Horizontal Directional Drilling for Oil and Natural Gas

1 Introduction: Horizontal Drilling

The process of horizontal drilling of deviated wells has existed for the better part of a century in any widely acknowledged fashion. Disputes over oil well production at the turn of the 20^th century indicate early uses of this technique. Once established as a repeatable means of extracting resources (natural gas, oil, and water), the technology and methods to achieve a deviated well began improving.

Due to increased knowledge regarding the properties of formations and traps that contain these resources, horizontal directional drilling has become a more appealing method of efficient and effective production.

Before significant advances in horizontal drilling technology, most oil wells were a simpler, vertical variety. The benefits of directional drilling include much more than better access to resources. Horizontal drilling techniques allow for fewer drilling pads, pressure relief for out-of-control wells, versatile installations of underground utilities, and reduced environmental impact.

If these benefits were insufficient to underscore the remarkable advantages of horizontal directional drilling, the technological advancements and resulting shale boom must.

Developed with hydraulic fracturing technology, horizontal drilling acted as a catalytic element, rapidly pushing advancements in engineering, operations, and materials for oil and natural gas production. The worldwide economy-shifting tremors felt by the U.S. Shale Revolution have dramatically demonstrated its positive contribution to global energy production.

2 Oil Exploration

The strong bond between hydrogen and carbon makes many naturally occurring molecular compounds highly useful in generating energy and material.

Synthetic materials and fuels responsible for technology and electricity are the backbones of technological success, imminently increasing human longevity benefits and population flourishing over the last several centuries. Disciplines including geology, engineering, material sciences, and surveying technology proved instrumental in advancing oil exploration efforts to detect and model formations more effectively.

Exploration geophysics uses gravity, magnetic, and seismic surveys conducted with sophisticated technology to map features of sub-surface geography, where hydrocarbon seeps and pockmarks are not self-evident.

3 Horizontal Drilling: Formations

Natural gas and oil seeps occur naturally and frequently around the world. Noting these seeps is easy enough. Discovering formations thousands of meters beneath the Earth’s surface is more challenging.

Oil and natural gas fields, reservoirs, traps, and tight formations are all made more accessible through horizontal drilling processes. These formations are created by geological movements or structures such as faulting, folding, and pinching out. These formations are generally categorized as conventional or unconventional.

Conventional hydrocarbon resources can be accessed using vertical wells and relatively simple approaches. Should these conventional resources be located in high-pressure areas, a relief well can be horizontally drilled to mitigate the pressure or effectively terminate the original well.

Unconventional hydrocarbons have long been inaccessible to motivated producers due to their disadvantageous cost-benefit and negative productivity. However, the last few decades of experience and technological growth in producing unconventional resources have reversed this norm.

Many unconventional resources are located within horizontally oriented formations or seams. Tapping into these unconventional resources was only possible with horizontal drilling effectively paired with hydraulic fracturing techniques. The surfeit of abundant, inexpensive natural gas resulting from the U.S. shale boom and its tremendous impact on the world provides ample evidence for its effectiveness.

4 Well Drilling

Hydrocarbon well drilling is a well-honed, ever-advancing process that has admirably adapted to the latest technologies and environmental concerns. Wells are typically drilled as exploratory or production wells, one meant for discovery and information and the other for significant resource production.

Once geophysics teams have properly evaluated a site for production, roughnecks and other crew set up the equipment and rig necessary for a drilling operation.

Beginning with a starter hole, the crew drills to a predetermined depth above the oil trap or reservoir. They place the collar, drill bit, and drill pole in the surface hole, attaching the rotary Kelly bushing (Kelly) and turntable before they begin drilling. As the hole depth increases, crews stimulate mud into the pipe through the bit to remove rock debris from the hole.

New joints or pipe sections are added, deepening the surface hole to the pre-set depth. As the hole depth increases, the casing is added for anti-contamination, well stability, and other benefits that mature later in the drilling operation. Once the intended depth is achieved, important tests are run to gather relevant geological, surveying, and well-tracking data.

This data serves skilled crews in immediate operations and provides generous amounts of research data for experts and machine learning systems to process for further advancements in state-of-the-art methodology.

