Boring or penetrating the earth – Automatic control
Patent
1992-09-04
1994-06-07
Bui, Thuy M.
Boring or penetrating the earth
Automatic control
E21B 4400
Patent
active
053181360
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with improvements in or relating to drilling processes and drilling apparatus and is especially concerned with optimisation of rotary drilling parameters, for example in drilling through rock strata when drilling for minerals, gas or oil.
Drilling activities in the mining and oil industries are highly susceptible to the economic fortunes of those industries.
During periods of strong product prices the drilling market is buoyant, however depressed prices result in fierce competition and cost cutting amongst both contractors and supply companies. The continuing pressure on prices is causing increased interest in the efficiency of drilling operations and the optimisation of drilling performances. Improvements have been progressively made in increasing in drilling efficiency and advances in computer technology have enabled development of automated drilling rigs which include both functional control and data logging facilities.
However, obtaining optimum performance in drilling operations still remains highly dependent on the skill, expertise and experience of the personnel involved.
Optimum performance can be judged by considering any one or a combination of factors including drilling rate, total time to hole completion, percentage core recovery, bit lift, etc. In the current highly cost conscious climate the ultimate criteria is the total cost of hole production. This figure will be dependent on a broad range of factors, some external to the rig operation and others highly dependent on the drilling parameters selected by the rig operator. The drilling parameters are all highly interdependent and are also influenced by external factors, often unknown and beyond the control of the operator. The application of a control scheme in such an environment is fraught with difficulty.
As an alternative and simpler control parameter, the current cost per unit distance drilled is convenient. Minimising the cost per unit distance may not necessarily give a true minimum cost to completion, in view of unpredictable future elements which may be met in the drilling process but this does provide a basis for a useful control system.
The variable costs involved are highly dependent on the performance of the drilling operation which is controlled by the nature and condition of the strata, the bit and the drilling parameters selected by the rig operator. Most of these costs exhibit a time dependence and include:
Manpower
The manpower requirements depend to a large extent on the size and complexity of the drilling operation. This in turn is determined by the depth and application of the hole. The size of rig crews vary from single operator small rigs up to crews of seven or more for large land based rigs.
A typical crew for a large rig might be made up from;
In addition there will probably be a drilling superintendent who may have control over several site operations. The actual cost of manpower varies considerably with location, typically in Europe they may make up around 12% of the total cost (4). The contribution of manpower to the total cost can be considered on a per unit time basis, and as such is directly related to the rate of progress of the hole. It should be noted that the rate of progress must include consideration of both the rate of penetration and the tripping times.
Consumables
Fuel costs are a function of both the total time to completion and the power requirements for rotation and circulation. the fuel cost may be minimised by maintaining good cutting efficiency which will generally yield high penetration rates. For any given rock type, drilling parameters can be chosen which yield a minimum power requirement per unit distance drilled. These performance figures are directly related to the Specific Energy of the rock.
Mud costs are mainly dependent on the strata type, depth and hole condition. These are mostly beyond the control of the driller, however the correct selection of mud properties and circulation rates is critical to the success of the operation.
The unit cost of tools is
REFERENCES:
patent: 4346444 (1982-08-01), Schneider et al.
patent: 4407017 (1983-09-01), Zhilikov et al.
patent: 4854786 (1989-08-01), Alexander et al.
"The Concept of Specific Energy In Rock Drilling," R. Teale, Int. J. Rock Mech. Mining Sci., vol. 2, pp. 57-73, Pergamon Press 1965.
"Performance and Wear Characteristics in Diamond Core Drilling", Cassapi et al., Drillex '87 Conference, Warwickshire England, Apr. 7-10, 1987.
"Drilling Practices Manual," Second Edition, Preston L. Moor, Pennwell Publishing Company, 1974, pp. 17-21.
Rowsell Philip J.
Waller Martin D.
Bui Thuy M.
University of Nottingham
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