An Introduction to Drilling for Coal Geologists

Transcription

1 An Introduction to Drilling for Coal Geologists Terminology Drill Rod/Pipe individual length of pipe (rod), can be 3m, 6m or maybe longer in cases. Drill String assembled collection of the drill pipe, and bits. 100 rods x 3m length = 300m drill string Top Head Drive Rig - rotation and circulation is driven from the top of the drill string, moves in a track along the derrick/tower Rotary Table Drive Rig rotation is achieved by turning a square or hexagonal pipe (the "Kelly") at drill floor level 2 1

2 Why do we drill holes? EXPLORATION Green and Brown fields exploration Resource evaluation Geophysical surveys (Seismic) GEOTECHNICAL INVESTIGATIONS Gather information for rock & soil strengths ENVIRONMENTAL INVESTIGATIONS Environmental Impact Statements (EIS) WATER BORES MINE DESIGN, CONSTRUCTION, & PRODUCTION Shaft Development, gas drainage, etc 3 What do we achieve? Presence of a resource? Depth and thickness for modelling Help define geological features that will affect mining (intrusions, faults, aquifer, gas) Lithological sequence for correlation Samples for coal quality analysis to derive product coal specifications Geotechnical information to plan and different mining methods and safety requirements Geochemical information for waste management (acidic breakdown, trace elements) 4 2

3 Drill Site Setup 5 ROTARY/REVERSE CIRCULATION (RC) RIGS Basic lithological data no decent uncontaminated sample for coal testing Often used for LOX drilling Pilot holes, seismic holes, blast holes, etc Relatively rapid can gain geologic information quickly Often a cheaper form of drilling compared to coring Detail of lithological information is limited Hammer drilling for harder rocks e.g. basalts and intrusions 6 3

4 Chip Drilling Gives Rock Chips Chip Samples 7 ROTARY/REVERSE CIRCULATION OR CHIP DRILLING Blade for softer near surface sediments PCD (polycrystalline compact diamond) PCD bits are ideal for drilling in soft to medium homogeneous and competent sedimentary formations. 8 4

5 TYPICAL ROTARY AND RC RIGS Rotary/Multipurpose Rig Reverse Circulation (RC) Rig 9 CORE DRILLING Solid representation of strata Gathers detailed lithological data - coal quality, geotechnical, geochemical information 10 5

6 CORE SIZES Core size is the diameter of the physical core, not the hole size 11 HOLE SIZES Relates to the size of the hole created by the drill bit 12 6

7 Two methods wireline & conventional Conventional Core - retrieved by removing every rod Wireline Drilling core retrieved by wireline overshot system within rods Fact: Boart Longyear developed the wireline system 13 Required for resource classification Inferred, indicated, measured (JORC) Target a range of depths size can dictate Have limitations, slower production, expensive De-risk your project Increase value of your asset Coal quality testing Whole other slide show! 14 7

8 What does a Geologist do at a Drill Rig? To safely collect clean, quality data Cross check progress with driller conditions in the hole, depths, target depths and hole designs Provide written, photographic, and geophysically corrected log of the formations uncovered Take samples as appropriate and store core as required Sign-off drillers paperwork each day Look for the unexpected Know your driller you have to work as a team! 15 Gamma and Density Log Responses To The BHWL 16 8

9 Some things to watch for Is there Existing Data? How Detailed / Reliable? Can it be used to make informed drill hole predictions? Unexpected changes in Formations Could imply faulting or change of sedimentary environment Core Loss and Expanded Core Needs to be understood as part of drilling process to be accurately dealt with Coked Coal can take on a range of appearances or disappear completely Bore Hole Lifecycle 17 Questions 18 9