Table of Contents
1 Introduction to Drilling, Dewatering, and Geosteering
Whether remote taiga, barren desert, on the high-elevation mountainside, or deep ocean, the most impressive and difficult production projects undertaken in today’s industries are those which take place in remote environments. These projects often require the skills of dozens of teams who draw materials and expertise from around the world. One team or technology out of place during this process can throw the entire symphony into disarray, potentially increasing the cost of capital projects by millions of dollars, delaying project completion, or precipitating critical failure.
Today’s complex operations could not be accomplished without the expert coordination of these teams combined with remarkable technologies which increase the effectiveness and efficiency of these operations at bounding rates. Remote drilling operations have long been carried out at phenomenal risk and expense to companies involved. Present-day operations mitigate many of the risks inherent in these projects through several means, including new materials, advanced technologies, and improved project management processes.
Remote drilling and dewatering efforts are increasingly attractive solutions for several industries, mining, perhaps, chief among them. It is an incredible feat of modern engineering to meet the needs of projects which require high-tech drilling rigs in difficult to access environments. Secured on-site, these portable drilling rigs use advanced Geosteering techniques to remove water from the project site, often a construction site or mine shaft.
2 Remote Location Drilling
Drilling operations often take place in environments that have at least minor infrastructural development. However, exploration efforts around the globe have uncovered vast deposits of oil and natural gas in remote, usually challenging, environments. Producing natural resources from these locations has long remained a prohibitively expensive possibility. Today’s technology provides dozens of solutions to the problems faced by producers in the mining and energy sectors. When properly designed and deployed, modern drilling rigs, measurement technologies, and drilling techniques allow for the exploration and production of minerals and other valuable resources. Harsh environments that require unique drilling rigs include:
- The Arctic and extreme cold — Alaska, Canada, Russia
- Deserts — Africa, Australia, Middle East
- Jungles — Papua New Guinea, South America
- Offshore — Platforms in Canada, the North Sea, Russia
- Mountains —Central and South America, Kurdistan
Innovations within the drilling and exploration disciplines have brought these remote locations from the frontier closer to the mainstream. Previously, resources in remote environments were largely inaccessible, even if their presence could be accurately determined. Early mobile drilling platforms paved the way to exploration in harsh environments. These operations were often inefficient. The risk involved in undertaking a remote exploration or drilling project was dramatically increased when compared to typical projects.
The earliest remote location operations sometimes saw entire projects abandoned for a near-total loss. When the disaster was warded off, early projects such as these were costly and inefficient, supplying fuel to continue operations could single-handedly create a net loss for a project. Subsequent decades resolved many of these issues.
Today’s exploration and drilling techniques effectively allow producers to discover and access vast amounts of higher quality resources in a safer, more effective manner. Once discovered, the application of advanced drilling and well construction methods develop wells which produce significantly greater quantities of oil and natural gas with less risk to both crew and environment.
2.1 Technologies required for remote location drilling
Today’s remote location exploration and drilling projects benefit from an array of technologies. The overall effect of these benefits allows producers to tap into vast reserves of high-quality minerals and energy resources.
Drilling in remote locations provides several key challenges to expert teams of explorers and producers. It is the mastery of these challenges which makes remote location drilling possible. Several critical developments that make drilling in remote locations viable include:
- More accurate and efficient exploration technologies
- Custom engineered drilling rigs
- Horizontal drilling and hydraulic fracturing
- Increased accuracy and precision of well paths
- Less crew required for drilling operations
- Advanced guidance software and data analytics
- Less risk at drilling sites
- Smaller well pad footprint
- Highly developed procurement and construction industries
- CNG and LNG fueled drilling sites
A host of vital improvements have led to the economic development of resources which would have been far too costly in the recent past to produce. Once reservoirs or gas fields are located and mineral rights acquired, well pads are constructed. These drilling sites are considerably more feasible for remote location drilling. Multiple well paths can easily be drilled from a single wellhead and drilling rigs can be relocated around the well pad with remarkable ease.
