In its basic components drilling mud (drilling fluid) is bentonite clay and water mixed with some polymer additives to give it the required gel strength, viscosity and plasticity. Drilling fluid is crucial to any trenchless project involving drilling under the earth, as in oil and gas exploration, and in pipeline installation projects utilizing trenchless methods, such as horizontal directional drilling (HDD).
Drilling fluid helps in stabilizing the borehole, lubricating the drill bit, transporting the cuttings out of the borehole, and in suspending the cuttings in the fluid in case of a trip or when change is required in the downhole drill assembly.
Project Over, Fluid Spent – Now What?
Once the borehole is completed the drilling fluid has completed its role – now what? A decade ago, the standard procedure would be to contain the drilling fluid in an earthen pit and at the end of the project to spread the excess fluid and cuttings at site and backfill the pit.
Try doing that today and you’re sure to get your license suspended. Today, based on the mud type, Waste Disposal Regulations are classified into water-based, oil-based and synthetic-based muds. Water-based muds use fresh water or salt water as their primary constituent, while oil and synthetic-based muds use refined oil or synthetic material as their primary constituent. Disposal of water-based muds are subject to the least prohibitions and accounts for over 80% of the market. Offshore disposal of water-based drilling mud and cuttings is permitted by most countries.
As per the U.S. Environmental Protection Agency (EPA), spent drilling mud is special waste. The drilling process generates used drilling fluid and drill cutting, both of which need to be disposed safely, away from ground water sources and fields, to prevent contamination.
Regulatory practice for waste disposal has undergone radical changes since the 1980s, with acts such as Resource Conservation and Recovery Act (RCRA), Clean Water Act (CWA) and Toxic Substance Control Act (TSCA).
Every contractor should consider the environmental regulations regarding waste disposal prior to bidding, because today drilling waste management has become a major part of a contract. It is necessary for every project to consider drilling mud containment, mud recycling using solids control or other treatment, and mud treatment prior to disposal.
The prevalence of social media, federal regulations, and public awareness of environmental concerns, has prompted project owners and contractors to take drilling mud disposal very seriously.
Spent Drilling Mud Management
The most popular drilling mud is water-based because it is more environmental friendly than oil or synthetic-based drilling mud, and therefore easier to dispose. However; it’s the additives in drilling mud such as polymers, emulsifiers, inhibitors, and weighting materials such as Barite, that cause the concern. If disposed without adequate treatment, it can adversely affect the purity of groundwater sources close to the project site. Some methods used for safe disposal of drilling waste are:
- Dewatering and backfilling of reserve pit.
- Solidification or chemical fixation.
- Land farming of drill cutting and drilling fluid.
- Microbiological treatments.
- Thermal desorption.
Drilling waste management depends on project site, project type and type of drilling fluid. Since every project is different, waste management methodology and guidelines will vary. However, recycling drilling mud has become popular because it saves cost associated with mud quantity, and disposal. Recycling the drilling mud can limit the consumption of mud additives and reduce volume of waste.
The circulated mud is recycled through vibrating screens, de-sanding and de-silting hydroclones after which it comes back to the mixing tank for recirculation. When the project is over, the remaining mud after recirculation still needs to be disposed.
For water-based muds, the bentonite and cuttings have to be separated first. The mud is subjected to coagulation, flocculation and dewatering, after which the liquid phase is safe to be discarded into the sewer network or river, while the solids can be disposed to a landfill.
Drill cuttings recovered from the drilling waste can also be put to use in stabilizing surfaces prone to erosion, such as roads and drilling pads. It can also be used instead of aggregates in concrete and for manufacturing of bricks and blocks. A possibility proposed and researched by the U.S Department of Energy is to use drill cuttings as a substrate for restoring coastal wetlands.
Different technologies such as solids control, onsite disposal, incineration, bioremediation, waste recycling, and thermal desorption are available for companies to implement and manage drilling waste.
The cost of disposal varies depending on transportation, transportation equipment cost, special additives and personnel required. Though tedious, drill cutting and drilling mud recovery is a very sustainable environmental friendly process.
Since regulations pertaining to disposal have to be followed by the contractors and owners, it is practical to utilize proper disposal methods most suitable to the site and project conditions. Recycling and reusing muds is not just environmentally friendly, it is also cost effective and time saving.