDS (ppm) AW / PW compatibility Temperature Analysis of produced and formation water characteristics Formation damage mechanisms Scale inhibitor injection at surface Bacterial growth, plugging Corrosion due to SRB • Formation / pore plugging • creating filter cakes • Solid particles • Oil droplets • Oily solid particles • Emulsions, wax, oil bank • (affecting relative perm.) • Other hydrocarbon deposits • (schmoo) etc. Acid stimulation Fracture (increase wellbore) Filtration Solvents and/or surfactants injection Separation, solvents, surfactants Biocides Scale precipitation: CaCO3, CaSO4, BaSO4 etc. Corrosion (tubing, surface equipment damages, causing iron solids plugging) Fines migration Acid stimulation Biocides Tubing wash or matrix stimulation Fluid depends on scale type Acid stimulation Fracturing Corrosion inhibitors (Scavengers) Material selection Adjust flow rate (bpd), Increase pay zone periodic stabling treatments Control Remedial action Damage - Mitigation - Stimulation “Roadmap” Subject of Task 4 - Damage and Stimulation

7. Damage of Matrix versus Fractured Wells Matrix Injection Fractured Well DIFFERENCES • surface area • leak-off (cross-flow or static filtration) • plugging mechanisms

8. Near-Wellbore Plugging • Damage mechanisms: • Plugging by Solids in Water (TSS) • Plugging by Oil in Water (OIW) • Plugging by Solids in the presence of oil (TFS) • Other effects: • Fines migration • Clay swelling • Bacterial activity (in surface facilities/near wellbore area) • Drilling and completion practices • Other factors?

9. Solids Plugging - Abram’s “rule of thumb” • Solids invasion • “Internal Filter Cake” formed when: 1/3 pore throat < particle size > 1/7 pore throat • “External Filter Cake” • Particles > one third pore throat diameter • Only applies to concentrated solid suspensions • Pore throat diameter often has to be estimated from permeability (Kozeny / Carmen etc.)

10. Internal accumulation External accumulation Large Solids Small Solids Solids Plugging - Simple models separate “External” & “Internal” Processes • Also Wellbore Narrowing & Perforation Plugging

11. Solids Plugging - more complex models • Solids invasion: “Internal Filter Cake” • “External Filter Cake” Particles start to deposit on grains Pore throats get narrower and trap further particles More and more pores plugged, particles accumulate towards the wellbore a) Particles larger than pore diameter are filtered out at the wellbore b) No further solids invasion once internal filter cake has reached the wellbore

12. Near-Wellbore Plugging • Damage mechanisms: • Plugging by Solids in Water (TSS) • Plugging by Oil in Water (OIW) • Plugging by Solids in the presence of oil (TFS) • Other effects: • Fines migration • Clay swelling • Bacterial activity (in surface facilities/near wellbore area) • Drilling and completion practices • Other factors?

13. Oil droplet larger than pore throat - deformable with enough pressure drop Impact of Oil in the Water • a) Plugging of Oil droplets • Emulsions (increased viscosity) • Relative Permeability effects • b) Enhanced plugging of solids in the presence of oil

14. Solids prevent oil droplet deforming / oil sticks several solid particles together; enlarging radius Impact of Oil in the Water • a) Plugging of Oil droplets • Emulsions • Relative Permeability effects • b) Enhanced plugging of solids in the presence of oil

15. High perm zone Producer Injector High perm zone PWRI into Layered Formations (Matrix) • Differential plugging may have -ve or +ve effect - depends on relative rates in high / low perm zones • Injection of “clean water”: Early water breakthrough • Plugging of high perm zone promotes piston-like displacement & improved sweep efficiency

16. Near-Wellbore Plugging • Damage mechanisms: • Plugging by Solids in Water (TSS) • Plugging by Oil in Water (OIW) • Plugging by Solids in the presence of oil (TFS) • Other effects: • Fines migration • Clay swelling • Bacterial activity (in surface facilities/near wellbore area) • Drilling and completion practices • Other factors?

