INFLUENT/EFFLUENT APPROACH TO MUD FORMATION REDUCES TOXICITY

Christopher J. Burke
Argonne National Laboratory
Washington D.C.

An influent/effluent approach to formulating drilling mud reduces the toxicity of mud discharged offshore because potentially contaminating additives are considered and approved for the mud system design before the well is spudded.

Conventional approaches address the toxicity of drilling mud when it is ready for discharge or disposal, after any additives have been mixed into the mud.

The influent/effluent (pollution prevention) approach facilitates industry compliance with environmental regulations because mud additives are already approved when the well is drilled. With this approach, operators choose mud formulas, sometimes substituting additives, that will not have difficulty meeting required toxicity limits for discharge.

In terms of volume and toxic pollutants, drilling muds and drill cuttings are among the most significant waste streams from exploration and development operations. Under the Clean Water Act, the Environmental Protection Agency (EPA) regulates discharges of all contaminants, including drilling muds, into U.S. waterways and offshore areas. EPA uses technology-based effluent standards in issuing discharge permits to onshore and offshore operators.

EPA has several regulatory approaches to limit toxicity in drilling muds on offshore drilling platforms and to reduce toxicity of drilling muds discharged offshore. EPA Region X for offshore Alaska, for example, uses an innovative approach that emphasizes pollution prevention. In contrast, other EPA regional offices use a more traditional command-and-control regulatory approach.

The Region X approach includes collection of influent and effluent data, development of a comprehensive data base of technical information, and prescription of specific mud formulas. This influent/effluent approach reduces uncertainty and guesswork, enhances the use of innovative technology, and lowers toxic discharges compared to the standard EPA command-and-control approach. The influent/effluent approach provides a model for future efforts to incorporate pollution prevention into regulatory development and implementation.

Limitations imposed on the disposal of drilling muds by offshore operators can have a large impact on the economic feasibility of operations and can inhibit development of offshore hydrocarbon resources.

Although this study found no evidence that toxicity limitations promulgated by EPA were having a detrimental effect on offshore developments, it identified major improvements in technology application, process management, and selection of raw materials which reduce the toxicity of spent muds.'

MUD TOXICITY

The Clean Water Act required EPA to establish effluent limitation guidelines (ELGs) for major industrial categories, but not until early 1993 did the EPA promulgate complete ELGs for the offshore subcategory of the oil and gas industry. The offshore ELG requirements included limits on discharges of drilling muds, which are one of the largest volume waste streams in oil and gas exploration and development.

The ELGs require zero discharge of drilling muds for offshore operations within 3 miles of shore. Table 1 (17819 bytes) lists the requirements for discharges located more than 3 miles from shore.2 The ELGs for the offshore oil and gas industry are the only ELGs (available for more than 50 industries) that place a limit on toxicity.

ELGs specify a toxicity limitation of a minimum 96-hr LC50 of the drilling mud's diluted, suspended particulate phase of 3.0 vol %, or 30,000 ppm. (LC50 is the concentration lethal to half of the test organisms during the test period). Muds that do not meet this limitation are generally barged to shore for disposal, adding considerable expense to operations. Before this limit was established on Apr. 5, 1993, permit writers had to rely on best professional judgment (BPJ) to control toxicity in drilling mud discharges. Since 1984, however, permit writers in several regions used BPJ to justify using a 30,000-ppm limit in general permits issued to offshore operators in the Gulf of Mexico and California.

COMMAND AND CONTROL

EPA Regions IV and VI regulate offshore activities in the Gulf of Mexico, where about 90% of U.S. offshore activity occurs. These regions use a basic command-and-control approach that relies upon mandatory end-of-pipe testing, Specifically, a bioassay must be completed on each batch of mud used and discharged, including the mud discharged when the well reaches its maximum depth. The toxicity limit set in EPA's ELGs must be met prior to discharge of muds.

