High-tech, adaptive, and efficient, the oil and gas industry constantly seeks to improve all aspects of the value chain. Whether up, mid, or downstream processes, all undergo continual refinement. Upstream production is perhaps the first to explore and pioneer developing technologies. Sites located onshore and offshore increasingly use smarter, cost-cutting engines and fuel sources that are resistant to price fluctuations. Bifuel and dedicated natural gas engines are regularly employed in exploration and production efforts throughout the energy industry.
Often the choice to use field gas, pipeline gas, compressed natural gas (CNG) or liquefied natural gas (LNG) hinged on logistics related to distance and transportation. An agile natural gas industry, growing infrastructure, and the rapidly expanding availability of inexpensive hydrocarbon gases have virtually eliminated the downsides of drilling rigs fueled partially or entirely by natural gas. LNG fueled drilling rigs are now a timely turnkey solution for producers around the globe. Below we explore the critical aspects of upstream production and the vital components of drilling rigs that make it all possible.
1 Upstream exploration and development
At the root of most modern processes is knowledge. Oil and natural gas exploration relies on the most advanced information models used by geologists and other scientists. Geographic information software (GIS) may be used to model vast amounts of information. Biology, chemistry, and physics are key disciplines used with geology for resource exploration. Possible locations for hydrocarbon deposits, reservoirs, or other geologic formations are found through applying one or several advanced methods. Once determined as a possible site for oil and natural gas development, teams must address property and mineral rights, and subsequently begin exploratory measuring, scanning, and drilling operations. This early part of hydrocarbon production lays the foundation for choosing appropriate drilling rigs, engines, and fuels.
Scientists begin exploration at the highest level of conceptualization. This helps eliminate areas of that contain hydrocarbons at concentrations below commercial value. Extracting resources from these locations would prove too expensive with current technologies. Formations which trap hydrocarbons are well understood by scientists. Using geologic modeling exploration teams may narrow down reservoir locations without leaving their laboratories. This ‘type’ of exploration has been employed since the early days of oil exploration. Today’s geologists have built on these early concepts and ideas. Incorporating biology aids in determining what varieties of plant and animal life resided within a given area. Knowing this allows exploration teams to anticipate where hydrocarbons reside within a specific geography, including subsea environments.
Applying geophysics disciplines to exploration is also standard practice. Among these disciplines are geodesy, gravity, hydrology, magnetism, meteorology, oceanography, radioactivity, seismology, and volcanology. Seismology is perhaps the most used of these. This discipline studies the propagation of waves as they travel through layers of earth. Exploration teams employ a variety of seismic programs. Dynamite, vibration pads, or other sources are used to generate seismic waves. These waves travel through some layers and formations while bouncing off of others. Measurements of speed and reflection are taken. That data is analyzed to map the subsurface.
Once a reservoir is located, mineral rights and leases must be sought. The initial aim of exploration efforts at this stage is to drill a test well. Before drilling a test well, it is necessary to consider the surrounding lands, should the well produce. Additional wells would likely follow. If a company does not take the initiative to lease not only mineral rights, but the necessary surface land leases, another company would be able to drill the adjoining land. Ideally, landsmen responsible for arranging these rights would tie up all of the land covered by the exploration team’s prospect.
Surface rights on a site are secured before drilling licenses are applied for. Depending on the needs of the surface site, the surface lease could be less than 1 hectare (2.5 acres). Larger sized surface leases are required for roadways, easements, and sometimes to tie in the well to pipeline systems. For multi-well sites that employ horizontal directional drilling it is common for surface leases to exceed 6 hectares (15 acres).
Multiple wells drilled in this fashion significantly reduce the required operating space. As a result, environmental impact is reduced. Impact assessments and public consultations are frequently a part of this process. These assessments include archaeological, environmental, wildlife, and other assessments. Once concluded, the complex process of drilling and completing a well begins, generally with choosing the site requirements, rigs, power sources, and other vital components of hydrocarbon production. Though similar in many respects, onshore and offshore production sites have many differing requirements.