17. Published models (Most assume matrix flow) In-house company models Semi “Commercial” programs “Commercial” programs available through software house Shell models (B&D) Texas Univ. models Heriot-Watt models IFP models Etc. Van Velzen Model (Shell) WID (Texas Univ.) None known (Matrix) Injectivity Prediction Models

18. (Matrix) Injectivity Prediction Models (1) • Models identified and briefly described • Brief summary of required input parameters for “selected models” (some may be missing) • Less emphasis on numerical models

19. (Matrix) Injectivity Prediction Models (2)

20. (Matrix) Injectivity Prediction Models (3)

21. (Matrix) Injectivity Prediction Models (4) Pang and Sharma developed equations for filtration parameters when core tests were not available

22. (Matrix) Injectivity Prediction Models (5) • All models require information from core tests • How relevant for downhole PWRI conditions? • None of these account for Oil-in-Water • Limited field validation reported Some parameters readily available, others more difficult to determine / estimate

23. Validation of WID (University of Texas, Austin) • Reported by Sharma et al. in paper SPE 38180 and in Wennberg’s PhD thesis (1998): The match is sometimes good • Gulf of Mexico - “Soft Sand”. • Wells gravel packed (12/20 mesh) with wire-wrapped screens (12 gauge). • “Clean” sea water (TSS < 10 ppm, average particle diameter 2-3 mm).

24. Validation of WID (University of Texas, Austin) • … but in some wells under estimated

25. Validation of WID (University of Texas, Austin) • … and in some wells over-estimated In this case - The damage is a combination of formation damage and completion damage (plugging of gravel packs) - We need to differentiate -

26. A model that includes oil • Zara Khatib: ‘FORDAM’ Model • A numerical model for damage in different types of wells (SPE 28488) • ‘Open hole’, ‘Cased & perforated’, ‘Perforated & Gravel Packed’ and ‘(Static) hydraulic fractured’ • “Static filtration” • Effects of suspended OIW in the injection stream: Up to 50% additional decrease in permeability

27. ‘FORDAM’ • Effects of solids composition and compressibility • Investigation into the relationship between the types of solids and compressibility of the filter cake • Corrosion, scale, biomass and production chemicals are all compressible materials • Filter cake porosity is not constant and varies with injection pressure (and rate) - affecting permeability Downhole samples indicate that often iron particles are of much higher concentration than formation fines - Cliffort et al, 1991

28. How Valid are the Models in PWRI Situations? • In general, reports on ‘relevant’ field validation of the models are limited • Based on Matrix Conditions (static filtration) • Often used to predict matrix injection behaviour in a well with a propagating fracture - hence under prediction • are limited to plugging by solids - not other potential damage mechanisms • Matrix injection usually decreases to plateau but continues for a long time • Where do the solids go?

29. Matrix Injection Field data • Where do solids go once external cake formed / perforation tunnels filled? • Cavities?

30. (Matrix) Injectivity Prediction Models • Do we need matrix injectivity decline models? • Yes (also for layered formations / stimulation tasks) • Available models insufficient / too complicated? • What kind of models do the sponsors need? • A simple PEA-23 - type correlation • Total suspended solids (threshold concentration) • Oil-in-water • Water temperature • Permeability • Time (or cumulative solids injected) • Particle diameter (constant)??? II (TSS, OIW, T, k, t)

31. Commercial Simulators* Highest R. E**. (%) Validated Models SP5, SP1, SP4, SP2 Multi-Phase Flow Models 7.7 SP5, SP1, SP4, SP2 Temperature profile 6.0 Choke SP5, SP1, SP4, SP2 8.5 1.0 SP5, SP1, SP4 Gas Lift 2.0 ESP SP5, SP1, SP4 SP1, SP4 Separator 0.8 SP5, SP1, SP4 Compression 5.5 SP5, SP1, SP4, SP2 PVT properties 5.0 Commingled Flow SP5, SP1, SP4 Same or 0% Analysis Strategy (1) • Develop agreed spread sheet so that all analyses on same basis (see CD) • Importance: * Software package **Relative error in flow rate

32. Analysis Strategy (2) • Review data made available to PWRI project • Developed (some) familiarity with contents • Data profiling to help identify where it is most relevant • (Very) Basic quality control checks • Two types of analysis possible: • statistical analysis on large data sets • specific example well analysis