5 Horizontal Directional Drilling

Horizontal drilling shares many similarities with vertical drilling, though planning, techniques, and tools vary significantly. Principally, horizontal drilling begins with altering the good path at the kickoff point (KOP). The drill string and bottom-hole assembly (BHA) use several directional drilling operations to deviate or horizontally drill a well successfully.

The bottom hole assembly and weight on bit (WOB) were the initial parameters of horizontal drilling techniques manipulated to accurately deviate a well. The placement of drilling stabilizers, rotary speed, and stabilizer size greatly impact the accuracy of horizontal good trajectories.

Variances of stabilizer placement along the drill string produce building, dropping, or holding angles, allowing accurate adjustments to a well’s trajectory.

• BHA for Building Angles utilizes a full gauge stabilizer near the bit, a second stabilizer between 50 and 90 feet up the drill string, and a final stabilizer 30 feet above. This configuration creates a fulcrum, adding side force to the bit.
• BHA for Dropping Angles: uses the first stabilizer between 30 and 90 feet above the bit, creating a pendulum-like effect. This arrangement generates a negative side force on the bit, dropping the angle.
• BHA Holding Angles: uses up to 5 stabilizers in the BHA, placed roughly 30 feet apart to maintain downward driving force, avoiding both fulcrums and pendulums.

Varying the placement of collars (heavier drill string/column pieces) and stabilizers allows drillers to achieve remarkably consistent angular adjustments when drilling a horizontal well.

Despite these advancements in BHAs, many other considerations must be made for horizontal drilling. Dogleg severity, complicated or unfamiliar geologic features, telemetry obtained while drilling, and employing proper drilling operations are important to identify and address carefully to deviate the well. Drilling operations employed in horizontal drilling include:

• Geosteering: using measurement or logging-while-drilling (MWD or LWD, respectively) data technologies to gather information on the fly to increase well trajectory accuracy.
• Jetting: uses a special nozzled bit to pump fluids at high velocity into the drill path, deviating the well.
• Kicking-off: changing the direction of a Wellpath from one distinct trajectory to another.
• Nudging: a technique used to move a vertical well around a hazard. Once guided around the hazard, the well returns to its vertical orientation.
• Sidetracking: accidentally adding another path to the existing wellbore to explore a nearby geologic formation for multilateral drilling operations or other reasons.
• Whipstock: a down-hole deployable, wedge-like tool used to deflect the bit angle slightly for sidetracking or other operations.

6 Designing A Directional Well

Accessing one or several features may be necessary depending on the location and geologic features. Properly designing and planning a well is crucial to reaching multiple targets several kilometres underground. Instances where a single target must be reached often mean reduced complexity, though there is no guarantee.

Well design aims to successfully extract target resources while keeping costs at a minimum. Typically, a directional well is designed within sophisticated 3D modelling software, which allows for highly optimized well paths. Applying technological advancements such as 3D modelling with steering produces excellent results.

The rapidly improving ability to generate and collect data using MWD and LWD technology feeds into 3D imaging programs. As data is transferred into imaging programs and other software, it becomes possible to steer the well’s direction actively. This method of calculating well trajectory saves significant amounts of cost and time when drilling a horizontal well.

7 Applications for Directional Drilling

Horizontal directional drilling addresses various scenarios, efficiently solving the problem of producing resources from inaccessible locations. Geological, technical, topographical, and space-related issues are solved at an increased cost related to deviating a well—horizontally drilling—to reach a resource. Applications for horizontal directional drilling include:

• Fault drilling horizontal drains
• Inaccessible location
• Improved productivity by increasing the pay zone
• Multiple areas of sand from a single wellbore
• Multiple exploration wells from a single wellbore
• Offshore multiwell drilling
• Onshore multiwell drilling
• Relief well creation
• Salt dome drilling
• Sidetracking

7.1 Fault drilling

Hydrocarbons are found in various formations and geologic structures, including formations within fault planes. These fault planes are difficult to access using vertical wells. Rather than drilling through a steeply inclined fault plane, deviating a well and drilling horizontally to the formation is easier. Engaging hydrocarbons within fault planes can be difficult and even dangerous due to slippage with traditional means. Horizontal drilling mitigates the risk by avoiding drilling straight through fault planes.