Permit writers in Region IX (California) use the same strategy but allow several exceptions which permit some flexibility for the operators. Permits issued by Region IX exempt muds from a bioassay test if one of the following conditions are met:

The mud is one of the eight generic EPA-specified muds known to comply with the toxicity limitation.
Each additive meets a specific bioassay test standard (LC50 100,000 ppm).
Other toxicity data for the additive are available, and from these data the EPA may reasonably conclude that the mud meets a specific bioassay test standard for additives of LC50 100,000 ppm.3

Region IX's modified approach still emphasizes demonstration of compliance with the overall toxicity limit for each batch of mud used. Except for the batch in use when maximum well depth is reached (for which a bioassay is mandatory), the demonstration of compliance may alternatively consist of toxicity calculations to show the mud is below the whole mud toxicity limit or exclusive use of generic muds and additives listed as acceptable for general use.

POLLUTION PREVENTION

An alternative approach, developed and implemented in EPA Region X, has been used for discharge permits issued to offshore operators in Alaska. Described as the influent/effluent approach, this method uses greater control over mud components and additives, detailed data collection, and preapproval of expected and planned discharges, instead of relying solely on toxicity limits. Bioassay testing is used as a compliance check.4

Prior to issuing a permit, Region X evaluates detailed data in the permit application describing specific mud components and additives. The toxicity of proposed muds is calculated, and each permit limits the discharge of drilling mud and additives to only those specified in the permit application.

Prior to 1993, permits issued in Region X contained no specific toxicity limit. Now, such permits require monthly monitoring for compliance with the drilling mud toxicity limit set in the new ELGS. A final bioassay analysis following well completion is also required. If a mineral oil pill is used to lubricate a stuck drill bit, the mud is sampled for bioassay prior to application and after removal of the pill.

Permittees must request case-by-case authorization to discharge specialty additives not listed in the permit. In these cases, the proposed mud or additive is evaluated based on available bioassay data for the proposed discharge. This evaluation consists of worst-case estimates of the cumulative-discharge toxicity of the mud/additive system, and this method tends to discourage use of toxic additives. At the conclusion of each evaluation, Region X makes a best professional judgment determination based on its cumulative toxicity estimates for the proposed mud/additive discharge and the EPA toxicity limit.

As a result of this approach to limiting toxicity of drilling muds, EPA Region X has established a data base containing inventories of mud component and additive products, product concentrations, and toxicity of discharged muds. This approach emphasizes careful planning by permittees, greater data input and feedback between regulators and permittees, and development of prescribed mud formulas that comply with EPA toxicity limits.

The regional office encourages the use of the least-toxic additives, not simply additives that will permit compliance with the toxicity limit. This approach puts the burden on the individual operator to prove to itself and EPA, through planning, control, and documentation of all influents, that discharges of muds will comply with EPA requirements.

If EPA disagrees that a mud will meet the limitation, it simply excludes that mud from the approved list when the permit is issued. The emphasis in this approach is not on compliance with an end-of-pipe standard, but rather on controlling and carefully selecting influents to ensure the final recipe produces an acceptable mud for discharge.

COMPARISON OF APPROACHES

Significant distinctions between the command-and-control and influent/effluent approaches result in different emphases by operators in complying with the permit discharge requirements.

The command-and-control approach used by most EPA regions focuses on controlling mud discharges that exceed the permissible limit of 30,000 ppm. The only exception to this requirement is the modified approach used by Region IX, whereby operators are given some limited flexibility in using mud additives that comply with the limitation or using additives that do not cause the discharged mud to exceed the limitation. Otherwise, this approach is traditional end-of-pipe effluent control with few, if any, restrictions on inputs. In the traditional approach, compliance is solely determined by the toxicity of effluent.

In contrast, the influent/effluent approach requires increased information input, planning, and forecasting of mud types to be used by operators. Operators are permitted to discharge specific types and volumes of mud that are preapproved (for toxicity limits). The permit stipulates that operators carry out detailed monitoring, control, reporting, and documentation procedures to ensure that mud and additives used are as nontoxic as possible. This approach encourages substitution of nontoxic additives and waste reduction, not just to comply with the toxicity limit, but to reduce toxicity to the lowest level achievable.

