WASTE MINIMIZATION PROGRAM CAN REDUCE DRILLING COSTS

Charles R. Hall, Richard A. Spell
Oryx Energy Co.
Houston

By systematically eliminating the sources of drilling wastes, waste management programs can reduce the costs of location cleanup and restoration.

Stiffer environmental regulations, "cradle to grave" responsibility for wastes, public concern for the environment, increased landowner restrictions, and changes in corporate philosophy all result in higher costs of handling drilling wastes.

Effective waste minimization has become a critical part of drilling operations.

Waste management must involve all aspects of a drilling operation. During each phase of a well, the goals must include reducing waste volume.

The main purpose of waste minimization is to reduce waste volumes through prevention or recycling.

This can be accomplished by managing drilling operations intelligently by finding alternative uses on site for materials, segregating wastes to prevent further contamination, and using materials less damaging to the environment.

Waste minimization has one key rule: "Don't make a big problem out of a small one."

The waste minimization process is primarily driven by limiting liquid wastes. The liquid portion of a drilling fluid is generally the most abundant waste and is usually the easiest to control. Solid waste from the drilling operation often requires more effort to control.

Historically, oil and gas drilling operations have been conducted with little concern for the amount of waste produced. Wells were drilled as quickly and cheaply as possible. Typically, the cleanup of drilling sites was the responsibility of production personnel.

Because drilling personnel had little to do with the waste cleanup, they did not have a clear picture of the costs and difficulties involved.

Locations were often constructed larger than needed because it was "always done that way," or it was easier to build a big location than to design a compact location based on specific rig dimensions and layout. Usually one reserve pit was built, and it was large and always full. Most of the on site waste was placed in the reserve pit during or just after drilling. At the end of drilling, wells were tested into the reserve pit. The pit was then closed in place with the cleanup and reclamation considered complete.

Those days are gone.

It is now essential to leave a drillsite in an environmentally acceptable and aesthetically pleasing condition. Oil and gas operators must address the remediation of the drillsite. This process actually begins during the planning of the drilling operation and continues through the location construction, drilling, and completion or plugging of the well. The minimization process requires an interactive, dedicated team of field, technical, environmental, and clerical personnel.

The waste minimization process has four main parts:

Drilling program
Drillsite construction
Drilling and completion operations
Cleanup operations.

DRILLING PROGRAM

Waste minimization begins with the design of the well bore and mud system. Factors in well design, such as hole size, casing seat depths, mud programs, hydraulics, and solids control efficiency, impact the success of waste minimization.

Obviously, the larger the hole, the more solid wastes generated. Note the volume differences between an 83/4in. hole, a 97/8-in. hole, and a 121/4-in. hole. The 83/4-in. hole produces 0.4176 cu ft/ft of drill solids while the 97//8-in. hole produces 0.5319 cu ft/ft (27% more) and the 121/4-in. hole produces 0.8185 cu ft/ft (96% more). Thus, it is important to drill the smallest hole practical to reduce the volume of drill solids. This should be a common practice in well planning simply because of the cost savings associated with smaller pipe and equipment.

Well bores are not always large by design. High annular velocities can cause excessive hole washout which, over a long interval, can produce vast quantities of solid waste. Adequate hole cleaning must be balanced with preventing well bore washout. If possible, the mud system should be designed to reduce the effects of hole washout.

The mud system should be environmentally sound. Many mud additives contain chromium, barium, or chlorides. Contaminants and certain mud properties can prevent recycling of the mud or on site disposal of the cuttings. Thus, large amounts of liquid or solid material may need to be hauled to commercial waste disposal sites, and this option is often expensive.

Casing programs may also affect the waste generation process. An intermediate casing string or liner isolating a salt section or high pressure zone may become cost effective if such zones can contaminate the reserve pit. In areas where drilling along salt domes is common, parts of Mississippi for example, salt cuttings could contaminate entire reserve pits. It is important to perform economic analyses comparing costs of extra casing strings to the costs (transportation, disposal, and remediation) of the contaminated mud.

LOCATION DESIGN

The construction of the drillsite must take into account several factors:

Topography
Rig size and equipment layout
Anticipated volume of cuttings
Possibility of contaminated cuttings
Mud program
Lease, regulatory, and surface owner restrictions.

The location planning includes a site evaluation to analyze the layout for water runoff problems. The site evaluation should include a visual inspection of the surrounding areas for drainage patterns on neighboring properties, proximity to bodies of water, and proximity to residences and buildings.

After staking the location, the drilling foreman or the environmental coordinator should indicate the least disruptive access route, the orientation of the site, the drainage patterns, the availability of areas for on site waste treatment, and possible existing contamination.

Trees cleared from the location and access roads become a waste that must be handled. Location crews should remove as few trees as possible.

If it appears that the site was used previously for disposal, oil field activities, or other industrial activities, an in-depth evaluation should be conducted. At a minimum, this should include a visual evaluation and soil sampling of suspect locations. If problems are anticipated, a Phase I or II site assessment can prevent many claims for damages from previous contamination.