33. (Potential) Matrix Injection Field Cases • Field Examples (Project and Public Domain) • Consolidated Sandstone: NAM-1 (Disposal well), PCP DHOWS case (public domain, disposal), Norsk Hydro (Brage re-injection, semi consolidated?), Canadian Petroleum in Yemen (public domain disposal), Shell Nigeria (disposal), PCP Countess? (hydraulic fractured wells, fracture pressure not known) Eider (closed fracture), “C” (PEA-23 case PWRI). • Unconsolidated sandstone - Heidrun (SWI), H01 (AWI+PWRI), Elf-3 (PWRI), Shell GOM (SWI, public domain) • Carbonate formations (chalk, limestone) - Mærsk (A and C), Ghawar (limestone, SWI) • Many seawater injection and / or disposal wells • rather than PWRI

34. Analysis Strategy (2) • Review data made available to PWRI project • Developed familiarity with contents • Data profiling to help identify where it is most relevant • (Very) Basic quality control checks • Two types of analysis possible: • statistical analysis on large data sets • specific example well analysis

35. One type of data required Impact of Water Quality on Injectivity of Well From Field C, PEA 23 (fractured well)

36. One type of data required Impact of Water Quality on Injectivity of Well From Field ‘C’, PEA-23 (fractured well)

37. Analysis Strategy (3) • Typical Example Wells for further study • Consolidated Sandstone • Unconsolidated sandstone • Carbonate formations (chalk, limestone) • Need to identify with sponsors: • data sets for “hi-grading” • confirm analysis resultswith sponsors

38. Field Example: Ghawar Field, Saudi Arabia • McCune related Injectivity decline rate to (very clean) sea water quality (From SPE 25531 (Bayona, 1993) and Report recently provided by Chevron)

39. Field Example: Ghawar Field, Saudi Arabia • Average for 92 wells - but TSS may be measured 150 km from wells

40. II (bpd/psi) OIW (ppm) Field Example: Maersk Field ‘A’

41. Field Example: Maersk Field ‘A’ • No relationship between injectivity & OIW identified so far

42. Analysis Strategy (3) • Typical Example Wells for further study • Consolidated Sandstone • Unconsolidated sandstone • Carbonate formations (chalk, limestone) • Need to identify with sponsors: • Data sets for “hi-grading” • Confirm analysis resultswith sponsors before reporting

43. Analysis Strategy (4) • Alternative approach: • Generation of best practices by linking donated data, reports etc.

44. Corrosion Iron solids plugging Inorganic scaling PWRI Damage Mechanisms Relative permeability changes Organic scaling Bacteria growth, plugging, “schmoo” Fines migration • Formation pore plugging • Solid particles • Oil droplets • Oily solid particles Fractures plugged withsolids from injection fluid Damaged zone (mud filtrate, completion/injection fluids, etc) Mud filtercake

45. Analysis Strategy (4) • Alternative approach: • generation of best practices by linking donated data, reports etc. • Not sure practical for Matrix due to limited occurrence in project data

46. Task 2: Status • ‘Gap Analysis Report’ (May ‘00) • ‘D.P. Format’ (Mar ‘99) on ‘Data CD’ 2.1 Field Data Profiling • ‘(Matrix) Damage Report’ (May ‘00) • ‘Injectivity Models Rep.’ (May ‘00) • ‘Core Test Review’ (Sept. ‘99) 2.2 Public Domain Review Project Subtasks 2.3 Information Management & sorting • Database (TT entering data) • Data List (Rev. 5 issued soon) • Indicated in ‘Gap Report’ (May ‘00) • ‘Data CD’ (May ‘00) • Technical presentations (‘99-’00) • Analysis of Example Wells 2.4 Analysis 2.5 Protocols • Water Quality Table (Feb. ‘00) • Next focus: Drilling & Completion 2.6 Guidelines for Best Practices • Results from this Workshop?

47. Proposed Activities next six months • Finalise draft reports • ‘Target Wells’ • ‘Hard’ Sandstone priority (NAM-1, … others?) • Soft sandstone (Elf-3, BP-H01………….others?) • Carbonate (selected Maersk wells ……….others?) • visit / contact operator donating data • Drilling / Completion Techniques & Best Practises • From this workshop • Stimulation of Matrix Wells • From Task 4

48. (Matrix) Injectivity Prediction Models • Do we need matrix injectivity decline models? • Yes (also for layered formations / stimulation tasks) • Available models insufficient / too complicated? • What kind of models do the sponsors need? • A simple PEA-23 - type correlation • Total suspended solids (threshold concentration) • Oil-in-water • Water temperature • Permeability • Time (or cumulative solids injected) • Particle diameter (constant)??? II (TSS, OIW, T, k, t)