7.2 Reaching inaccessible locations

Creating extended-reach, horizontally drilled wells is a common phenomenon today. These wells are drilled to access hydrocarbons from precarious, often inaccessible locations. Formations located beneath bodies of water, cities, mountains, or other geologic barriers are accessed by extending a horizontal well for many kilometres or miles as necessary.

7.3 Improving productivity by increasing the pay zone

The pay zone is the area near a Wellpath producing hydrocarbon resources. Many of the formations that produce oil and natural gas run horizontally. Vertical wells are significantly disadvantaged when freeing hydrocarbons from these formations and seams (pay zones). Horizontal, directionally drilled wells run parallel to the seams, covering significantly more area.

7.4 Multiple exploration wells

The single well path may be plugged at depth, allowing drillers to deviate the well towards a new direction. Drilling from above a plugged area allows further exploration without drilling full-length wells.

7.5 Onshore and offshore multiwell drilling

Multiwell drilling is an important aspect of both onshore and offshore drilling. Reliably deviating a Wellpath allows multiple wells to be drilled from a single, primary borehole. Multiwell horizontal drilling allows companies to take on otherwise cost-prohibitive enterprises, such as those in the North Sea. This directional drilling application critically reduces the necessary infrastructure and overall footprint of accessing hydrocarbon resources. As many as 60 wells can be drilled from a single origin point.

7.6 Relief well creation

Creating a relief well is vital in recovering a damaged, blown-out, or wild well. Directional drilling is one of the few methods to keep these wells under control or seal them off. Starting with a new well, drillers employ horizontal drilling to intercept the damaged well. This relief well allows expert crews to cut off, mitigate, or seal the uncontrollable well.

7.7 Salt dome drilling

Salt domes are a type of impermeable geologic formation which protrudes vertically through layers of strata. Due to the impermeability of these formations, the possibility of trapped hydrocarbons in their vicinity is increased. Salt domes present several difficulties and potential hazards when drilled directly through. Approaching these formations using horizontal drilling allows for safe, reliable hydrocarbon access.

7.8 Sidetracking

As the name implies, sidetracking is simply deviating a Wellpath. Sidetracking is typically done to avoid obstructions in the well or well path. Pieces of equipment, such as drill string sections, become stuck. Sidetracking or deviating from the good path is a viable, oft-employed solution to continuing around obstructions. Simple wellbore repositioning, avoiding lease lines, and maintaining well spacing requirements are all reasons for using sidetracking techniques.

8 Types of Directional Wells

There are three primary wellbore profiles: build and hold (standard), build-hold and drop (S well), and continuous build (J well). These Wellpath trajectories are often altered slightly by geologic circumstances on location.

8.1 Build and hold

The most common type of horizontal well is the simplest in design and execution. The kickoff point for build-and-hold wells is relatively shallow or moderate in depth. Once the KOP is reached, drilling holes at that angle and the wellbore deflection angle is achieved. While holding at that angle, drilling proceeds until the identified hydrocarbons are reached.

8.2 Build-Hold and drop

Completion requirements for reservoirs may require a build-hold and drop configuration. Composed of three straight, one build-up, and one drop-off point, ‘S type’ wells begin their wellbore deflection early on. Once the appropriate level is reached, the Wellpath is returned to near-vertical orientation before drilling to the target area.

8.3 Continuous build

Continuous build or J-type wells have the deepest KOP out of the primary well profiles. This well configuration is used for exploration or gaining geological data, though they are found in more developed oilfields for further production.

9 Summary

Horizontal directional drilling has profoundly improved energy generation by providing safer and more effective access to hydrocarbon fuels. The central techniques of horizontal drilling are continually improved to achieve better results at less cost. This exceptional technology has also reduced the surface footprint of oil exploration and drilling. The surge of natural gas and oil following the U.S. Shale Revolution has exceptionally positive results, allowing the U.S. to become a leading natural gas exporter in an incredibly short period. As the expertise and technology for this production method improve, so does the opportunity for access to affordable and reliable energy worldwide.