Compliance is determined in large part by influent control and documentation and is checked by bioassay testing for toxicity. Perhaps what is most innovative about this approach is the planning that operators are required to perform in developing the inventory of muds and additives to be used in drilling each well.

Thus, operators must plan their mud compositions in advance and plan for contingencies in an environmentally acceptable manner to minimize toxic discharges. Although this approach requires greater interaction between EPA and operators, the benefit is a reduction in drilling mud toxicity to the lowest possible levels, not just levels that comply with EPA's toxicity limitation.

In this sense, this approach embodies pollution prevention through the use of best management practices for controlling drilling mud toxicity.

In Region X, the influent/effluent approach can be easily applied to the relatively small number of operators in Alaskan offshore waters. This approach may require modifications to be practical for Regions IV and VI because of the large number of wells in the Gulf of Mexico.

The results of the Region X influent/effluent approach have not been fully documented, but according to EPA Region X, the results of bioassay tests on discharged muds in Region X are strikingly different from those in other regions. Region X reported that of 118 valid data points, 75% achieved a 100,000-ppm standard, more than three times as stringent as the 30,000-ppm limit now in effect.

These results are substantially better than those from the other regions.' These results were obtained without the use of a toxicity limit in the permits, but instead through careful planning, input control, and good management practices. The Region X experience suggests that compliance with the 30,000-ppm limit is not exemplary.

Furthermore, since adoption of the final ELGs, Region X is required to include the 30,000-ppm limit in its permits. Hypothetically, if Region X discontinues the influent/effluent approach and uses just the command-and-control approach, toxicity of discharged muds could actually increase, perhaps significantly, while still complying with the end-of-pipe toxicity limit.

OTHER CONTROLS

Both approaches use additional controls to reduce discharges of the two leading sources of toxicity in drilling muds:

Oil from the formation or added to the mud for lubrication
Heavy metals in barite (a major constituent of drilling muds).

Oil is the major contaminant in offshore drilling muds that require onshore disposal. An EPA Region IX survey of muds used by off-shore operators during 1984-87 found that 24% of the spent mud from platforms was taken to land disposal sites primarily because of oil contamination in the muds.3

Standard Oil of California (Chevron) reported that all 25 muds requiring onshore disposal were contaminated by oil and failed to pass the sheen test. In 23 of these cases, the contamination was caused by oil from the formation, and in two cases mineral oil and mud additives caused the contamination. In every case, Chevron was required by its permit to barge and dispose of the contaminated mud onshore.6

Exxon Co. U.S.A. reported that all of the spent mud barged to shore for disposal during the same 3-year period was the result of contamination from formation crude oil. The muds transported to shore for disposal were EPA-approved mud systems with approved additives, but these muds had become contaminated with oil from the formation.7 Limitations on the use of barite also have a significant affect on the toxicity of offshore drilling mud discharges. Final permits issued by EPA regional offices now restrict the use of barite to so-called "clean" barite (

It is preferable from an environmental standpoint to require uncontaminated barite for offshore operations where used drilling mud is discharged into the marine environment and to allow contaminated barite to be used onshore where spent mud is land disposed.' The two leading sources of mud toxicity are essentially controlled with requirements in place that effectively mandate the use of clean barite in offshore drilling muds and that prohibit the discharge of oil in such muds. One may wonder whether discharge-toxicity permit limitations are redundant and why they are needed at all if the major sources of toxicity are being controlled through other requirements.

The data to address this question are not yet available. Even if toxicity limits were dropped from the ELGS, EPA's antibacksliding requirements prevent removing permit limits on toxicity, although monitoring frequency could be reduced.

INDUSTRY EFFORTS

Largely as a result of the development of toxicity limitations in ELGS, offshore operators have adopted a number of pollution prevention practices that were previously not common operating procedures:

Avoiding oil additives when possible and taking measures to reduce oil contamination of drilling muds
Substituting clean barite for contaminated barite
Using alternative mud additives in place of more-toxic substances
Planning mud compositions thoroughly before a well is spudded to reduce waste and use of toxic components, especially as a result of the Region X influent/effluent approach.

