Until recently, directional drilling was considered prohibitively challenging and expensive compared to conventional methods. Improvements in technology have diminished many of these obstacles, however, and directional drilling is now a valuable approach in many circumstances. This article describes areas of historic concern for directional drilling, along with improvements that have helped make angled wells a viable option.

What Is Directional Drilling?

Directional drilling is the practice of digging a well at an incline, rather than boring straight up and down. There are a number of scenarios where angled drilling offers significant advantages, such as when a reservoir is difficult to access from directly above. An example would be when an oilfield is located beneath a city or lake.  

Directional drilling can also offer greater exposure to a reservoir because the bore can follow the reservoir transversely, rather than simply dropping through it. Another reason directional drilling may be desired is because if wells are drilled at an angle, then the wellheads can be grouped closely together, rather than spread out over the top of the reservoir. Clustering the wellheads can mean saving money because it involves fewer rig moves. It also can reduce the environmental impact of the wells because there is less surface area that's been disturbed by the process.

Slower Drilling

Despite these obvious advantages, the prominence of directional drilling has been tempered by a number of disadvantages until recently. First among these is the speed of drilling. The rate of penetration (how fast a drill can proceed through the ground) has traditionally been much slower for non-vertical well. Thanks to the arrival of modern, highly efficient, downhole motors, the speed of drilling is no longer a serious drawback.

Surveying

Another concern that plagued directional drilling for years was the increased need for survey work. Knowing how far the wellbore deviates from vertical (the inclination of the hole) and how far it deviates from the horizontal (the azimuth) are critical in directional drilling. And while determining the inclination can be done with relative ease by using a pendulum, the azimuth has traditionally be difficult to ascertain.  he invention of small gyroscopic compasses over the last century has greatly simplified this determination and it is now possible to perform semi-continuous surveying, greatly reducing this burden.

Sand Influx at Shallow Angles

A final difficulty that has recently been reduced is the increased operational difficulties when a well is drilled at a shallow angle. When the inclination is less than 40 degrees, preventing sand influx into the well is relatively simple. Unfortunately, as the angle of the well becomes increasingly shallow the likelihood of sand influx increases. Needed tools must also be "pushed" into the well, rather than relying strictly on gravity. Although the costs associated with addressing these concerns is still higher than in vertical counterparts, advances both in technology and drilling theory have made it possible to carry out the needed maneuvers reliably with adequate "sand planning."

Many factors are important in deciding whether directional drilling is the right choice to access a particular reservoir. Thanks to the improvements described in this article, however, many traditional disadvantages to angled boring should no longer be considered critical factors in making that decision. 

For more information, contact a company like HDD Full Bore Directional Inc.

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