Today’s well pads require fewer crew members to operate effectively and make use of advanced models which track the wellbore in real-time. Drilling adjustments are made by a single operator with a screen and joystick. Adding and removing drill strings can be entirely automated. Multiple targets, several kilometres below the surface can be accessed along a single Wellpath, furthering the economic efficiency of drilling sites.=
Along with these technological improvements are those related to fueling on-site operations with highly efficient and much cleaner natural gas. High-horsepower diesel engines are frequently fitted with bi-fuel systems, while dedicated natural gas engines see increasing use. Drilling rigs are routinely fueled by field gas, pipeline quality gas, CNG, or LNG.
Modular systems for transport and vaporization are matured in development and widely available. These fuel systems massively reduce emissions and provide significant cost reduction for drilling rigs. The rapidly improving availability of these fueling solutions only increases producers’ ability to drill in remote environments as though connected to large, efficient infrastructures.
Resources accessed by drilling are sometimes found with liquids that can damage equipment, increase on-site risk, and prevent teams from reaching project production goals. Dewatering is the process which removes liquids from these environments. Commercial dewatering requires expertise in designing, installing, and maintaining water control systems. Dewatering efforts must be tailored to the individual project requirements if they are to remain cost-effective and prevent budget changes or schedule delays. Dewatering often takes the following forms:
- Deep wells
- Horizontal dewatering
- Pressure relief wells
- Well points
Groundwater control and high-wall stability are among the most prominent uses for dewatering operations. Dewatering is particularly critical to the planning and development of mining operations. Compliance with local and international laws often dictate some dewatering requirements for mines. Safety requirements for mining crews mandate reliable, effective dewatering or water control systems completed with ISO or high standards of certification.
Large, open-pit, mines may run into groundwater as the mine grows in size and depth. The inflow of these waters holds the potential to disrupt mining operations. Typically, this takes the form of delaying production and damaging overall project production goals. Wet mining, enduring this groundwater inflow, can easily cost tens of millions of dollars in a single year. Avoiding the delay in production is important yet risks to onsite crew and equipment persist if dewatering remains unaddressed.
Continuous mining operations may require large diameter wells to pump water out of mine pits. Large diameter wellbore is often highly technical. Various ground conditions, lower water tables, fractures, and other considerations must be accounted for. Large diameter wells can be significantly more difficult to achieve in remote drilling environments. Accounting for the difficulties, this type of dewatering is necessary for many projects to maintain production goals.
Custom designed drilling rigs are frequently used in such circumstances. This aspect of drilling and dewatering is critical to most operations. Drilling rigs represent one of the most significant costs in mining or oil and natural gas development. Budget often determines the available rigs, followed by rig depth rating and operating parameters. With the right expertise and rig selection, drilling large diameter wells for dewatering becomes an option for water control.
3.1 Dewatering methods
Water control methods are selected and designed on a case by case basis. Site requirements and budget generally dictate the most effective method for controlling water tables. Construction projects, mining operations, aquifer testing, and many other environments create unique constraints for designers to consider. Each of the following methods provides dewatering and may be used in conjunction to continually serve that end.
3.1.1 Deep Wells
Deep wells are most commonly used in excavations where drawdown is required below 6 meters and soil permeability is moderate or high. Certain conditions may call for the installation of deep wells to underdrain less permeable strata.
Multiple deep wells are usually installed in an array, internally or externally controlling groundwater. These arrays pair with physical cut-off walls such as a diaphragm wall, secant-pile, or sheet-pile. Deep wells consist of a borehole, slotted screen, an annular filter pack through the stratum. A submersible electric pump is installed near the base of the well within the liner. The pump is connected via the riser pipe to the surface. Water is then pumped into a header main before it is discharged or recharged.
A hydraulic gradient is formed as water is pumped from the deep well, resulting in a cone of depression forming around the well. Little to no water remains within the pore spaces in the surrounding soil. Drilling deep wells are accomplished using either cable or rotary methods, most often resulting in a 250-300mm bore. Some ground such as chalk or sandstone may utilize wells that feature an open-hole section.
Where soil permeability is low the deep well may be sealed and a vacuum applied to increase well yield. This method can dramatically improve product rates for deep wells. Depths exceeding 40m are much more efficient when using vacuums than ejectors. Deep wells may be created to recharge water back into the ground using recharge or reinjection wells. These wells are similar in overall design to a deep well but serve the narrow purpose of recharging water into a different stratum.
