Directional drilling in the Oil & Gas industry is a technique used to drill deviated and/or horizontal wells, as well as wells with multiple angles. In addition, directional drilling allows drilling multilateral wells from the same horizontal wellbore, reach multiple targets, as well as drill multiple wells from the same location, which in turn saves time and cost, compared to the standard way of accessing an oil reservoir. With “easy oil” being in the past, drilling into reservoir sections become more and more challenging and complex. Tremendous improvements in the technology behind directional drilling allow the industry to geo-steer a well in real-time and achieve very high inclination and angles.
Directional drilling services are divided into two distinctive "technologies" - Rotary Steerable Systems (RSS) and Down-hole Motors.
A Rotary Steerable System (RSS) is a technology employed when drilling directional wells, both onshore and offshore. Today, RSS systems became very sophisticated and able to drill high angle inclination and long horizontal wells. Using measurement while drilling (MWD) technology, engineers on the surface can change the angles and direction of the wellbore, by steering ( geosteering) the well using the RSS system. RSS systems use the rotation of the drill pipe, with geo-steering achieved using 1) pushing-the-bit and 2) pointing-the-bit. When a drill bit is pushed (push-the-bit) in order to achieve well inclination, side forces ( hydraulic or mechanical) are applied to the bit and pushed against the borehole, hence pushing the bit in the opposite direction of the force. In the Point-the-bit approach, a bent-housing or a shaft inside the body of the RSS system is used to change the direction, whereby the front part ( face) of the RSS system changes its orientation against the axis of the drill string.
All RSS systems use continuous rotation from the drilling rig equipment on the surface. This continuous rotation of the drill string also improves the transportation of drill cuttings, generated as a result of "cutting" the earth when drilling. In addition, it provides superior formation evaluation data, as the walls of the well are smoother, as a result of a more balanced well trajectory. RSS systems can also be run below down-hole motors to have better performance. Some directional wells are very challenging or even impossible to drill without having the RSS system.
Down-hole Motors / steerable motor assemblies (positive-displacement motors (PDM). When steerable motor assemblies are used, the power to the bit is provided by a mud-motor (positive displacement motor) and assembly of deviation tools, such as bent sub or bent housing. Steering is achieved by using a similar approach as with the point-the-bit system, whereby a drill bit changes its orientation against the axis of the drill string. Motors have very little surface rotation with the drill string; as such chances of down-hole problems are higher when it comes to sticking and transport and removal of drill cuttings.
Generally, RSS is used in geological formations where precise directional control is required. A motor (high-performance mud motor) can be used in less complex formations, providing a better overall cost of drilling. A combination of both may exist in certain applications.
Quick Facts about two major directional drilling technologies
The majority of equipment used in directional drilling services is patented to major service providers. The fundamentals of the technology are mainly around 1) how to achieve inclination and control of the drill bit and bottom-hole-assembly (BHA) and 2) acquire data in real-time data and send it to the surface. While the basic technology behind the tools is similar, the superiority of one over the other depends on the application and environment. Modern days, directional drilling tools allow to navigate and geo-steer a well, using real-time data and sophisticated visualization techniques, as down-hole data is acquired in almost real-time.
Directional drilling tools are also required to collect information and get it to the surface, to understand what is happening subsurface, as the well is being drilled. Major families of equipment, based on various logging and measuring principles, are Logging-While- Drilling (LWD), Measurements-while-drilling (MWD) and Formation evaluation while drilling. A very high-end and precise technology used to collect and analyze data, which is then used for Reservoir, Petrophysics, Geology, Geomechanics, Geophysics and Reservoir Engineering. The data is also used for well placement, positioning, and anti-collision applications, where multiple wells are drilled in close proximity to each other. Depending on the well type, there may be only MWD or a combination of MWD, LWD, and others used as a full suite of tools. For example, drilling an injector well, costly LWD tools may not be required, as there is no reservoir data to be collected and analyzed. Yet, there might be cases where this LWD may be required for continuous reservoir study and monitoring.
On average, Directional Drilling services represent between 5 to 15% of a well cost. Due to increased complexity in drilling, the services become more critical to operators, as such switching costs and learning curve costs could be very high.