Such a costly disposal operation in South Louisiana resulted from the construction of a reserve pit on an old drilling site with excessively high barium levels. The reserve pit material from the drilling operation became contaminated from the background levels of barium left by the previous operator. As a result, a large volume from the reserve pit had to be expensively disposed. A Phase I or II assessment may have detected the high barium levels before commencing operations, giving the operator the opportunity to relocate or repair the site.

If landfarming will take place on site, the proposed area should be sampled to determine the background conditions. The soil conditions determine the waste loading capacity for the site. Water table data also determine the suitability of the site for waste treatment.

Identification of the soil type aids in the planning of pit construction and waste management techniques. County soil surveys give information about the engineering properties of the soil to determine its suitability for levee or pit construction.

The size of the location must be as small as feasible. There is no reason to build a 400 x 400-ft location when a 300 x 300-ft location will suffice. The smaller location disrupts surrounding areas less and is cheaper to build.

The location should be designed to keep rainwater runoff away from both the reserve pit and the rig to prevent contamination of the rainwater. This is especially important in areas of high rainfall. For example, a 1-in. rain on a 300 x 300-ft location will generate over 1,300 bbl of water. If that water enters the reserve pit or becomes contaminated in any way, it will become an expensive waste to manage.

To segregate drainage, the location should be sloped, or "turtle backed." Rainwater from around the rig, mud tanks, fuel tanks, and chemical storage areas is then separated from uncontaminated rainwater from other areas of the location.

The reserve pit should be designed to prevent collection of runoff water. Runoff water should be collected in a sump or separate pit from which it can be discharged, treated, or used around the rig.

Off site runoff water can increase disposal costs and may possibly bring contaminants. To prevent this, ring levees may be used around the location, but the ditches should be segmented to isolate local spills.

Through effective planning, an operator can lower location costs (smaller location to build and board) and lower disposal costs (lower volumes of waste and fewer surprises).

RESERVE PITS

The drilling engineer must determine if a reserve pit will be the best system of handling and storing drill cuttings, mud, and water. A reserve pit may be the best waste management technique if there is adequate space for landfarming around the site, if it appears that wastes can be landfarmed, and if the surface owner will allow landfarming. Closed systems (without pits) are being used more frequently if construction of a reserve pit is not feasible or if it is cheaper to handle cuttings without putting then in a pit.

Pits should be located to minimize hazards to the surrounding area. This may require the operator to dig the pit rather than simply push up an earthen levee.

Any pit which may contain a contaminant should be lined. Some states already require impermeable liners for certain pits. Without an impermeable liner, the pit fluids could leach into the ground and possibly contaminate groundwater. This is of special concern for salt water and salt cuttings. The cost of a liner is small compared to the cost of any contamination cleanup.

The pits should be designed as small as practical. One rule of thumb for pit construction is to allow 2 bbl of drilling waste for every foot of hole drilled. The pit volume should be built assuming vertical pit walls, plus 2 ft of freeboard to meet most regulatory requirements. Most reserve pits have sloped walls resulting in about 1112 bbl of actual pit volume per foot of hole. This is an extremely small but manageable volume. The rig personnel must continuously monitor and regulate the volume of material entering the pit.

Reserve pit systems should consist of multiple pits, with a minimum of two and preferably three pits (Fig. 1). These isolate drill cuttings and contaminants from the main part of the pit system. One consideration is the use of pumps to move fluids between pits rather than using overflow ditches. Pumps help eliminate inadvertent contamination of all the pits because fluid does not transfer automatically; it requires energy or physical effort.

The reserve pits must be designed to allow for processing the material while it is in them. By managing the reserve pit fluids efficiently, waste generation can be reduced, and problems with handling the waste can be minimized.

On two recent wells in South Louisiana, Oryx Energy Co. successfully used a managed reserve pit system. The overall disposal costs were reduced by 50-75%, and the volume of waste hauled to commercial disposal sites was much lower than on comparable wells.

DRILLING OPERATIONS

During the bidding process, the rigs should be inspected while on other wells. The drilling engineer should conduct a second rig inspection during the early part of drilling the well while the mud system is still relatively new. Successful minimization operations require environmental awareness meetings as well as an environmental audit of the rig prior to spudding.

An inefficient drilling operation can use up to 300 bbl of water/day in operations other than actual drilling. Water meters should be installed and monitored to control water use. All water hoses should have shutoff valves, preferably automatic. Rig wash hoses should be equipped with high-pressure, low-volume sprayers, and rig washing should be limited to only what is necessary to maintain safety. Reserve pit water should be reused to clean solids control slides, and ring levee ditch water can be used for makeup water in the mud system.

It is good practice to handle all mud systems as if they were oil-based muds. This results in better supervision of the equipment and less waste produced.

It is important to require zero discharge where contaminants such as lubricating oils are present. Drip pans should be used under leaking machinery until the leak can be fixed. The collected oils should be stored for reprocessing or proper disposal. This is especially true for lubricating oils classified as hazardous waste under Environmental Protection Agency guidelines. Lubricating oil spilled into the reserve pit could cause the entire pit contents to be considered as hazardous.

