CHAPTER 9 DRILLING EQUIPMENT, OPERATIONS AND LIMITATIONS
| Jurisdiction | United States |
(Apr 1980)
DRILLING EQUIPMENT, OPERATIONS AND LIMITATIONS
AMAX Exploration, Inc.
Denver, Colorado
TABLE OF CONTENTS
Introduction
1. Planning
2. Location and Logistics
3. Lithology and Structures
4. Size of Program
5. Equipment
A. Diamond Drilling
B. Rotary Drilling
C. Rotary Percussive Drilling
D. Hammer Drills
E. Reverse Circulation
F. Air Compressors
G. Sampling Equipment
6. Climatic Conditions
7. Water Supply and Circulation
8. Manpower
9. Problems in Drilling
A. Deviation in Diamond Drill Holes
B. Cementing
C. Diamond Bit Costs
D. Drill Mud
10. Drilling Costs
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Introduction
On exploration projects where drilling is required, that drilling cost may represent from 20 to 60 percent of the entire project's budget; however, by the time a mineralized zone is transformed into an economic ore deposit (that is a producing mine), the drill costs will vary from 1-1/2 percent to 6 percent of the total costs of that project.
Drilling is a requirement when property payments are due in short order or decisions required in operating. Mining companies categorize drilling as follows:
1. Exploration — or wildcat drilling
2. Mine evaluation — close spacing to check continuity and large diameter cores for metallurgical studies.
3. Mine operating which includes:
a. Mineable possible reserves — drilling on a wide grid pattern.
b. Mineable proven reserves — drilling on close centers for mine planning.
c. Mine grade control — to check grades of minerals being fed into a mill.
Up until a few years ago, diamond core drilling was the only accepted method of drilling. Today diamond core drilling amounts to between 30 to 35 percent of our exploration drilling with the remainder being drilled by various types of rotary or rotary percussive machines.
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The success of a project depends largely upon the amount of investigation and research spent on the area to be drilled. Those of us who have the obligation to obtain the maximum amount of usable geologic information from a drill hole at a minimum cost are going to evaluate the following conditions:
1. Planning
2. Location and Logistics
3. Lithology and Structures
4. Size of Program
5. Equipment
6. Climatic Conditions
7. Water Supplies
8. Manpower
9. Problems in Drilling
10. Drilling Costs
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1. Planning
What are the objectives of the project, and how much money is available? What method of sampling can we use which will give us the maximum amount of information at a minimal cost?
2. Location and Logistics
The location and logistics for running a drill project may sometimes cost as much as the direct drilling cost which are generated on that project. Air support projects, either with fixed wings and/or helicopters, and water supported projects using boats or barges, need to be watched closely. I have seen projects in the mountains where bulldozer costs for maintaining roads are more than the drilling costs. Because of restrictions caused by either government or the environment on making roads, many drills personnel carriers and water tanks are being mounted on tracked vehicles,
3. Lithology and Structures
The types of formations and structures to be penetrated are the controlling factors as to what size hole should be drilled in order to achieve the objectives of the program. Overburden can be troublesome, depending on its thickness and whether it is derived from glacial till, river gravels, blow sand, talus, erosion of rock formations, or other means. These factors will influence the kind of equipment selected and methods of penetration. After casing into bedrock, if it is required, various problems can arise which may keep the bit from hitting the target. Such problems are: rock strengths of a given formation especially in large diameter coring — these pressures may exceed 70,000 psi, permafrost, bedding planes of formations, schistosity and/or gneissosity, or interbedded soft and hard layers which can all contribute to deviation problems. If deviation problems are suspected prior to drilling, larger size holes should be considered as well as special bit designs and controlled weights on the bit. Suspected fault zones may create problems such as fluid entry or loss, gouge material which could spill into the hold and numerous other problems. If it is known that problems may exist at depth, a larger size hole should be drilled to allow for a reduction at depth to overcome the problems. The larger size will be a comparatively small amount to the alternatives of reaming or wedging or even losing the hole completely.
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4. Size of Program
The size of the job will determine the amount of equipment required to complete the work within a given...
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