Rotary drills

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 ... 

In today s operations a mud motor or a mud turbine are mostly used for directional drilling. Rotary drilling may be carried out between mud motor / turbine drilling i.e. the use of these is often restricted to a certain interval only. 

Production and Consumption. About 80% of the world s barite production is used as a weighting agent for the muds ckculated in rotary drilling of oil and gas wells (see PETROLEUM, DRILLING FLUIDS AND OTHER OIL RECOVERY CHEMICALS). Table 2 shows the U.S. production—consumption balance. The 1988 demand for barite increased nearly 40% over that recorded in 1987. However, by the end of 1988, oil prices had declined and renewed economic uncertainties depressed exploration and development activity. Barite demand fell accordingly and imports of lower cost foreign product exceeded domestic production. 

Moore, W. W., Eundamentals of Rotary Drilling Energy Publications, 1981. 

The drawworks does not carry out only hoisting functions on the rotary drilling rig. In general, the functions of the drawworks are as follows ... 

Hoisting, service Other thari rotary drilling ... 

Rotary drilling. line when settirig casing. slIifllliyfflliislilitelM... 

Rotary Drilling Line Service-Record Form... 

Figure 4-81 is a rotary drilling line service-record form. It can be filled out on the bases of Figure 4-82 and previous discussion. 

Slipping and Cutoff Practice for Rotary Drilling Lines... 

The values given in Figure 4-84 are Intended to serve as a guide for the selection of Initial ton-mile values as explained in Par. "Service Goal." These values are conservative, and ate applicable to all typical constructions of wire rope as recommended for the rotary drilling lines shown in Table 4-9. 

Cutting in on drum. Loose winding on drum. Improper cutoff and moving program for rotary drilling lines. Improper or worn drum grooving or line turnback plate. 

Mud pumps consume more than 60% of all the horsepower used in rotary drilling. Mud pumps are used to circulate drilling fluid through the mud circulation system while drilling. A pump with two fluid cylinders, as shown in Figure 4-99, is called a duplex pump. A three-fluid-cylinder pump, as shown in Figure 4-100, is called a triplex pump. Duplex pumps are usually double action, and triplex pumps are usually single action. 

During normal rotary drilling processes, due to frictional pressure losses, the pressure inside the drill string is greater than that of the outside drill string. The greatest difference between these pressures is at the surface. 

Rotary drilling bits are classified into the following types ... 

In 1873, an American, C. G. Cross, was issued the first patent related to a downhole turbine motor for rotating the drill bit at the bottom of a drillstring with hydraulic power [78]. This drilling concept was conceived nearly 30 years before rotary drilling was introduced in oil well drilling. Thus the concept of using a downhole motor to rotate or otherwise drive a drill bit at the bottom of a fluid conveying conduit in a deep borehole is not new. 

A typical MWD bottomhole assembly used in rotary drilling is as follows from bottom to top drill bit, stabilizer, resistivity, WOB torque, directional and telemetry system, neutron-density Pe. The typical distances are seen in Figure 4-296a. When a mud motor is inserted between the lower stabilizer and the drill bit, the distances are increased as shown in Figure 4-296b. 

Figure 4-296. Typical MWD bottomhole assemblies (a) rotary drilling (b) mud motor drilling.

The factors that influence the rate of penetration during a conventional rotary drilling process are numerous. In general these factors can be classified into five groups. 

J. Rotary drilling inside casing. Setting the casing with improper tension after cementing is one of the greatest contributing causes of such failures. 

The rotary drill bits are generally made from quench and tempered steel alloys such as AISI 3115 to 3120, 4620, 4815 to 4820 and 8620 to 8720. The only corrosion related problem that can arise may result from a hydrogen sulfide environment. The bearing in the roller rock bits can be damaged by H S contamination of drilling fluid. However, a well conditioned drilling fluid at... 

The basic principles of rotary drilling defined for onshore operations are also applicable to offshore operations. The primary difference offshore is that a stable, self-contained platform must be provided for the drilling equipment. Communication with a well through possibly thousands of feet of water provides for mechanical as well as procedural differences, primarily in well control. Onshore technology can be applied to offshore operations in many instances on bottom-supported rigs, but the use of floating vessels has resulted in the development of new technology tailored to the offshore environment. 

API Specification 7 API Specification for Rotary Drilling Equipment, Dallas, December 1981. 

API Bulletin DIO, Second Edition Procedure for Selecting Rotary Drilling Equipment, API, Dallas, January 1982. 

A. Nicholson, R. W., Minimize drill pipe damage and hole problems. Follow acceptable dog-leg severity limits, transactions of the 1974 lADC Rotary Drilling Conference. 

Reed, P., Amerada develops special rotary drill stem for simultaneous electrical logging and drilling, Oil and Gas J., pp. 68-70, Nov. 17, 1939. 

API Specification 7, Thirty-Fourth Edition Specifications for Rotary Drilling Equipment, May 1984. 

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