2 Offshore platforms
The earliest of offshore platforms were built in the 1890s, just before the turn of the 20th century. Initially they were little more than piers extending from onshore well pads. The first steel-pier island was an early forerunner of today’s highly sophisticated offshore platforms. Built ½ mile offshore with a 25-ft air gap, this steel island suffered from poor well production. 8 years after its initial construction, the prototype offshore platform was destroyed in 1940 by a storm. While early pier-platforms were built off of the California coast, on-water drilling took place in the swamps of Louisiana.
Rectangular, shallow-draft barges were constructed for this purpose. Tugs pulled them into place, where they were often submerged. Submerged barges were outfitted with lattice steel structures, allowing later barges to post in deeper waters. Often, pilings were used to prevent drift or movement due to waves and wind. By 1947 the first offshore tender assist drilling (TAD) unit was mobilized out of sight from land, around a 6-meter depth, in the Gulf of Mexico. It was equipped with the necessary drilling equipment set that typifies drilling rigs.
As companies progressed into deeper waters, platform designs and capabilities took off. Dozens of jacketed, submersible, moored tension leg, and floating designs flourished. By 1978 jacketed-support platforms were installed at nearly 400-meter depths. Typically, floating designs, submersibles, and semi-submersibles are used for deep waters. Some offshore platforms are designed to reach reservoirs several thousand meters below the surface. These long wells may be drilled from drillship, fixed jacket, or templates installed on the seabed.
All offshore platforms require the equipment necessary to process and safely handle the conditions of hydrocarbons produced from these reservoirs. Deep water platforms will contain quarters, recreation, and other facilities for the operators. At moderate depths it is typical to construct a variety of platforms to accommodate the crew or serve other necessities. It is possible for an offshore complex to have platforms for production, living, riser, satellite, wellhead, and flaring purposes. These platforms are connected by bridges, subsea cables, and infield pipelines. Depending on the platform’s location, it may be connected to an onshore processing unit.
3 Drilling rigs
Among the most iconic of sights associated with oil production is that of the drilling rig, usually the derrick at the center of a well pad or the unmistakable form of an offshore drilling platform. Drilling rigs are always designed for either onshore or offshore applications.
Custom designed for a wide variety of needs; onshore drilling rigs come in a variety of sizes. They may be portable, small, medium, or large sized. Some drilling rigs are customized for mining or other industries. Classifications for onshore drilling rigs include the categories of height, drilling method, derrick position, pipe used, power used, and directional drilling. Perhaps counter intuitive, drilling rigs have an extensive history of use.
Long before modern, engine-powered rigs were developed, pioneering Chinese developed the earliest known forms of drilling rigs to extract natural gas. As early as 500 B.C. Han Dynasty China used rotary and percussion drilling with iron bits to produce oil and natural gas. Derricks were constructed from bamboo poles while bamboo fibers provided a capable drill string. These early drilling rigs were initially capable of reaching depths of ten meters.
As improvements were made, bamboo drilling rigs in China reached depths of 100 meters. Later versions were capable of reaching nearly 700 meters. Drilling rigs made throughout these periods were man-powered using levers and teams of men. 16th Century Chinese drilling rigs would first be succeeded in technological development by 19th century rigs which used steam engines as their primary power source. Drilling rig derricks were primarily made of wood, while percussive drilling with cables was the norm. Cable tools were quickly replaced with rotary drill bits, providing exceptionally faster drilling times as well as the capability to reach greater depths.
At the turn of the 20th century the U.S. oil boom began with a blowout in Beaumont, Texas. Hundreds of feet of oil soared skyward. Rotary bits, drilling mud, and steam-powered rigs were assembled in a frenzy. More than 1,500 companies were created as tens of thousands of Americans flooded into town. Oil was in. A new era of energy production was underway from 1901. World War I only increased the demand for this reliable energy source. This flood of producers and workers generated a tremendous variety of improvements to drilling rigs and the practice of hydrocarbon production. From 1900–1950 the blowout preventer (BOP), steel derricks, drill bit advancements, offshore drilling rigs, and early horizontal drilling techniques were created. Hosts of improvements in efficiency, effective productive, and safety arose simultaneously. The second half of the 20th century only furthered the fantastic strides in technology and techniques used for hydrocarbon exploration and production.
