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Directional Well Plan

A variety of data go into the design of a directionally drilled well, including the depth and distance from the surface location to each subsurface target, diameter of the target, KOP, build rate, platform location, lease lines, hole size, and total depth of the well. Once preliminary studies indicate the need for a deviated well, most companies rely on a directional drilling service company to prepare the final directional plan.

A directional well design consists of both vertical and horizontal plans. Figure 3-13 shows the horizontal and vertical plans for the Diamond Shamrock Well No. 1. Reviewing Figure 3-13a, we see that the KOP for this well is about 950 ft MD, and the build rate averages about 2 deg per 100 ft to a maximum deviation angle of 45°30' at a MD of 4800 ft. Figure 3-13b shows the horizontal plan for the well. The plane of the proposed direction is south 46°25' west from the surface location with the bottomhole location (BHL) 10,873 ft from the surface location. The well is drilled to a MD of 19,484 ft, which is equal to a TVD of 15,695 ft.

FIGURE 3-13

Figure 3-13 (a) Vertical section plan for a directional well. (b) Horizontal plan for the same directional well shown in Figure 3-13a. (Published by permission of Gardes Directional Drilling.)

A grid reference for north is shown in Figure 3-13b. Several coordinate systems exist for industry’s use and, unfortunately, it is common for the data sources (e.g., directional well surveys and seismic surveys) and maps used in a project to be in different coordinate systems. It is critical that all of them be converted to the same system to reduce errors in location.

Figure 3-14 illustrates the vertical plan for a well that has a maximum deviation angle of 94 deg and a maximum build angle of 14 deg per 100 ft. The wellbore is vertical near the surface, and at a depth of 1659 ft (TVD), it is horizontal.

FIGURE 3-14

Figure 3-14 Vertical plan for a nearly horizontal well with a maximum deviation angle of 94 deg. (Published by permission of Gardes Directional Drilling.)

Commonly, deviated wells are drilled with a build rate of 2 deg per 100 ft of hole drilled. Figure 3-15 shows the scaled chart for a 2 deg per 100 ft build rate. Such charts are used to make a quick estimate of well design after structure maps have been made on target horizons. For example, from the chart, a target horizon located at a TVD of 10,000 ft and a horizontal distance of 4000 ft from the platform location requires the drilling of a well with a deviation angle of approximately 23 deg to a MD of 10,800 ft. Such charts are available from directional service companies for build rates ranging from 1 deg to 5 deg per 100 ft. In most cases today, however, these charts have been replaced with computer software that can calculate preliminary directional plans quickly.

FIGURE 3-15

Figure 3-15 Scaled chart for a build rate of 2 deg per 100 ft of hole drilled. (Published by permission of Eastman Christensen.)

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