Recent Advances in Oil and Gas Production Engineering

1. Recent Advances in Oil and Gas Production Engineering Professor Ma Xianlin School of Petroleum Engineering Xi’an Shiyou University

2. Course Contents: Chapter 1 Introduction Chapter 2 Gas Well Unloading Technologies Chapter 3 Advanced Hydraulic Fracturing Technologies Chapter 4 Horizontal Well Fracturing Chapter 5 Coiled Tubing Operations and Intelligent Well Chapter 6 Unconventional Oil and Gas Production Chapter 7 Shale Gas Development

3. Chapter 3Advanced Hydraulic Fracturing Technologies Outline 3.1 Review of hydraulic fracturing 3.2 Multi-layer fracturing 3.3 Tip screen out technology 3.4 Fracture height control 3.5 Forced closure technology 3.6 Refracturing 3.7 Unified Fracture Design

4. What is Hydraulic Fracturing (Fracing)? • Fracturing fluid is pump at high pressure into formation to create fractures that connect reservoir and wellbore • First used in U.S. in 1947

5. Why Hydraulic Fracture ? • Hydraulic fracture operations may be performed on a well for one (or more) of three reasons: • to extend a conductive path deep into a formation and thus increase productivity beyond the natural level • to alter fluid flow in the formation. • to bypass near-wellbore damage (by drilling) and return a well to its “natural” permeability

6. Role of Hydraulic Fracture-1 • Intermediate, high permeability reservoir • Accelerated rate • Produce hydrocarbons quicker • Increase the present value of hydrocarbons

7. Role of Hydraulic Fracture -2 • Low permeability reservoir • Additional recovery • Ultimately produce more hydrocarbons • Increase area drained by a single well

8. Change flow pattern Radial flow disappears, wellbore radius is not a factor any more

9. Fracture Orientation Fracture orientation is perpendicular to the direction of the least in-situ principal stress.

10. Fracture Geometries -1 Horizontal Well Horizontal Well Vertical Well Vertical Fracture Transverse Vertical Fracture SRV: Stimulated Reservoir Volume Longitudinal Vertical Fracture

11. Fracture Geometries -2

12. Hydraulic Fracturing Process • Pressure the reservoir rock using a fluid to create a fracture • Grow fracture by continuing to pump fluids into the fractures • Pump proppant materials into fracture in form of a slurry, as part of the fracture fluid • Stop pumping and flowback to the well to recover the fracture fluids while leaving the proppant in place in reservoir

13. World’s largest Frac Job in Canada by Apache Modern Frac Fleet on location

14. World’s largest Frac Job in Canada by Apache -2

15. World’s largest Frac Job in Canada by Apache -3 Fresh water usage: total of about 890,303m3 Each frac averaged 3,249m3 of water Removed 15 centimeters from the lake level, recovered 5 centimeters

16. Hydraulic Fracturing Water Cycle • Water is withdrawn from ground water and surface water • Water is combined with chemical additives and proppant to make the hydraulic fracturing fluid. • Pressurized hydraulic fracturing fluid is injected into the well • Fracturing fluid flows back up to well

17. Properties of a fracture fluid • Viscosity • Controls fracture width (near wellbore) • Impacts proppant transport • Fluid loss • Controls amount of fluid in fracture • Impacts fracture geometry • Density • Controls hydrostatic gradients • Impacts proppant convection • Friction • Controls surface treating pressure • Impacts injection rate • pH • Controls crosslinker reactions • Impacts fluid properties

18. Fluid efficiency • Definition: percentage of fluid in the fracture • Affects created fracture dimensions • High leakoff can lead to screenouts • Low leakoff affects proppant placement • Convection • Settling

19. Effect of Fluid Efficiency • Low fluid efficiency Short fracture, High filtration • High fluid efficiency Longer fracture, Low filtration

20. Fracture Fluid Composition Volumetric composition of a fracturing fluid Water and sand 99.51% Additives

21. Fracturing fluids and conditions for their use

22. Additives -1 • Gelling Agents • Viscosifiersused to thicken fracturing fluids (1’s to 10’s of centipoise) to improve proppant transport. • Guar or modified Guar Gum • Crosslinkers • used to super-thicken fracturing fluids (100’s to 1000’s of centipoise) • Energizing Gases • Used to aid fracturing fluid recovery • CO2 or N2 or both

23. Additives -2 • Clay Control Agents • Prevent clay swelling and minimize migration of clay fines • Biocides • Kill bacteria in fracturing fluid make-up waters • Used to minimize souring of reservoirs resulting from injection of contaminated surface water • Used to prevent bacteria in make-up water from destroying gelling agents before the treatment can be pumped • Gelling Agent = Bug Food

24. Additive -3 • Friction Reducers • Used in Slickwater Fracs to reduce friction losses in pipe while injecting fracturing fluids • Breakers • Used to reduce viscosity of fracturing fluids after treatment to allow fluids to more easily flow out of the formation for recovery • Surfactants • Surfactants reduce surface tension – aid in fluid recovery

