Most people would assume that when drilling for water, oil, natural gas, or other subsurface objects that they are targeted vertically — drilled straight down into the earth. However, this traditional method of drilling has been largely replaced.
In the current day, drilling a hole in the ground can consist of complex geometry including builds, turns, and tangents to construct a well. The well can be either geometrically or geologically steered. Geometric steering involves adjusting the position of the wellbore based on a pre-arranged plan and then using complex measurements and surveys to stay on that plan. Geological steering involves orienting the wellbore based on the properties of the lithology being drilled into to “find” the right reservoir rock.
It is important to discuss why directional or horizontal drilling can be not only beneficial but necessary, reasons include:
- Unreachable deposits: it may be sometimes deemed obligatory to go around obstacles by using directional or horizontal drilling. There could be a variety of barriers that prevent access, such as difficult rock formations, utility lines under the surface, residential areas, or sensitive ecosystems. This allows oil companies to drill away from these obstacles or hazards to make it a more sensible, practical, or environmentally friendly option.
- Increased operational efficiency: Having the ability to access and drain larger parts of the reservoir from a single pad is a huge advantage of directional drilling. This decreases surface disturbances and also saves money and time with the reduction of well pad setups. Grouped wellheads also allow for fewer rig moves, which in turn saves more time and money.
- Increased reservoir production: Directional or horizontal drilling can expose the well to the maximum amount of the reservoir or allow the well to cross the largest number of fractures to increase production.
- Relieve pressure: Directional drilling can help relieve the pressure from out of control wells. Pressure can be relieved from one well by tapping the same well at an angle with another well. These relief wells are drilled at a safe distance away from the blowout but come in to intersect the troubled wellbore.
Directional drilling can cost up to 300% more than vertical drilling, but the potential increases in efficiency along with lowered production cost makes this drilling technique more financially viable.
Ulterra Drilling Minute Video: Directional Drilling Operations
Directional Drilling: A Brief History
Directional drilling dates back to the 1920’s with the advent of techniques for surveying the angle and direction of a drilled well. Prior to this, wells were intended to be constructed vertically but were subsequently found to have deviated quite far from that. The first intentionally deviated wells were drilled in the late 1920’s into the 1930’s by using hardwood, and then steel wedges called whip stocks that were lowered into the hole at a specific angle to force the drill bit in a certain direction. Through the 1940’s and 50’s, various techniques that still exist today were developed, including designing the drilling assembly to bend in a particular way and also jetting (using an oriented large nozzle on the bit to wash away rock in the preferred direction).
In the 1950’s, downhole drilling motors, or mud motors, were developed. These mud motors use fluid flow through the assembly, converting hydraulic energy into mechanical energy to drive the drill bit independently from the rest of the drilling string. A fixed angle could then be put into the assembly which could be oriented and held in the desired direction while the bit still drills ahead. Using a mud motor with the use of a measuring while drilling tool (MWD), a directional driller has the capability to steer the drill bit to the desired zone. The data collected from the MWD tool helps the operator monitor and manage the direction of the bit, obtain records, and generate survey reports. By the time the 1970’s rolled around, mud motors had taken over directional drilling and they firmly remain as the preferred method of directionally drilling a well.
The next major advancement in directional drilling was the creation of rotary steerable (RSS) tools, which allow 3D control and steering of the drill bit without stopping the drill rotation. These tools are directly controlled from the surface using advanced communication techniques, and they either push the bit or point the bit in the required direction in real time. Directional drilling has vastly improved with technological advancements, especially toward a less time-consuming drilling process. These advances have also allowed for greater success and precision in the drilling process. New digital technology has made the collection of data much easier and allowed drilling operations to be better planned beforehand and controlled during the drilling process.
Types of Direction Drilling
When speaking about directional drilling, it is commonly assumed that one is referring to horizontal well drilling, which is a method of deviating the well until it is at, or close to a 90° angle from the vertical in order to drill out sideways and along a specific layer of rock. There are a few other directional drilling methods that will be discussed below.