Drilling rigs traded their steam-powered operations for combustion engines in the 1950s. By the 1970s, these engines powered multiple on-site generators. Bottom-hole assemblies, or drill bits, became more advanced. Operators gained the ability to steer drilling systems with greater accuracy. Tracking downhole drilling operations became more sophisticated with measuring and telemetry equipment. These improvements were pioneered to allow production teams to reach previously inaccessible reservoirs while increasing production rates. Paired with techniques such as hydraulic fracturing or other methods of well stimulation would eventually lead to precise, reliable horizonal directional drilling technologies in the early 21st century.
Within the last two decades oil and natural gas producers have combined advancing technologies from far flung disciplines to create highly efficient, effective, and safe drilling systems. The modern drilling rig is a custom engineered masterpiece of design. These drilling rigs are at the core of today’s global energy renaissance, the U.S. Shale Revolution.
One effectively designed drilling rig is capable of drilling multiple wells from a single well pad. Drilling is easily planned, controlled, and monitored using computer software, while operated from climate-controlled environments. Many drilling rigs are equipped with hydraulic ‘legs’ which allow the rig to ‘walk’ across a well pad to a new well site. It is difficult to overstate the impact of these massive and rapid advancements in drilling rig technologies.
3.2 Drilling rig classifications
Because a large variety of drilling rigs exist to serve a broad range of scenarios, many delineations exist for describing them. Exploration teams, well pad engineers, operators, and other experts require these classifications to choose the proper drilling rig for a given production goal. Drilling rigs may be designed for use with a singular drilling technology or with the ability to change and combine technologies to achieve their ends. Classifications based on height, derrick position, directional or horizontal drilling, mobility, drilling methods, drill pipe, ultimate drilled depth, or by power type are common.
Single — holds single drill pipes, may or may not have pipe racking fingers
Double — holds two connected drill pipes
Triple — holds three connected drill pipes
Quadri — holds four connected drill pipes
Conventional — vertical support structure dating back to archaic drilling operations
Slanted — slanted support structure often angled at 45 degrees for horizontal drilling operations
Conventional — derrick is mounted to a support structure, must be assemble and disassembled conventionally
Mobile — designed for mounting on vehicles and in some instances for transport via helicopter to some locations
Walking — derrick is capable of being mounted and is equipped with hydraulic ‘legs’ to allow movement from one well site to another at the well pad
Non-rotating — used on direct push rigs and service rigs (cable drilling)
Rotary — rotates the drill pipe by turning a Kelly bushing, a square or hexagonal pipe, in the rotary table
Top drive — rotates the drill pipe from the top off the drill string using a motor that moves on a track in line with the derrick
Sonic — advances drilling string with vibrational energy
Hammer — method using both percussive and rotational forces to drill, often down hole
Cable — braided or wired rope used to raise and drop the drill bit
Conventional — drill pipe made of metal or plastic materials
Coil tubing — flexible tubing of predetermined length with a downhole drilling motor, stored on a drum
Chain — chain used to raise and drop the drill bit, often with hydraulic rigs
Mechanical — has clutches, torque converters, and transmissions powered directly by engines
Electric — machinery driven by electric motors, powered by on-site engines
Hydraulic — utilizes hydraulic power to drive machinery
Pneumatic — uses pressurized air to power the rig
Steam — uses steam-powered engines and pumps to power rig (archaic)
3.3 Onshore drilling rigs
As the prototypical drilling rig, onshore rigs may appear simplistic in comparison to their offshore counterparts. While offshore drilling rigs share many similarities to onshore rigs, there are key differences. Onshore drilling rigs are by definition land based. They are capable of drilling shallow, deep, extended reach, vertical, and deviated wells. Ground transportation is most often required to move these rigs to their destinations. Reliability and ease of handling is highly prized with onshore drilling rigs. As operating rates are expensive, the ability to quickly move, rig up, and rig down is essential. More often than not the physical location and required drilling depth impact the size and chosen drilling equipment for land-based drilling rigs.
Land-based rigs are typically separated into the classifications of conventional or mobile. Conventional drilling rigs are equipped with load-bearing derricks, which are designed to remain anchored to the corners of a substructure throughout drilling operations. These rigs are generally larger in size, designed to house drill pipe sections of a greater length than exploration or finishing rigs. Land-based rigs of conventional design, despite the implication of their name, may be equipped with hydraulic legs. So equipped, they can move around a well pad with little assistance.