25. Water-Based Fracturing fluid systems • Polymer systems • Crosslinked • High or low pH • Instant or delayed crosslink • Linear systems • High gel loading • Slickwater • Non-polymer systems • Viscoelastic surfactant

26. Linear Gel fluids • Polymers

27. Cross-linking Agents • Crosslinker • Borate • Titanium • Zirconium • Antimony • Aluminum

28. Crosslink Mechanisms • Linear gels have inadequate viscosity to transport proppant deep into fracture • Metal crosslinkers added to linear gel fluids, which link linear gel polymer chains together, creating extremely long polymer chains • As polymer chain length increases, viscosity of fluid increases • Crosslinking can be controlled by temperature and pH

29. Timing of Crosslink reaction • Rapid crosslink increases friction pressure • Rapid crosslink followed by shearing down tubulars reduces final viscosity • The crosslink reaction can be accelerated or delayed on most fracture fluid systems • Some systems are temperature activated • Some systems are controlled by chemical concentrations (Buffers)

30. Foamed Fracturing Fluids • Two phases • More complex than single-phase fluid • Reduces leakoff • Reduces solids • Viscosity depends on • Foam Quality (liquid/gas interaction) • Foam texture (bubbles size distribution) • Rheological properties of base fluid • Temperature and pressure • Shear history

31. Slickwater Frac (Water frac, Riverfrac) • Use of less viscous slickwater fluids pumped at high rates (> 60bpm) to generate narrowfractures with lowconcentrationsbutlarge volume of proppant • Slickened to reduce friction in tubing/casing • Friction reducer and/or Linear Gel • These are NOT proppantless waterfracs • Standard technique in fracture stimulation of several U.S. shales • Hybrids • Typically use a combination of cross-linked stages and slickwater

32. Slickwater Frac Advantages & Disadvantages • Advantages • High retained conductivity, due to no filtercake present • Typically result in highly complex fractures • Typically less expensive (reduced number of fluid additives) • Disposal and/or reuse of produced/load water • Disadvantages • Larger volumes of water • Larger horsepower requirement (to keep high pump rates, 60-110bpm). • Limited fracture-width (due to low maximum concentration proppant in low viscosity). • Reduced %-flowback-water recovery (imbibitions of fracturing fluid in complex fracture network). • Limitation to fine-mesh propping agents(reduced ability of nonviscous fluids in transport of large proppants)

33. Keeping fracture open: Proppants Open fracture during job (frac width = wf) • Keep the fracture propped open throughout the created fracture area • Across the length and height of the interval • Provide sufficient conductivity contrast to accelerate flow to the wellbore • Provide permeable pathway • Maintain fracture width Fracture tends to close once the pressure has been released Proppants used to keep fracopen

34. Types of Proppant

35. Proppant Conductivity

36. Proppant Types and their conductivity

37. Proppant selection considerations -1 • Proppant permeability is a key design parameter dependent on • Size distribution (larger size provides higher perm) • Closure stress • Damage • Proppant permeability can change over the life of the well • Production damage (scale, fines, etc.) • Settling • Rate of settling increases proportional to (diameter)2

38. Embedment Damage • Proppant embedment ranges from minimal in hard formations to typically as much as ½ grain diameter in soft formations • Damage from embedment is two-fold: width loss and fines

39. Fracturing Materials • Fracturing materials are essential tools in a toolbox • Each material has its application range • Applying fracturing materials outside of their application ranges is likely to lead to catastrophe • No material is universal, i.e. no one fracturing material is appropriate for every reservoir

40. Tracking Fracturing in Real Time • Microseismics are used, as well as tilt measurement (more on this later)

41. Fracture orientation changes

42. Fractures rise out of zone

43. Fracture Growth is more complex than we tend to think

44. Ideal Fracture vs. “Real” Fracture

45. Post fracture treatment monitoring methods • Conventional temperature and tracer surveys • Immediate or near-immediate post-frac • Data pertains only to immediate wellbore vicinity • Requires post-treatment logging • Fluids and proppant can be traced • Distributed temperature sensing (DST) • Especially useful for cleanup studies • Production logging • Spinner surveys • Requires logging well after fracture fluid cleanup • Microseismic monitoring • During the fracture treatment • Near real-time • May be used for post-treatment analysis and for near real-time treatment management

46. Monitoring Hydraulic Fracturing • Precision real-time tilt monitoring • Microseismic monitoring using geophonses at depth relatively near the fracture site • Pressure-time response in the injection well • Borehole geophysical logging

47. Monitoring Formation Response Assessment of formation response = improved design and process control

48. Tiltmeter Fracture Mapping • Downhole tiltmeters • Tilts measured • Mathematical solution

49. Microseismic Monitoring Concept

50. Microseismic Monitoring • Promising surveillance technology for all process involving reservoir-scale changes in volume. • Tracks regions of elevated shear stress, high pressure causing slip. • Surveillance for shale gas fracturing has proven to be a seminal application. • MS data help to delineate the stimulated volume which is far larger than the volume that sand has reached