Horizontal directional drilling (HDD) and other trenchless methods of pipeline installation produce drilling waste. Although the composition of the drilling waste from HDD is typically a relatively harmless mixture of water, bentonite clay, subsurface ground cuttings, and some other non-toxic additives, the handling and disposal of drilling waste is regulated in the oil and gas industry and the development of a responsible plan to safely dispose of drilling waste is required.
The disposal plan should not only protect the health of those who work or live near drilling sites, but also the environment. CCI Inc. — a leading expert in trenchless pipeline design and execution — offers several disposal options outside the traditional landfill and land farming techniques.
Land Disposal Options
Onshore drilling sites have several options to dispose of drilling waste. Understanding the environmental impacts will help determine the best method for disposing of waste from drilling. While the Resource Conservation and Recovery Act (RCRA) in the United States exempts oilfield waste from the hazardous waste requirements of the US federal government, sites still need to follow state regulations. In Canada, the federal Canadian Energy Regulator Act and its associated regulations do not address the handling and disposal of drilling waste directly, however, each province has rules, directives and regulations that must be complied with during HDD operations.
CCI offers several alternative drilling waste disposal options in addition to the more traditional methods. We'll discuss their non-traditional options for disposal as well as the pros and cons of each technique.
All HDDs require the use of drilling fluid to circulate the solids back to the rig where it can be separated into drilling waste and drilling fluid. By processing the drilling fluids coming back to the rig, companies are able to reuse the fluids during operation, which can help reduce the impact to the environment and may reduce some of the costs for the project.
One piece of equipment used to process the used drilling fluids is the centrifuge. Centrifuges, as the name implies, use centrifugal forces to mechanically separate the heavy solids from the liquid portion by spinning the used drilling fluids at high speeds. This process is called reclaiming. It helps to reuse the drilling fluid by reducing the mud weight and can greatly reduce the amount of drilling waste created on an HDD project. It also allows for more straightforward disposal of the solid waste resulting from the centrifuge.
There are some benefits to using a centrifuge system. With no new additives introduced into the drilling waste, the centrifuge has a high rate of processing while effectively reducing mud weight. Using a centrifuge to remove solid waste can help to minimize downtime for maintenance and repairs of the reclaimer and pumps.
Federal regulations may exempt oilfield waste from hazardous waste regulations; local landfill analysis may prohibit the inclusion of contaminants, such as hydrocarbons and metals. Encapsulating the waste through the introduction of additives can contain the pollutants. Through encapsulation, the waste is stackable and can pass landfill analysis.
For most applications, the bentonite clay additives used to encapsulate the contaminants bind to it chemically. The reaction creates a 1000-year bond to keep the metals and hydrocarbons in check. Encapsulation works well for mountain HDD work, which can produce metal contaminants, and regions with subsurface hydrocarbon sediment formations, which often result in hydrocarbon contamination of the drilling waste. By introducing the encapsulation additives, waste classification can be reassessed through laboratory analysis and often will adjust the class to make the waste more manageable while maintaining regulatory compliance.
Unlike with centrifuge systems, waste contained through encapsulation requires onsite storage. Disposal at a special landfill may be necessary which could require trucking costs to the final disposal facility. However, since encapsulation typically reduces the waste classification, the disposal cost is typically reduced.
Solidification is a process involving the introduction of additives to the semi-liquid drilling waste coupled with mechanical agitation to create a stackable, more manageable product which can then be sent to landfill, providing the landfill’s analytical requirements are met. The solidification agents create a waste product that maintains its stackable form and reduces the need for traditional bulking agents, like sawdust or wood chips. The stackable waste can then be managed by traditional disposal methods if within the regional regulatory requirements or can be transported easily to a local landfill.
As only solid waste can go to landfills, the use of solidification agents helps to allow this waste to go directly to local landfills, rather than more expensive options, like deep well injection sites, which can be very costly.
One primary negative in using traditional or additive-based solidification agents is the slight increase in the overall volume of waste. However, depending on local landfill regulations, the use of these agents can reduce disposal costs. Most agents are natural or earth-based products that can be disposed of in local landfills with limited risk of hazardous waste regulations.