- Horizontal Drilling: The trajectory of a wellbore starts vertically then steers horizontally at depth for thousands of feet. This allows increased contact between the well and the reservoir to increase productivity. It also provides access to reservoirs that are too thin to be accessed by vertical drilling.
- Multilateral Drilling: A single wellbore creates a trunk and then many branches stem from it, increasing production from a single drilling site. This drilling technique increases the contact area and allows for many branches to produce from the same well. These can be horizontal, curved slightly to one side, or turned sharply to form a J-type well. Multilateral drilling can occur in either new or existing oil and gas wells and typically includes two laterals. The main benefit of using this drilling approach is the increased efficiency and reduced cost of tapping multiple reservoir locations from a single point.
- Extended Reach Drilling (ERD): To figure out if the well is considered an ERW, calculate the ratio of horizontal departure to vertical depth. If the depth ratio is greater than 2, the well is considered an Extended Reach Well (ERW). An ERW can be relatively long and deep, short and shallow, or something in between. The benefit of ERD is the increase in efficiency by exposing the open hole to long sections of the reservoir rock, or by crossing through multiple reservoirs in one long wellbore. It is expensive and risky but it is sometimes the best option available. With advances in technology, these wells are getting longer and longer as we get better at overcoming the challenges of managing downhole pressure, managing and controlling the mechanical loads on the drill string, and hole cleaning.
- Coiled Tubing Drilling (CTD): Coiled tubing refers to a specific type of small diameter, long, continuous metal pipe rolled on to a giant reel (the coil) that can be used as a drilling assembly to reenter and extend a previously drilled hole, drill out from it in a different direction, or perform remedial work to get the well flowing efficiently again. Although drilling using a small flexible pipe has its own challenges, particularly when it comes to directional control, it can be done relatively inexpensively and fast.
- Through Tubing Rotary Drilling: This is an expensive way to create a shorter length sidetrack of an existing well. This can be done after a well has already been constructed and used, but requires more reservoir to increase production. This is a great method to revitalize old reservoirs that were previously tapped using vertical holes that could also benefit from the horizontal exposure of the reservoir. A hole is cut in the steel pipe that lines the wellbore and then a steel whip stock is set in place and used to push the drilling assembly sideways out of the side of the well. This technique is also used to explore deep layers of rock below the target reservoir, before casing it off and using the same wellbore to access the main target.
Path of a Drill Bit
Directional wells carry various economic and safety benefits. Economically speaking, directional drilling increases the access to a reservoir, increases hydrocarbon recovery, increases the well count number from one location, and reduces rig move costs. Although directional drilling could be as much as three times more expensive than vertical wells, the higher production rates and efficiencies offset the expensive process. The combination of fracking with cutting-edge technologies and horizontal drilling has caused a huge surge in the oil and natural gas production in the United States, particularly in major oil and gas regions such as the Permian Basin, Eagle Ford Shale, and the Bakken Shale.
Directional wells should be meticulously planned in advance and flawlessly executed in order to manage the additional costs. A directional plan is created prior to drilling commences, which outlines the position of the well precisely under the surface of the earth. It typically contains specific targets in 3D space that the drilling assembly must hit in order to contact the reservoir at the optimum point, as well as specific changes in angle required to hit those targets. The directional plan is optimized to try and reduce drastic changes in angle, called DogLeg Severity or DLS, and to minimize the complexity of the well.
The directional plan also includes careful selection of the directional tools, mud motors, and the rotary steerable system that will be required in order to hit the directional targets in the best way possible. To help these tools guide the well path to the optimum position, careful selection of the drill bit is required to ensure that it is compatible with the tools, the formation being drilled, and the directional change requirement, or Build Up Rate (BUR).
By selecting a drill bit that achieves the best compatibility possible with the directional tools, the tool can better guide the well path to the optimum position for the formation being drilled and any directional change requirements or build up rates (BUR) that may be encountered.
Ulterra specializes in creating custom drill bit designs which are compatible with all aspects of the application and the directional drilling requirements. Our knowledge and expertise of directional drilling applications mean that we can offer bespoke solutions that convert to high rates of success in this high-cost environment, where success is the only option!