3.1.2 Ejector Wells
Low permeability soils such as fine sand or silt are best dewatered using ejectors. Ejector wells are most common up to depths of 40m, where vacuum deep wells perform more efficiently. Occupying a unique position in the dewatering toolkit, ejectors operate where pumping levels are deeper than suitable for well points and where well yields are too minimal to justify using submersible electric pumps.
Ejector wells are drilled and installed like deep wells yet differ in the extraction method. Ejectors are designed to pump water and air mixtures without issue. Submersible pumps attempting to pump water and air mixtures can easily burn out. Sealing the borehole on an ejector well creates a vacuum during the pumping action, which in turn improves gravity drainage towards the well.
These well systems use both a high-pressure supply and low-pressure return header main which follows the line of wells. Site conditions may require a concentric or double pipe ejector system to provide the optimal solution. Ejector wells typically require a more experienced crew to operate than deep well or wellpoint systems. They may also require more regular maintenance than other water control systems.
3.1.3 Horizontal Dewatering
Projects that benefit from relatively shallow, linear configurations such as railways or long and narrow excavations are more likely to use horizontal dewatering methods. Typically, drainage lines are 80 to 100mm in diameter and up to 6 meters in depth, depending on what the site requires. Drainage trenches are excavated using a specialized trenching machine which uses rotary cutting chains to create trenches of appropriate depth and width.
Drainage lines are installed along the bottom of the trench as it is excavated. Once installed, the trenches are backfilled. Aquifers on site with low permeability can use filter gravel for backfill in place of soil to increase drainage capacity. The installed drainage lines are connected to a vacuum piston pump. The pump creates a negative pressure gradient which is necessary for water transfer. Collected groundwater is transported through the pump to an outlet line. Water is further routed to the designated discharge point.
Horizontal dewatering is often less expensive than other means, as less crew are required to install this water control system. Horizontal dewatering systems may be used less in certain environments. This is due to soil profiles being less suitable for this dewatering method. Across Europe, this method is nearly universal in its association with pipeline projects. Despite soil conditions in some locations, horizontal dewatering could still provide benefits.
3.1.4 Pressure relief wells
Wells designed to relieve pressure (sometimes called bleed wells) is a passive well designed to reduce water pressures in certain conditions. Confined aquifers or stratified ground near or beneath excavations are common circumstances where they are installed. Excavations made into the soil with low permeability above a confined aquifer often require relief wells.
In this frequently experienced scenario, the confined aquifer exerts upward pore water pressure, which destabilizes the excavation site. The whole site may heave upward due to the weight and shear strength of rock between the excavation base and the aquifer cannot balance the uplift force created from the confined aquifer. Relief wells are designed to resolve this issue. The ideal solution is a relief well which allows water to seep from the confined aquifer into the excavation.
Relief wells are drilled within a grid pattern on the excavation site. Wells must be installed before the site has reached below the piezometric level in the aquifer. As excavations reach below the piezometric level, water will overflow from the wells. This relieves pore water pressures and stabilizes the site. As water flows from relief wells, sump pumping is employed to transport it to a discharge area. Drainage blankets or drain networks may be installed to direct water to the sumps, which will prevent ponding in the excavation.
Because these wells are not directly pumped, they are classified as passive dewatering systems. Relief well systems require the indirect sump pumps within the excavation to adequately provide water control. This dewatering method requires installation along the pathways which facilitate ‘bleed’ from the aquifer. Installing relief wells in this manner ensures groundwater heads drive flow rather than pumping systems.
Most groundwater control systems use relief wells of large diameter, ranging from 100mm to 450mm, which are formed by drilling or jetting. These relief wells may be backfilled with sand or gravel and feature well screens. Smaller diameter drains may be installed for soil consolidation purposes, but these differ significantly from passive relief wells.
Relief wells are advantageous for several key reasons. They are inexpensive and simple. Many relief wells are simple, backfilled boreholes, which may use perforated well screens. Because relief wells are indirectly pumped, a large diameter borehole is unnecessary. This reduces drilling and installation cost. The sump pumps used in relief wells are more durable and widely available than their submersible, electric counterparts used in deep wells and other dewatering methods.