The cost of solidification includes an excavator, operator, and cost of the additives. While this can add up, the reduction in disposal costs can help to offset the usage.
Dewatering is the method of processing drilling waste to separate drill fluid into solids and clear liquid. To accomplish this, CCI uses mechanical interactions, such as a centrifuge and chemical interaction through additives, such as a flocculant. Solid waste produced by this method can be disposed of in a landfill that can accept this kind of waste or other conventional disposal methods.
Using a dewatering system for drilling waste disposal, companies can recycle the liquid reducing the total water consumption and overall waste production. It also reduces the amount spent on drilling fluid as much of it can be reclaimed and reused. This can be beneficial in situations where large volumes of drilling wastes are produced such as large diameter pipe installations or long crossings. In some situations, freshwater influx from surrounding formations can contribute to the total drilling waste volume and this method can be used to reduce the disposal costs.
The primary negative effect of using a dewatering system is that the process changes the chemical composition of the water. The stripped water then has a new chemical makeup that contractors may not be familiar with using. In this event, the contractors may choose to dispose of the clear water instead of reusing it. However, clear fluids produced by dewatering can be disposed of using conventional methods, providing analytical results fall within acceptable parameters for conventional disposal.
The cost of using the dewatering system disposal method is variable, dependent on the equipment necessary to perform the task based on the job site.
Drilling fluid reclamation for HDD multi drill applications helps to reduce overall waste. Having all the fluid processing for multiple HDDs that are in relatively close proximity to each other all take place at one site can allow for significant efficiencies. To do so, a central site designated by the drilling company is necessary. The method to process the drilling fluid reclamation central site can incorporate many of the above mentioned methods to process the mud and reclaim the fluids which can then be mixed with drilling additives to create new drill fluids and stackable solids. The main site needs a project coordinator to coordinate with all onsite representatives. The coordinator is responsible for ensuring all drilling sites have the essential equipment, fluid, and trucking required to complete the project.
Using a central site minimizes safety hazards in a heavily populated area. There is a reduction in costs for trucking, disposal, and mud. A centralized reclamation site gives the crew the capability of building mud to customer specs without causing drilling downtime. It also allows for minimal downtime for repairs and maintenance on the reclaimer.
This method is only viable if there are multiple simultaneous HDDs occurring relatively near each other. If there are more than 30 miles between drilling locations, the use of a central site is generally not cost-effective for projects with such long distances between sites.
Facility solidification is available to those near large city centers, but not all large cities offer this service. To utilize this, a slurry or vacuum truck transfers untreated waste to the facility where it is processed and mixed with vegetative matter or sawdust. Once processed, it is transferred to the landfill and is entirely managed by the landfill.
Using facility solidification means there is no processing at the trenchless site. There is no post-disposal monitoring, as the liability associated with disposal is released to the facility once it is received. There is a limitation of only having a few locations near larger centers on which sites can take advantage of facility solidification.
The cost of this disposal method varies significantly from site to site due to location-specific trucking fees and landfill tipping fees.
Other Unique Methods
Some HDD projects require adaptive methods to dispose of their waste due to the remoteness of their location. A few other, lesser-used options for drilling waste disposal include onsite solidified waste disposal, mine/tailing pond disposal and off-shore disposal.
These unique methods can reduce costs by preventing high trucking costs to transport waste to the disposal site or facility. The techniques could also be tied to the owner's operations and in conjunction with other disposal methods.
Due to the nature of these disposal methods, there may be permits required through local regulators. These take expert planning and must be accounted for before drilling begins.
Costs have a wide range for these projects. The cost is highly dependent on the method, and what transportation, tipping, and permit fees are required.
There are different ways to dispose of drilling construction material. Cost considerations are only a small part of the options facing drilling companies. Potential ecological and environmental effects hold great significance when conducting drilling waste disposal and reclamation. Using alternative techniques such as those provided by CCI, companies can find an optimal solution and also curtail some of the disposal costs.