Derrick

In preparation for a field wide quick look correlation, all well logs need to be corrected for borehole inclination. This is done routinely with software which uses the measured depth below the derrick floor ( alonghole depth below derrick floor AHBDFor measured depth , MD) and the acquired directional surveys to calculate the true vertical depth subsea (TVSS). This is the vertical distance of a point below a common reference level, for instance chart datum (CD) or mean sea level (MSL). Figure 5.41 shows the relationship between the different depth measurements. 

The data refer to various temperatures between 18 and 25°C, and were compiled from values cited by Bjerrum, Schwarzenbach, and Sillen, Stability Constants of Metal Complexes, part II, Chemical Society, London, 1958, and values taken from publications of the lUPAC Solubility Data Project Solubility Data Series, International Union of Pure and Applied Chemistry, Pergamon Press, Oxford, 1979-1992 H. L. Clever, and F. J. Johnston, J. Phys. Chem. Ref Data, 9 751 (1980) Y. Marcus, Ibid. 9 1307 (1980) H. L. Clever, S. A. Johnson, and M. E. Derrick, Ibid. 14 631 (1985), and 21 941 (1992). 

Derrick Type Stack - This type of unit is well-suited for tall structures subject to strong winds. However, derrick type stacks are the most expensive to erect and maintain. 

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. 

Standard Derricks 501. Load Capacities 506. Design Loadings 508. Design Specifications 511. Maintenance and Use of Drilling and Well Servicing Structures 515. Derrick Efficiency Factor 521. 

The derrick or mast must also be designed to withstand wind loads. Wind loads are imposed by the wind acting on the outer and inner surfaces of the open structure. When designing for wind loads, the designer must consider that the drill pipe or other tubulars may be out of the hole and stacked in the structure. This means that there will be loads imposed on the structure by the pipe weight (i.e., setback load) in addition to the additional loads imposed by the wind. The horizontal forces due to wind are counteracted by the lattice structure that is firmly secured to the structure s foundation. Additional support to the structure can be accomplished by the guy lines attached to the structure and to a dead man anchor some distance away from it. The dead man anchor is buried in the ground to firmly support the tension loads in the guy line. The guy lines are pretensioned when attached to the dead man anchor. 

For modern derrick and mast designs, API Standard 4F is the authoritative source of information, and much of this section is extracted directly from this standard. Drilling and well servicing structures that meet the requirements of API Standard 4F are identified by a nameplate securely affixed to the structure in a conspicuous place. The nameplate markings convey at least the following information ... 

The following terms are commonly used in discussing derricks and masts ... 

Crown block assembly The stationary sheave or block assembly installed at the top of a derrick or mast. 

Derrick A semipermanent structure of square or rectangular cross-section having members that are latticed or trussed on all four sides. This unit must be assembled in the vertical or operation position, as it includes no erection mechanism. It may or may not be guyed. 

Guy line A wire rope with one end attached to the derrick or mast assembly and the other end attached to a suitable anchor. 

Height of derrick and mast without guy lines The minimum clear vertical distance from the top of the working floor to the bottom of the crown block support beams. 

A standard derrick is a structure of square cross-section that dimensionally agrees with a derrick size shown in Table 4-1 with dimensions as designated in Figure 4-1. 

Derrick Height Base Square Window Opening Opening Opening Clearance ... 

The derrick window arrangement types A, C, D, and E, shown in Figure 4-2, shall be interchangeable. The sizes and general dimensions of the V window opening and drawworks window opening are given in Tables 4-1 and 4-2. 

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