Geothermal Well Drilling – Keep it Simple
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The cost of drilling geothermal wells has increased dramatically over the past 10 years, with drilling now making up a larger portion of total project costs. Many factors influence increased drilling expenses, including influences from the oil and gas industry, rising contractor and materials costs, and bureaucratic processes. However, some costs that can be controlled with simplification include procurement, wellhead location, well design, casing specification, drilling equipment, cementing, mud engineering, and completion testing. By keeping designs, processes, and operations as simple as possible, geothermal project viability may be improved.
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Geothermal Well Drilling – Keep it Simple
- 1. Hagen Hole Geothermal Consultants New Zealand Limited ICELAND GEOTHERMAL CONFERENCE - March 5 – 8, 2013
- 2. Geothermal Consultants New Zealand Limited The cost of drilling geothermal wells has risen dramatically over the past 10 years – in general: - • Rate of cost increase is out of proportion with inflation • Rate of cost increase is out of proportion with that seen in plant and gathering system construction costs • Drilling now a bigger part of the total project cost pie
- 3. WELL DRILLING COST “RISING” Geothermal Consultants New Zealand Limited $- $2,00 $4,00 $6,00 $8,00 $10,00 $12,00 $14,00 1970 1980 1990 2000 2010 2020 WellCostUS$Million) Geothermal Well Drilling Cost
- 4. The Viability of Many Geothermal Projects is Under Significant Threat!!! Geothermal Consultants New Zealand Limited
- 5. Geothermal Consultants New Zealand Limited What’s Driving These Costs Upwards ? • O & G Industry influence - Inflation • Increased contractor costs • Drilling Services Contractors (Rig Suppliers) • Secondary Service Contractors - Cementing Services; Mud Engineering; Directional Drilling; etc. • Increased Materials’ costs • Steel Tubulars and Accessories • Oilwell cement and additives • Drilling Mud and additives There is little we can do to control these!
- 6. Geothermal Consultants New Zealand Limited Factors That Can Increase Drilling Costs That We Can Control • Bureaucracy and Management • Procurement • Wellhead and Drilling Pad Location and Preparation • Well Design • Casing Specification • Drill Bit and Bottom Hole Assembly Components • Cementing • Mud Engineering • Directional Drilling • Completion Testing
- 7. Geothermal Consultants New Zealand Limited Bureaucracy and Management Typically large organisations drill more expensive wells than small organisations • More Bureaucratic processes • More people to do same job • Management Structure usually Vertical • Time lost in Decision Making • Decisions often made by unqualified personnel • Important to push Drilling Decision Making down to the people who “KNOW BEST” - the people on site running and managing the Rig KEEP THE MANAGEMENT STRUCTURE SIMPLE
- 8. Geothermal Consultants New Zealand Limited Procurement Procurement processes are often controlled by intricate and overbearing Corporate, Government, and/or Funding Agency policies:- • Significant “Time Loss” to process purchase specifications • Long response times result in downtime • Restrictive procurement results in less than optimum materials and equipment Procurement Processes Need to be OPTIMISED and SIMPLIFIED
- 9. Geothermal Consultants New Zealand Limited Wellhead and Drilling Pad Location and Preparation Choose wellhead location / Drilling pad location such that civil preparation is minimised. Don’t be dazzled by requirements for “exact” location. Prior to commencing any civil site preparation works, drill a small diameter (±30mm) test well at chosen location to check:- • Near surface geotechnical conditions • Need for site grouting • Required conductor depth • Required surface casing depth SIMPLIFY the process
- 10. Geothermal Consultants New Zealand Limited Well Design Minimise or Eliminate Risk :- • Nested liners • Tied back casings • Staged cement collars • Hangers KEEP THE DESIGN SIMPLE Slotted Liner Production Casing 750 - 1500 m Anchor Casing 250 - 500 m Intermediate Casing 150 - 250 m (Not always necessary) Surface Casing 40 - 100 m Conductor 10 - 40 m Connection to permanent wellhead assembly All casings fully cement back to surface NOTE: An intermediate casing may be installed between the anchor and production casing. 1250 - 3000 m NOT TO SCALE
- 11. Geothermal Consultants New Zealand Limited Casing Specification There has been a tendency to move from ‘Standard Buttress’ connection casing to ‘Premium’ connection casing • Significantly more expensive (as much as 3 to 4 times) • Often more difficult and slower to run Arguments for Premium Connection – Gas tight, higher Compressive strength - We don’t really need gas tight connections - Buttress ~15% better Compressive Strength if fully constrained Keep Casing Specification SIMPLE
- 12. Geothermal Consultants New Zealand Limited Drill Bit and Bottom Hole Assembly Components Procurement processes need to be adapted to allow purchase of the Highest Quality not the least price – tripping time more costly!! Look at utilizing PDC Bits Simplify BHA design!! Minimise use of mud motors Use simple rotary assemblies
- 13. Geothermal Consultants New Zealand Limited Cementing • Avoid complicated processes – stage cementing, tie backs • Simplest approach – long string casings back to surface – but requires careful management • Avoid “special” materials – light materials, foamed cement • Be aware of the ‘carbonation of silica’ in CO2 rich fluids Keep Cementing SIMPLE
- 14. Mud Engineering Geothermal Consultants New Zealand Limited In the vast majority of geothermal fields it is not necessary to use ‘specialised’ drilling muds. Initially a very simple non-dispersed, water based ‘spud’ mud Then simple water based lightly dispersed mud with polymer viscosifiers When circulation is lost – drill with water ‘blind’ or preferably aerated water with polymer sweeps But SIMPLE
- 15. Directional Drilling Geothermal Consultants New Zealand Limited 0,0 200,0 400,0 600,0 800,0 1000,0 1200,0 1400,0 1600,0 1800,0 2000,0 2200,0 2400,0 -100 0 100 200 300 400 500 600 700 800 9001000 VerticalDepth(m) Metres from wellhead Kawerau WELLKA-53 SECTION on 250° Azimuthal Plane Welltrack must be simple – J type Design for build-up section to be as shallow as possible Minimise use of Mud Motor and MWD – over correction – torque & drag Keep welltrack and build up section SIMPLE
- 16. Geothermal Consultants New Zealand Limited Completion Testing There is a tendency to over test – carry out just what is needed Perform ‘open hole’ logging only if absolutely necessary, and only if the open hole is absolutely stable - Minimise the risk Run Liner – then carry out ‘standard’ completion tests Injectivity, and PTS Logs
- 17. Conclusion KEEP IT SIMPLE Geothermal Consultants New Zealand Limited
- 18. Geothermal Consultants New Zealand Limited Thank you