The industry has made significant gains in improving technology to find acceptable substitutes that reduce the use of toxic additives in drilling mud. Perhaps the most far-reaching change has been the simple substitution of clean barite for contaminated barite, which reduced contamination by trace metals and controlled a major source of mud toxicity.

Efforts to develop commercially acceptable alternatives to toxic additives is a high priority for industry, and research and development in this area is continuing.

Mud technology has become much more expensive and sophisticated in recent years, and computers and specialized software are now used to simulate and plan mud composition. Proprietary software used by industry permits operators to assess mud strategies by simulating downhole conditions and the effect of specific additives. These tools will increase the use of sophisticated mud formulas and will facilitate compliance with ELGS.

Technology advances in the near future may identify economical alternatives to conventional drilling muds as well as substitutes for toxic additives. Identification and dissemination of information about these technologies is critical to the long-term success of EPA pollution control programs.

RESULTS

EPA's effluent limitation guidelines, which became effective Apr. 5, 1993, establish a technology-based limit of 30,000 ppm as the toxicity standard applicable to drilling muds discharged offshore. Muds not complying with this standard require onshore disposal, and thus increase operating costs.
The frequency of onshore disposal and the concomitant costs, however, have been minimized by sound operating practices, substitution of additives, and careful control of other potential contaminants. The industry has not experienced great difficulty or undue expense in complying with this standard.
The major sources of toxicity in drilling mud, contamination by oil and trace metals contained in barite, are already subject to EPA regulatory limitations. Technology advances and modifications in operating procedures and mud composition have helped greatly reduce the toxicity of drilling muds.
As industry operations incorporate these advances, the continued imposition of a toxicity limitation may be redundant. Thus, the limitation may not be warranted or necessary in all cases, although EPA requirements would retain toxicity limits in discharge permits.
The use of a pollution prevention approach, such as that used by EPA Region X, has several excellent advantages in reducing toxicity of discharges. This type of approach can improve industry operating practices, eliminate guesswork, and facilitate industry compliance.
Limited regional data suggest that the influent/effluent approach results in attainment of far lower levels of toxicity than conventional approaches. Collection and analysis of comparative performance data should be a high priority to assess the comparative advantages of the different regulatory approaches.
The ELGs for toxicity in drilling mud discharges may be outdated because of advances in technology and operating practices. These ELGs may also be inefficient in reducing pollution to the lowest feasible and economically achievable level and counterproductive in obtaining continuing improvements in discharge toxicity and reductions in pollution loading. Eliminating waste by controlling influents may be the most effective method of controlling toxicity in drilling muds.
Technology advances and resulting improvements in industry compliance may eventually reduce or eliminate the need for end-of-pipe toxicity standards. The ultimate goal of any pollution control strategy should be to eliminate the sources of pollution, ideally to the point at which regulation becomes unnecessary. The Region X influent/effluent approach provides a valuable model for future regulatory developments using pollution prevention.

REFERENCES

1. Work supported by the U.S. Department of Energy, Assistant Secretary for Policy, Planning, and Program Evaluation, under Contract W-31-109-Eng-38.

2. 40 CFR Part 435, Federal Register Vol. 58, No. 41, Mar. 4,1993.

3. Fact sheet for NPDES Permit No. CAO110842 (Platform Harmony) and NPDES Permit No. CA0110851 (Platform Heritage), prepared by U.S. Environmental Protection Agency, Region IX, San Francisco, May 26, 1992.

4. Fact sheet for NPDES Permit No. AK-005205-1, prepared by U.S. Environmental Protection Agency, Region X, Seattle, Apr. 9, 1993.

5. Personal communication with Kris Flint, EPA Region X, Seattle, on June 1, 1993.

6. Amberos, P., letter and data submitted on behalf of Chevron U.S.A. to U.S. Environmental Protection Agency, Region IX, San Francisco, Aug. 27,1987.

7. Lyons, C.G., letter and data submitted by Exxon Co. U.S.A. to U.S. Environmental Protection Agency, Region IX, San Francisco, July 2, 1987.