Another possible problem source is the mouse hole. Because the mouse hole is generally 20-40 ft deep, mud contaminants or salt water might leach into the ground. The bottom of the mouse hole should be cemented to prevent drilling fluids from reaching groundwater if the water table is shallow.

The efficient use of solids control equipment minimizes the dilution water needed to maintain acceptable drill solids in the mud system. A mud with 6% drill solids can require up to 16 bbl of water for every barrel of solids. Specialty solids control equipment such as centrifuges and cuttings washing equipment can significantly reduce waste by concentrating the solids or isolating contaminants.

Solid waste (not drill solids) from the drilling operation includes municipal-type trash (food waste, paper, etc.), mud additive bags, dope pails, and drums. Typically, paper and plastic trash are burned on location. Local regulations may prohibit burning certain trash because of the possibility of chemical contaminants. The trash should be separated into bulk containers for proper disposal off site (Fig. 2). Any vendor-supplied item such as sacks, pails, or drums should be returned to the vendor for recycling or proper disposal.

Mud system wastes can be reduced by limiting the size of the reserve pits, controlling water usage, and reusing water whenever possible.

PERSONNEL TRAINING

It is essential to get the drilling foreman involved with the goals of the waste management program before spudding the well. If the foreman understands the regulatory constraints and is given the opportunity to try his ideas, he can become the most effective part of the program.

An effective means of communicating the waste minimization program to the entire rig crew is to hold an environmental meeting at the beginning of each shift change. The details of the waste minimization program are discussed so that each person understands his role. Each worker must also understand why certain things are being done differently.

The waste management process involves the rig personnel directly-they become aware of the need for waste management and understand the problems resulting from improper procedures. Ultimately, the rig crews will become more conscious of the effects of their actions.

Because they are directly involved with the operations, they may come up with some innovative methods and techniques of waste minimization.

MUD RECYCLING

If a material can be reused or recycled, it is not considered a waste. An excellent example is weighted drilling mud. If at all possible, the drilling foreman should contact a local drilling mud company to inquire about selling the mud to it. The amount of money received for the weighted mud may not seem attractive compared to the initial cost, but it is definitely better than paying for disposal.

Salt water is often purchased for the mud system as kill weight fluid. Once the salt water enters the reserve pit, the liquid has to be hauled away as a waste product.

On a drilling location in South Texas, the foreman isolated the salt water from the rest of the fluids. The supplier took back the clean salt water and was able to sell it again. Although the well did not receive a credit for the reclaimed salt water, the disposal costs were significantly lowered.

If an operator is drilling a multiwell program, transferring the mud from one well to another may be a viable option. In the Carthage field in Panola County, Texas, a specially designed mud used for drilling through a highly pressured zone followed by a depleted zone was reused by an operator in a number of wells. The transportation costs were far lower than the costs of building new mud systems.

If the pit water is clean enough, it can be used in the mud system or around the rig to wash the rig or to wash mud slides (Fig. 3). This is important because a large portion of the daily water used on a drilling rig is for cleaning.

Another source of waste is cooling water used on slush pump rods.

This water can be reused in the mud system instead of allowing it to fall into the rig sump.

SITE RESTORATION

If the drilling operation is managed properly, cleanup and restoration operations should be fairly routine. The key is to keep problems small and easy to handle, primarily by isolating small volumes of highly contaminated waste from large volumes of uncontaminated material.

An example of the importance of this occurred recently on a well drilled by Oryx near New Orleans. The barite-contaminated cuttings from the bottom portion of the hole were inadvertently mixed with the uncontaminated native cuttings from the upper hole. Instead of 5-10 loads of material hauled to commercial disposal, 38 loads were hauled to disposal. There are five main methods of drilling fluids and cuttings cleanup:

Burial
Solidification
Landfarming
Annular injection
Commercial disposal.

It is typically better to handle the waste products on site through some of the first four methods than to haul them away for commercial disposal. Commercial disposal sites pose major risks because of possible Superfund responsibilities. Some companies have addressed this problem by purchasing specific sites where only their wastes can be deposited. A commercial site, no matter how good it is now, could pose a serious problem in the future. This does not mean that commercial disposal sites should be avoided. However, commercial disposal sites must be used judiciously. The sites must be evaluated prior to delivering any material.

On site waste management is generally easier and should be used whenever possible. If possible, the mud and cuttings should be spread through landfarming (this is not considered a waste).

Often, waste disposal can best be done through annular injection. There are several ways to maximize the use of annular injection. For example, a cuttings washing unit can separate the barite from the cuttings.

The barite and fluid can then be handled through annular disposal, and the remaining cleaned cuttings can be landfarmed. Another option is a portable cuttings grinding unit which will reduce the size of cuttings for annular injection.

Solidification can make some material suitable as landfill for the location. However, burial of whole mud and cuttings is not recommended because experience has shown that this leaves the material in a condition that prevents it from being readily assimilated by the environment.

In some states, such as Louisiana, burial is highly restricted or impractical.

Waste management and minimization is becoming a major part of the drilling operation through financial and operational commitments. A poorly managed waste management/minimization program takes time and money away from the purpose of the drilling group-drilling wells. A well-planned waste program will hold down costs and can easily be incorporated in the drilling operation.