Onshore rigs may also be classified as mobile when mounted to wheeled trucks or readily transported by truck in a modular form. Mounted in this fashion, mobile rigs may be further classified by the type of mast, whether cantilevered, bootstrap, telescopic, folding, or otherwise.
3.4 Offshore drilling rigs
Platforms or vessels that function offshore are an iconic sight, inseparable from association with oil and natural gas. Partly because of their size and location, these drilling rigs are sometimes viewed with a sense of arcane wonder. The myriad of complex operations required to construct, transport, and anchor them would be enough to deter most casual onlookers from investigating them. In addition to these operations, offshore drilling platforms are increasingly capable of carrying out upstream processes within the oil and gas value chain. Offshore platforms can explore, drill, and extract hydrocarbons. Many offshore rigs process, store, and transport these resources as well. Finally, these marvels of modern engineering must accommodate the crews that carry out work on them.
Offshore drilling rigs are designed in dozens of ways. Ultimately their design is dependent on the environment they operate within. If operating within lakes, inshore waters, or inland seas, offshore platforms may be fixed to the ocean floor. Platforms that operate further offshore or in deep waters are more likely to consist of an artificial island, be partially or completely submersible, or take the form of a marine vessel.
Engineering for and operating in oceanic environments has long presented some of the most challenging conditions for human endeavors. Producing and transporting hydrocarbon resources from beneath the ocean floor certainly qualifies as challenging situation. It is among the most challenging and expensive undertaken in history. Only exceptional design, planning, management, and execution make these operations possible. Even then, the margins for error are virtually non-existent. Choosing the proper solutions at every point is essential to the success of offshore platforms. Accordingly, it should come as no surprise that offshore drilling rigs are among the most complex projects undertaken anywhere on earth.
Adhering to proper design principles and equipment selection is a fundamental consideration. Many of these aspects are tied directly to the operating conditions of an oil rig. Variability in the design and operation of an oil rig extends beyond its immediate operating conditions. Many operational aspects of drilling platforms contain flexible options. The configuration of platform complexes varies considerably from rig to rig, even when operating at similar depths. Subsea systems may be configured on the ocean floor. Additionally, many of the standard drilling rig components (discussed in further detail below) can be selected from dozens of options.
3.5 Horizontal directional drilling
Perhaps the most catalytic development of the last century within the oil and natural gas industry is the perfection of horizontal drilling techniques. Horizontal drilling was first pioneered in an experimental fashion in the early 20th century. Companies as early as the 1920s took note of oil wells that dropped significantly in production and pressure amounts. Though incapable of proving such at the time, some suspected rival companies of drilling horizontally into their reservoirs. Officially, horizontal directional drilling (HDD) became a recognized possibility in legal disputes between production companies.
Originally this technique was considered outright impossible or highly improbable at the least. Horizontal drilling was confined to the category of phantom phenomena until early, niche-practice pioneers in the 1930s demonstrated their ability to drill directional wells. Many decades would pass before HDD became a truly significant source of investment for drilling and production companies. This was largely due to the limitations of technology, materials, and engineering. Many difficulties prevented the regular use of HDD oil wells.
Initially, HDD techniques were employed to deviate a well for simple, functional reasons. Operators during these times would sometimes deviate or dogleg a well to avoid an obstruction. Whether encountering an unexpected geologic formation or avoiding trapped equipment, very few operators could accomplish this demanding feat. The next developments in horizontal drilling took place in the 1970s with the advent of downhole drilling motors. Combining this technology with adequate telemetry systems allowed operators to effectively and reliably steer the direction of a wellbore, regardless of its depth.
Horizontal wells provide several distinct advantages over conventional horizontal wells. Early horizontal wells were used to relieve well pressure in out of control (blowout) oil fields. Modern horizontal wells are drilled to reach locations inaccessible to vertical wells, typically those underneath cities, lakes, or preventative geologic formations. The dimensions of horizontal wells also provide significant benefits to producers. Multiple wells may be drilled from a single, initial well.