Another advantage of passive relief wells is their ability to cope with extremely low yield wells. Situations such as those involving low permeability stratum are likely to be low yield and cannot be accommodated for by most other means. Submersible pumps in these circumstances can easily burn out. Several passive wells will collect water in excavation sumps, where the sump pumps wait for adequate levels to activate. Borehole pumps are less suited to performing in this manner.
When designing relief well systems, the spacing between wells should be carefully considered. Flow rates may be anticipated to determine the necessary number of relief wells to handle water volume on-site. Sufficient distance between wells is important to observe, conversely, the distance should not be excessive. Wells too widely spaced may not account for variable ground conditions. If installed too far apart the wells may not properly intercept fissures and permeable zones. In these cases, destabilizing pressures could remain, creating heave between relief wells.
Primarily, bleed wells help to stabilize an excavation base. Deep cofferdams or shafts where the excavations are supported by physical cut-off walls or other structures are sites where stability concerns are of high concern. Excavation sites which feature chalk, mudstones, sandstones, and similar rock types or stiff clays are most in need of passive relief well systems. As relief wells overflow into the excavation, proper drainage networks are often necessary. If drainage blankets or drain networks are not installed, soils may be softened by the water, increasing on-site risks. Directing water to the sumps using the above systems is highly recommended.
Long-term pressure relief may be attained by installing relief wells as a part of permanent infrastructure. Sites constructed above confined aquifers may require permanent relief wells installed with screens and casings to allow periodic maintenance. Such wells may encounter waning performance after years of service.
Open-pit mines may sometimes use passive well systems to relieve groundwater pressures beneath the base of the pit. Low permeability layers which exist below the pit may create the need for bleed wells. Sometimes geological structures such as permeable fault zones may be drained into the pit to reduce pore water pressures and depressurize the mine. Pit pumping systems collect and distribute the water to discharge sites or reinjection points.
A wellpoint is an economic and versatile means of water control. Comprised of a small diameter, closely spaced, shallow well, well points are used for onsite dewatering at depths less than 6 meters. Specialized surface vacuum pumps are used to transport groundwater. Wellpoint’s systems work best in stratified and fine-graded soils. Additionally, wellpoint dewatering systems may be quickly installed, making it a versatile solution for sites with rapidly changing conditions.
Each wellpoint uses a small diameter riser pipe with a slotted filter at the base. The wellpoint pump connects to the header main, where it creates a partial vacuum to draw water. Water is then routed to a discharge point. Most sites employ well points around the perimeter of their excavation or parallel to a pipeline trench. These dewatering systems may be installed by auguring, drilling, or jetting.
Once a surface pump is attached to a wellpoint system, vacuum and flow are created. This limits drawdown to 6-meter depth. Stages of well points may then be installed at lower levels for greater depth of dewatering. While well points may typically be regarded as disposable, certain types of well points—such as steel self-jetted well points—may be retrieved and reused after the pumps are shut down. The advantages of wellpoint dewatering systems include:
- Simple maintenance requirements
- Capable of providing solutions to large projects and small-scale projects
- Most ground supports easy installation of wellpoint systems
- Can be used in tunnels to depressurize confined layers for construction
- Can be installed in difficult conditions with rotary drilling rigs
- Are quickly installed in a wide variety of site conditions
- Steel self-jetting well points are re-usable and efficient
Drilling a standard vertical well is a firmly established practice. Deviated or horizontal well paths have only become reliable with the advent of measurement while drilling (MWD) and logging while drilling (LWD) technologies which allow operators to place a wellbore precisely along the desired path. Geosteering uses the information gained while drilling to make trajectory adjustments to the well. These adjustments are essential to optimizing the well utility of any deviated well. Geosteering is typically used in:
- High angle deviated wells in thin formations where well production can only be achieved if the wellbore remains within a permeable zone
- Horizontal wells where remaining, within a fixed distance from fluid contact or overlying tight formations, is required
- Drilling where proximity to a fault is required to establish a fault location or determine if crossing the fault is desired
- Drilling along a fixed orientation to natural fractures
