Curved Well Conductors and Offshore Platform Hydrocarbon Development
Authors: Cox B.E. , Bruha W.A. 
Published: October 2008

Since 1970, technology has been developed relative to drilling offshore platform directional wells with conventional equipment through curved conductor pipes. Curves and graphs are presented which compare the lateral reach characteristics of directional wells through curved and vertical pipes. Planning considerations and experience in driving and drilling through curved conductors are discussed. Technical and operational considerations in platform and well design are discussed. Illustrations of curved conductor installations on platforms in 190' to 305' of water are presented. Well trajectory, directional drilling data, and tubular information illustrate the degree of success achieved in reaching objectives by drilling wells through curved conductors. Conclusions are based on experience with installing 69 curved conductors and drilling wells through 22 of these conduits.

INTRODUCTION

The 1970 Federal Offshore Louisiana Lease Sale brought with it the requirement to develop shallow depth hydrocarbons from sites covered with 150 to 400 feet of water. Since the lateral reach of a conventional vertical conductor was very limited in the 3500 to 6000 ft. depth range, several platforms would be required to cover these prospects. The potential for extended lateral reach prompted a review of unconventional methods which would improve platform well reach. (The term conductor used in this paper refers to the part of the well tubulars often called drive pipe.)

Figure 1 illustrates the reach improvement obtained when the rate of building drift angle increases from 2 to 4 degrees per 100 feet (55 degrees maximum). The building of angle faster below the conductor improves the coverage of vertical conductors by a noticeable amount as evidenced by area factor values on Figure 1. Initiating well deflection above the water instead of below the conductor also has a spectacular improvement in reach.

Discussions with drilling engineers led to the concept that a well could be drilled around a curve of 6 degrees per 100 feet if the curvature was smooth and drill string weight below the curvature minimized. This rapid increase in drift angle through the 150 to 400 ft. water zone of an offshore platform can improve the mud line drift angle by 9 to 24 degrees, respectively. When angle improvement above mud line is combined with that below the mud line, the curved conductor becomes a very useful tool. This method was evaluated with a successful field test well in 1970.

WELL PLANNING CONSIDERATIONS

Generally, curved conductors are most advantageous in water depths over 150' when developing hydrocarbon reservoirs shallower than 7,000 true vertical depth. They have applications not only in conventional rig development drilling, but exploratory drilling from platforms under conditions that could normally require the more expensive mobile rigs.

The improved reach characteristics of curved conductor will have a significant impact on the choice of platform sites. Locations may be selected at some distance off the center of hydrocarbon accumulation in order to avoid surface and near-surface obstructions such as: salt plugs, shallow faults, sea bed reef deposits, gas seeps, shallow gas pockets, mud slides, debris, and shipping fairways.