Drilling multiple wells from a single well produces a cascade effect in both onshore and offshore drilling environments. Onshore, it significantly reduces the footprint of a well pad. This impacts everything from mineral rights and land leasing to dozens of operational concerns. Only a single wellhead is needed to maintain production of multiple wellpaths. Offshore drilling platforms are dramatically impacted by this practice. As many as 40 well paths may be drilled from offshore platforms using horizontal drilling techniques. The net result is much more efficient, less costly, and safer production of oil and natural gas. Combining horizontal drilling with hydraulic fracturing may be the crowning achievement so far in HDD operations.
Unconventional resources, previously inaccessible, are now developed on large scale. Without HDD this would be impossible. The majority of unconventional resources present themselves in horizontal geologic formations. Horizontal drilling alone would not be enough to stimulate commercial production of oil and natural gas from these formations. Recently pioneered, hydraulic fracturing is a well stimulation technique used to produce unconventional resources. High-pressure fracturing fluid is injected through perforations in specially designed, horizontally drilled well casing. Fracturing fluids containing sediments or nanoengineered proppants induce desired flow rates. The combination of these technologies created a renaissance in the energy industry known as the U.S. Shale Revolution. Abundant and reliable natural gas production has skyrocketed to levels previously unimaginable.
3.6 Drilling rig components
At a minimum, all drilling rigs require a handful of principal components. The components include a mast (derrick), blowout preventers (BOP), drawworks, drillstring, engines, and a mud system.
The mast is the support structure, erected above the well, which allows operators to add and remove drill pipe or equipment into the well. Blowout preventers are a type of valve used to reduce and control erratic or unexpected pressures while the drawworks are comprised of hoisting equipment for the rig. An oil drilling rig’s rotating assembly is referred to as the drillstring. The rotating Kelly, drill collars, bit, and pipe comprise the drillstring. Power is delivered to all primary and subsystems of the site through the drilling rig engines. Mud systems employ pumps, tanks, a circulating hose, and flow lines.
When considered as systems, these components are grouped into five distinct systems:
Circulating system — mud pits or tanks, pumps, lines, hoses, mixing hopper, standpipe, and shale shakers
Hoisting system — includes derrick, crown block, drill line, travel block and tackle, and drawworks (mechanical winch)
Power system — uses engines, electrical generators, and drilling rig fuel
Rotary system — includes the Kelly or top drive system, rotary table, drill bit, and swivel
Well control system — BOP, bell nipple, rams, choke or kill lines
4 Drilling rig engines
Excepting the early usage of steam-powered engines, diesel engines have long been the engine of choice for powering drilling rigs. Sturdiness, reliability, and efficiency are synonymous with diesel engines. Located onsite at well pads and platforms, they typically range from 400 – 3,000 hp. As the sole source of power generation at many production sites, these engines are essential to all drilling operations. Renowned for their steadfast performance, diesel engines maintain their status as the dependable internal combustion engine for drilling rigs.
Though standard diesel engines operate on diesel fuel, modern variants patented as early as 2001 may use several fuel types. Continual refinement of blending kits and engine design has produced highly efficient dual-fuel and dedicated natural gas fueled engines for drilling rigs. The first drilling operations to utilize prototype natural gas engines produced exciting results. Offshore rigs operating with these prototype natural gas fueled diesel engines demonstrated savings in excess of 4,000 USD per day. Current dual-fuel natural gas (diesel displacement or bifuel) and dedicated gas diesel engines outstrip those figures. Benefits relating to operational efficiency were accompanied by a reduction of harmful emissions.
In the wake of early, successful experimentation with natural gas fueled drilling engines, spark-ignited (SI) and turbine engines are now capable of duel-fuel and dedicated gas operation. Though not as widely used as diesel engines for drilling operations, each engine presents advantages and disadvantages for rigs.
SI engines are adequately used to sustain stead loads, typically for electric power generation. Conventional or dual-fuel diesel engines are used to aid SI engines by supplying high transient load response for some drilling operations.
Turbine engines are used for a variety of purposes on drilling rigs. Large turbine engines can be used for both stationary and mobile electric power generation. Smaller turbine engines are frequently used to power hydraulic fracturing pumps. As these engines are highly configurable, they are well suited to use a wide variety of combustible fuels. Turbine engines are capable of dedicated natural gas configurations.