Geosteering is necessary for deviating a well, cuttings (hydrocarbon shows and readings), the transmission of LWD tools, and determining drilling parameters such as kicks, losses, rate of penetration, and torque. Often more difficult than anticipated, some of the most limiting factors include:
- Tools and technologies involved in decision-making processes, usually tools or technologies as far as 30m behind the downhole bit. This means if the bit is off of the desired Wellpath significant penetration into an undesired formation could occur
- High-angle wells prove difficult to transmit real-time data through MWD and LWD technologies, particularly as a result of bandwidth or battery limitations, high ROP, noise, or tool failures
- Data from cuttings may have a 2-hour bottoms-up time, certain equipment such as turbines may produce finely ground cuttings which are difficult to interpret. Oil-based mud, typically used in highly deviated wells, can cause difficulty in differentiating hydrocarbons
- Geological maps typically vary to some degree from in the formation, sub seismic faults of a few meters are commonly encountered, forcing the well out of the target zone. It can be difficult to then determine which side of the target zone the well has exited on. Absent faulting, thinning or deterioration of reservoir properties may be present which were unaccounted for
- When Geosteering assessments are entirely accurate, control of well deviation may present the team with problems. For example, when approaching a thin horizon at a steep angle, it may prove impossible to avoid exiting the desired horizon on the other side. Another possibility is experiencing bit drop or turn, which is difficult to control or prevent it entirely. Geosteering decisions can be impeded in long horizontal wells where the drill pipe must maintain tension with sufficient weight on bit (WOB) to maintain progress.
- When accidentally penetration a water-bearing zone, it may be incredibly difficult to prevent most of the well’s production from originating within this zone. Many horizontal wells severely limit the possibility of isolating certain zones or sections in long horizontal wells.
Even with the above limitations, Geosteering remains essential in drilling the most accurate, consistent, and productive well paths. Its proper application can singlehandedly determine whether a well or field is economically viable. Drilling in a permeable formation with tight formations on either side or sometimes in long horizontal wells, the path of least resistance may be followed by the bit. It may move through the most permeable layer, steering between and bouncing off of harder layers.
In the case of mining and hydrocarbon projects, Geosteering is an invaluable practice. Reaching the water-bearing zones for water control may be achieved through Geosteering the desired Wellpath for proper site drainage. Hydrocarbons, particularly those formations along fault lines, inaccessible otherwise, or unconventional require Geosteering techniques to gain access to. Additionally, many if not most drilling sites would be prohibitively expensive without Geosteering, which is an integral part of horizontal drilling and allows producers to create nearly 50 well paths from a single wellhead.
Without today’s Geosteering experts, drilling horizontal wells would not be a viable option for producers. Unconventional resources such as tight gas and shale oil would remain inaccessible. Many of the tools and technologies pioneered for Geosteering are required to produce these unconventional resources. The data gathered from advanced sensors play an instrumental role in advancing production goals for these projects. Typically, this data is interpreted to determine formation properties, directional, and drilling information.
4.1 Technologies used in Geosteering
Though attempts were made in the early 20th century, the first viable systems that remarkably improved efforts to measure and log information while the drill was completed in the 1970s. Early technologies included wired pipe, mud pulse, acoustic, and electromagnetic systems. These systems gathered measurement while drilling (MWD) data and saw rapid increases in effectiveness after World War 2.
By the 1980s MWD and logging while drilling (LWD) measurement technology included direction and resistivity, gamma, density, and more. Today’s Geosteering processes use these measurement tools in combination with petro-physicists, geologists, advanced modelling software, seismic data, image logs, MWD, and LWD to precisely and reliably create horizontally deviated wells. The most advanced drilling sites take these technologies to their next logical step: automation.
5 Remote Drilling Sites
Today’s data integrated, highly automated, cutting-edge processes allow for the planning and installation of remote drilling sites (remotely operated) which require little to no personnel to function reliably. Despite the dynamic processes involved in on-site operations, these sites have been tested throughout the last decade. Shell Upstream Americas tested pilot systems in the Haynesville Shale in North America early this decade to surprising success. Deployments of this technology, despite the difficulties, have gained significant ground, such as those used in 2018 by Baker Hughes in the Appalachian Basin.
