Drilling operation

Unless the workpiece is held in a drill jig, the position of holes on a workpiece must be marked out. When the position of a hole is determined, its centre is indicated by means of a centre dot, using a centre punch. This centre dot is used to line up the drill and as a means of starting the drill in the correct position. The workpiece is set on the worktable, carefully positioned under the drill, using the centre dot, and clamped In position as shown in Fig. 8.19. Two clamps are usually required, one at each side of the component. 

When held in a vice, the workpiece should be positioned and the vice be tightened securely. The workpiece is then positioned under the drill as before and the vice is clamped to the worktable. 

In positioning the workpiece, take care to avoid drilling into the vice or worktable. If necessary, raise the workpiece on parallels. Fig. 8.19. 

Before drilling, check if the drill is the correct size. Because you remove it from a space marked 5 mm does not mean it is a 5 mm drill -the person who used it before you may not have returned it to the correct space. Also, check the condition of the cutting edges and if necessary resharpen them. 

Where the chisel edge is found to be too wide for a particular purpose, it can be reduced by point thinning. Fig. 8.20. This can be done using the edge of a well-dressed grinding wheel, but it is perhaps better left to a more experienced person. 

When held in a vice, the workpiece should be positioned and the vice be tightened securely. 

The workpiece is then positioned under the drill as before and the vice is clamped to the worktable. 

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This first information about the reservoir is recorded, as a function of depth, in the form of several columns. Although rather qualitative in many respects, mudlogging is an important data gathering technique. It is of importance as a basis for operational decisions, e.g. at what depth to set casing, or where to core a well. Mudlogging is also cheap, as data is gathered while the normal drilling operations go on. 

Estimated cost casing drilling operation well equipment TOTAL Estimated rig time 000 200 2000 400 2600 28 days Type of well Deviated, oil, development Drilling rig Jolly Roger-1 Datum Level DFE 88ft above MSL Sea Bed 250ft Total Depth 3700ft Conductor No No.8 ... 

Drilling Jackets are small steel platform structures which are used in areas of shallow and calm water. A number of wells may be drilled from one jacket. If a jacket is too small to accommodate a drilling operation, a jack-up rig (see below) is usually cantilevered over the jacket and the operation carried out from there. Once a viable development has been proven It is extremely cost effective to build and operate jackets in a shallow... 

Whether onshore or offshore drilling is carried out, the basic drilling system employed in both cases will be the rotary rig (Fig. 3.7) and the following summarises the basic functions and parts of such a unit. Three basic functions are carried out during rotary drilling operations ... 

During drilling operations sometimes large volumes of drilling mud are lost into a formation. In this case normal mud circulation is no longer possible and the fluid level inside the borehole will drop, creating a potentially dangerous situation as described below. The formations in which lost circulation can be a problem are ... 

If a situation arises whereby formation fluid or gas enters the bore bole the driller will notice an increase in the total volume of mud. Other indications such as a sudden increase in penetration rate and a decrease in pump pressure may also indicate an influx. Much depends on a quick response of the driller to close in the well before substantial volumes of formation fluid have entered the borehole. Onoe the BOP is closed, the new mud gradient required to restore balance to the system can be calculated. The heavier mud is then circulated in through the kill line and the lighter mud and influx is circulated out through the choke line. Once overbalance is restored, the BOP can be opened again and drilling operations continue. 

Fig. 3.24 shows the cost breakdown of a typical development well. As can be seen, drilling operations are the area with the largest scope for cost savings. The actual costs of a well show considerable variations and are dependent on a number of factors, e.g. ... 

This type of contract requires the operator to pay a fixed amount to the contractor upon completion of the well, while the contractor furnishes all the material and labour and handles the drilling operations independently. The difficulty with this approach Is to ensure that a quality well Is delivered to the company since the drilling contractor will want to drill as quickly and cheaply as possible. The contractor therefore should guarantee an agreed measurable quality standard for each well. The guarantee should specify remedial actions which will be implemented should a substandard well be delivered. 

As the name implies the company basically rents the rig and crew on a per day basis. Usually the oil company also manages the drilling operation and has full control over the drilling process. This type of contract actually encourages the contractor to spend as much time as acceptable on location . With increased cost consciousness, day rate contracts have become less favoured by most oil companies. 

Coring is performed in between drilling operations. Once the formation for which a core is required has been identified on the mud log, the drilling assembly is pulled out of hole. For coring operations a special assembly is run on drill pipe (Fig. 5.33) comprising a core bit and a core barrel. 

The first function of a wellsite is to accommodate drilling operations. However, a wellsite must be designed to allow access for future operations and maintenance activity, and in many cases provide containment in the event of accidental emission. Production from a single wellhead or wellhead cluster is routed by pipeline to a gathering station, often without any treatment. In such a case the pipeline effectively becomes an extension of the production tubing. If a well is producing naturally or with assistance from a down... 

Fraser, Ken (1991) Managing Drilling Operations, 246p, Elsevier... 

In instances where test bores have been completed, it may sometimes be possible to predict the general locations of productive fractures. When these are encountered by surprise, however, the appropriate adjustments in the drilling strategy must be implemented rapidly, slowing the progress of the drilling operation and increasing the costs. 