Drilling rig engine configurations include:
Diesel – conventional, dual fuel, and dedicated gas
Spark-ignited – dedicated gas
Turbine – dedicated gas
5 Engine fuels
As the exploration and production of natural gas resources has increased, the idea of fueling drilling rigs with field gas, CNG, or LNG has grown in prominence and viability. Diesel fuel remains the dominant energy source for drilling rig engines. Yet the data indicates significant cost benefits and emission reductions for adopters of natural gas fueled drilling engines. Following initial success and growing adoptions of natural gas fuel sources, many pioneering companies have emerged to provide LNG to onshore and offshore drilling operations.
5.1 Diesel fueled drilling rigs
Fueling drilling rig engines with diesel fuel is the conventional way, with sound reason. The diesel engine was designed to operate at peak output and efficiency with it. As the standby fuel for generations, systems and processes to transport, store, and use diesel are well established. Marginally, diesel outperforms levels of energy production that dual-fuel retrofits. Despite the obvious benefits of diesel fuel, there are significant upsides for operators that adopt natural gas fueled drilling rigs.
5.2 Natural gas fueled drilling rigs
Drilling rig engines fueled with natural gas stand to gain economically and environmentally, though initial adoption can prove costly for some. Natural gas can be supplied as an alternative to diesel in four forms. Field gas, pipeline gas, compressed natural gas, (CNG) or liquefied natural gas (LNG). Generally, transportation and availability play primary roles in deciding which natural gas fuel is the best option for fueling drilling rigs.
LNG is primarily liquefied methane gas, cryogenically cooled to -260 degrees Fahrenheit. Both transportation and storage of LNG fuel is conducted at near atmospheric pressures. Vaporization is required on-site for use in LNG fueled drilling rigs. By contrast, CNG is stored and transported under high pressures in cylindrical pressure vessels. When transportation distances are relatively short, CNG fueled drilling rigs are viable. Modular LNG and CNG facilities are rapidly emerging to provide these services, sometimes referred to as small-scale LNG facilities. Pipeline quality natural gas is a highly desirable fuel source for drilling rigs where available.
Field gas is another greatly appealing form of natural gas fueled drilling rigs. This ‘wellhead gas’ is locally sourced, has the smallest carbon footprint and the highest reduction in operating costs of all available fuel sources (as much as or exceeding 90% reduction of fuel cost). The composition and quality of field gas may vary greatly from one site to another. Some processing is necessary to fuel drilling rig engines with field gas.
The bottom line for natural gas fueled rigs is that they reduce operating costs while generating fewer emissions. In particular, reduction of nitrogen oxides and particulate matter.
5.3 LNG fueled drilling rigs
Pioneered in Texas nearly a decade ago, highly portable and efficient LNG fueling systems for drilling rigs has reached a mature level of development. Turnkey services for fueling, regasification, and storage are readily available for operators. Boasting 50% or more cost reduction that diesel fueled rigs is difficult to turn down for many companies. Permanent LNG systems have smaller footprints than their conventional equivalents and conversions for equipment are relatively simple. The safety record of LNG, a colorless, odorless, non-corrosive, and non-toxic fuel is without peer. Increases of infrastructure and transportation continue to make LNG fueled drilling rigs more accessible to upstream producers.
As a liquefied form of natural gas, LNG rests at 1/600th of its original volume. Energy dense and easily stored or transported whether on the grid or remotely located. Mobile storage and skid mounted, or mobile vaporizers, are simply prepared and brought onsite. Additionally, the price of LNG is remarkably stable in contrast to that of diesel fuel. Average adopters of LNG fueled drilling engines will spend less than half as much per day on fuel.
Engine fuels, engines, and drilling rigs themselves are at the fore of producing the world’s energy supply through highly planned, complex projects which aim to operate as efficiently and effectively as they are able. Thorough exploration reveals the precise requirements for a site, whether onshore or offshore. Regardless of location, drilling rigs and their components are continually improving in design and operating practices.
Often these operations are technology heavy and pioneering in nature, constantly seeking to push the envelope of their exceptional capabilities further. Developing engines fueled by natural gas is the next logical step towards improving these goals. LNG fueled drilling rigs, in particular, offer increasingly significant advantages as global infrastructure for LNG becomes more plentiful, agile, and inexpensive. Continual discoveries of vast natural gas fields and the growing ability to economically produce unconventional resources all but ensures LNG as the emerging, dominant choice for fueling production operations well into the future.