Horizontal Directional Drilling for Oil and Natural Gas
Table of Contents
1 Introduction: Horizontal Drilling
The process of horizontal drilling 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 20th 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 properties of formations and traps which contain these resources, horizontal directional drilling became a more appealing method of efficient and effective production.
Most oil wells before significant advances in horizontal drilling technology 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 impact on the environment.
If these benefits were not enough to underscore the remarkable advantages of horizontal directional drilling, the technological advancements and resulting shale boom must.
Developed with the technology of hydraulic fracturing, horizontal drilling acted as a catalytic element, rapidly pushing advancements forward 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 it’s a positive contribution toward global energy production.
2 Oil Exploration
The strong bond formed between hydrogen and carbon makes a plethora of naturally occurring molecular compounds highly useful in energy generation and material creation.
Synthetic materials and fuels responsible for technology and electricity are the backbones for the entirety of technological success, imminently increasing human longevity benefits and population flourishing of 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 with frequency around the world. Taking note of 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. Many of 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 the disadvantageous cost-benefit and negative productivity associated with them. The last few decades of experience and technology growth in producing unconventional resources has 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 as well as environmental concerns. Wells are typically drilled as exploratory or production wells, one meant for discovery and information, the other for significant resource production.
Once a site has been properly evaluated by geophysics teams 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. While the depth of the hole 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 reach the pre-set depth. As the hole depth increases, the casing is added for anti-contamination, well stability, and several benefits which mature later in the drilling operation. Once the intended depth is achieved, a host of 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 successfully deviate or horizontally drill a well.
The bottom hole assembly and weight on bit (WOB) were the initial parameters horizontal drilling techniques manipulated to accurately deviate a well. The placement of drilling stabilizers, as well as rotary speed, and size of stabilizer 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 between 50 to 90 feet up the drill string, and a final stabilizer 30 feet above that. 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 allow 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 purposes. Dogleg severity, complicated or unfamiliar geologic features, telemetry obtained while drilling, as well as employing proper drilling operations are important to identify and address carefully to deviate the well. Drilling operations employed in horizontal drilling include:
Geosteering: the use of measurement or logging-while-drilling (MWD or LWD respectively) data technologies 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 is returned to its vertical orientation.
Sidetracking: adding another path to the existing wellbore, accidentally, to explore a nearby geologic formation, for multilateral drilling operations or any 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
Depending on the location and geologic features, accessing one or several features may be necessary. Properly designing and planning a well is crucial to reaching multiple targets several kilometres underground. Instances, where a single target must be reached often, means reduced complexity, though there is no guarantee of this.
The aim of designing a well is to successfully extract target resources while keeping costs at a minimum. Typically designing a directional well takes place 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 creates the possibility of using this data to actively steer the direction of the well. 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 a wide variety of scenarios, efficiently solving the problem of producing resources from locations otherwise inaccessible. Geological, technical, topographical, and space-related issues are solved, albeit 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
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
7.1 Fault drilling
Hydrocarbons are found in a tremendous variety of 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, it is easier to deviate a well and drill horizontally to the formation. 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 in the modern world. Extended reach 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 simply the area near a Wellpath that produces hydrocarbon resources. Many of the formations that produce oil and natural gas run horizontally. Vertical wells are at a significant disadvantage when attempting to free 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 enterprises otherwise cost-prohibitive, such as those in the North Sea. Critically, this application of directional drilling 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 a vital process in recovering a damaged, blown out, or wild well. Directional drilling is one of the few methods for bringing these wells back under control or sealing them off. Starting with a new well, drillers employ horizontal drilling to intercept the damaged well. This relief well provides expert crews with the means 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 access to hydrocarbons.
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 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 and the wellbore deflection angle achieved, drilling holds at that angle. 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 the use of 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 to further production.
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. Additionally, this exceptional technology has 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 leading exporters of natural gas in an incredibly short period. As the expertise and technology for this method of production improve, so grows the opportunity for access to affordable and reliable energy around the world.
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