The greatest amount of surfactant consumption is in packaged soaps and detergents for household and industrial use. The remainder is used in processing textiles and leather, in ore flotation and oil-drilling operations, and in the manufacture of agricultural sprays, cosmetics, elastomers, food, lubricants, paint, pharmaceuticals, and a host of other products. 

Applications. The high heat tolerance and good salt compatibiUty of welan gum indicate its potential for use as an additive in several aspects of oil and natural gas recovery. Welan also has suspension properties superior to xanthan gum, which is desirable in oil-field drilling operations and hydraulic fracturing projects. It is compatible with ethylene glycol, and a welan—ethylene glycol composition that forms a viscous material useful in the formulation of insulating materials has been described (244). 

Chemical additives for gas-based drilling fluids are limited to surfactants (qv), certain polymers, and occasionally salts such as sodium or potassium chloride. An aqueous solution of the additives is iajected iato the air or gas flow to generate a mist or foam. No additives are used ia dry air or gas drilling operations. Gas-based fluids are not recirculated and materials are added continuously. As the fluid exits the well, air or water vapor escapes to the atmosphere, gas and oil are burned, and water and formation soflds are collected into a pit for later disposal. Stable foams must be destabili2ed to separate the air from the Hquid phase for disposal. 

How well the drilling fluid fulfills these functions is determined primarily by the response of the well. The whole drilling operation suffers if the fluid is not adequate. In extreme cases, drilling may be stopped or a hole may have to be redfilled. A variety of physical and chemical properties are monitored to ensure satisfactory performance and guide fluid formulation and treatment (21,22). 

The chemical and mechanical dispersion of the drilled soHds tends to increase the percentage of smaH-sized soHds in a mud as drilling progresses. The incorporation of a limited amount of drilled soHds (several volume percent) is an economical way of increasing the density of low density muds, but it also reduces penetration rates hence, drilled soHds are usually kept to a minimum. The common clay and formation soHds encountered in normal drilling operations are as foUows ... 

Natural Deposits. Natural deposits, eg, minerals and fossil fuels, are located by drilling operations. An auger, eg, a screw or worm, is turned in the earth and pulled out, and material is scraped from the auger for analysis. Alternatively, samples can be taken by hoUow core drills which, when withdrawn, enclose a core of the earth that is representative of the strata through which the drill has passed. Such core samples are used in geological surveys for fossil fuels. As the drill drives deeper into the strata, each core is extracted and placed in a shallow box and coded so that a complete cross section of the geological strata can be reconstmcted. From this, the relative thickness of coal and mineral seams can be directly measured. 

It generally is recommended, and often required, that gas dcicciiuii systems be installed in a fail-safe manner. That is, if power is disconnected or otherwise interrupted, alarm and/or process equipment shutdown (or other corrective action) should occur. All specific systems should be carefully reviewed, however, to ensure that non-anticipated equipment shutdowns would not result in a more hazardous condition tlian the lack of shutdown of the equipment. If a more hazardous situation would occur with shutdown, only a warning should be provided. As an example, a more hazardous situation might occur if blowout preventers were automatically actuated during drilling operations upon detection of low levels of gas concentrations than if drilling personnel were only warned. 

Figure 5.10 shows a detailed fault tree for an offshore drilling operation. The top event of the fault tree is Failure to use shear rams to prevent blowout. As wi the fault tree in Figure 5.2, the representahon combines both hardware... 

Oil Spills. Oil spills occur from oil pipeline leaks, oil tanker accidents, or submarine oil drilling operations. The two major ocean drilling accidents—oil wells blowing out—were the 1969 Santa Barbara Channel spill and the 1979 Yucatan Peninsula spill, in Mexico. The Yucatan spill spewed out more than three million barrels before being capped in 1980. Both caused damage to beaches and marine life, but the smaller Santa Barbara spill was far more devastating because of unfavorable winds following the accident. 

Depending on the depth of the well, this time lag can consume valuable time needed to address the problem—either technical or geological—before it becomes worse and/or causes drilling operations to stop. Drilling a well involves all types of technical, geological, and economic risks. The greatest economic risk occurs when drilling operations must be... 

After the surface casing has been tested and the blowout preventer installed, drilling operations are resumed. They will continue until the well has been drilled to the total depth decided upon. Usually the... 

Wlien seas are less treacherous and there is greater need for mobility and flexibility, the drill ship is preferred over the semisubmersible. The drill ship has a derrick mounted in the middle over an opening for drilling operations, with several moorings used to hold the ship in position. 

The oil and gas lease under homestead law would simply be the right to conduct drilling operations on a person s surface property. The lease would not constitute a claim to minerals found under a particular surface area as under the rule of capture rule. Since the resci voir could be reached from different surface locations with slant drilling, the economic rent of a homestead lease would be far less than the value of a capture-rule lease. The difference in value would accrue to the driller-finder, thereby encouraging production by making drilling more efficient and profitable. 

Pumps are a very essential part of the oil and gas industry. They are used throughout the industry, from drilling operations through to final delivery to the customer. 

Compressors of various designs and manufacturers are used in many operations throughout the oil and gas industry. Compressors are used in some drilling operations, in many production operations, and extensively used in surface transportation of oil and gas via pipelines. 

During drilling operations, it is advisable to make scheduled inspections of all bolted connections to ensure that they are tight. 

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