These remote direction drilling facilities promise several benefits over traditional sites, particularly when factored into large scale strategic considerations for producers. The most prominent reasons for pioneering this technology include:
- Increased number of directionally drilled wells, the input of foremost experts can be applied to the site while they train new staff at centralized locations, effectively doubling their impact on operations
- Fewer people commuting to and from rig site increases safety, reduces transportation risk to personnel, prevents the large crew from interfacing daily with on-site dangers
- Centrally located geologists, geotechnical engineers, and Geosteering experts can apply their skills to a large number of sites simultaneously, increasing the rate of decision-making across projects
- Companies claim these sites have reduced need for Geosteering corrections, decreasing doglegs and maintaining the horizontal section more precisely. Casing wells becomes easier while ideal pay zones will produce greater recovery of hydrocarbon resources
Operationally, it is quite clear that the benefits of operating remote sites have every likelihood of overtaking large crews operating on site. The business case for remote drilling sites became clear as companies realized the need to address the “big crew change,” where an entire generation of oilfield experts would retire without proper replacement from upcoming generations.
Producers determined that leveraging competent and experienced staff over numerous operations would provide the most ideal solution for this situation. Additionally, if their experts could use their skills from a centralized location, several key benefits could be gained, particularly:
- Dramatically improved production rates and reserve recovery
- Improved efficiency and reduced waste in drilling rig and site costs, in effect, lean production or lean manufacturing principled operations
- Improving safety by reducing occupational hazards and risks, removing rig operating crews from harm’s way
- Ideal solutions for high-volume production from certain plays, which require thousands of production wells; this need defied conventional crew models for well construction
- The widely beneficial solution to the “big crew change,” issues facing the energy industries
While the business and operational case for remote drilling sites have long been established, the technological infrastructure required to remotely operate sites was underdeveloped by the early 2000s, when Shell and others began to experiment with more automated solutions. The Drilling Automation and Remote Technology (DART) centres deployed by Shell in 2010 were a milestone in the development of remotely operated drilling sites whose capabilities included directional drilling as well as data communication and storage through cloud-based systems. The first operations conducted by these remote sites in Eagle Ford Shale benchmarked in the top quartile for performance compared to competitors.
These early experiments with remotely operated sites showed 90% increases interpretation and decision-making speed, allowing near-real-time, proactive Geosteering. This significantly improved wellbore quality, tripping times, and case-running times, producing highly consistent increases in drilling performance. DART operations within Haynesville and Eagle Ford Shale were able to stay within the target zone 100% of the time while drilling directional wells, a feat unaccomplished until DARTs application. DART programs provided a remarkable return on investment to Shell throughout its early trials.
Producers around the globe have adopted many of these automated processes to develop their own remotely operated sites. Most commonly they may be found in harsh environments or locations best suited to their strengths. Remotely operated sites remain a rapidly growing practice that is being adopted for a wider variety of scenarios across industries that use drilling rigs.
Central to many of today’s drilling projects are custom-engineered drilling rigs capable of effective and reliable operation at remotely located sites. These operations, particularly those related to mining and hydrocarbon projects, rely on water control for their effective execution. For these projects to remain commercially viable, skilled geologists and petro-physicists use a broad range of tools and software to precisely guide the wellbore to target zones where they are the most effective and productive.
Though these processes have undergone continual refinement since the early 20th century, the last two decades have dramatically improved the capabilities of drilling rigs. Only recently have producers been able to consistently drill horizontal wells with accuracy and precision. Though applying these techniques to custom-designed or mobile drilling rigs can be demanding. Successfully applied, producers may feasibly access high-quality resources from the most demanding environments.
The most challenging environments present designers with the opportunity to pilot state-of-the-art technology designed to automate drilling sites. These remotely operated sites function with little or no crew. Once established, these remote sites are nearly autonomous, relying on centrally located experts as decision-makers.
Remote drilling sites have been tested in harsh environments with complex on-site requirements. These sites have been largely successful. Data indicates a remarkable improvement in drilling consistency and well production. Such sites provide producers with possible solutions for several key issues facing the rapidly changing, tech-heavy energy industry.
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