The remediation of mud-polluted drilling sites is very important for the oil industry, and field trials have been undertaken in the Southeast of Mexico in order to find a technology to remediate such sites.

Polluted material was composted in biopiles, of one ton. Some nutrients and straw were added to these piles to establish the required ratio of carbon to nitrogen and phosphor. A control pile was also constructed and monitored. Compared to the control pile, after a period of 180 d the concentration of total petroleum hydrocarbon (TPH) in the test piles decreased by a much higher extent (Rojas-Avelizapa et al., 2007).

Gas chromatography studies indicated the presence of alkyl dibenzothiophenes. The highest bacterial populations were observed during the first 30 d. These correlated with highest rate TPH removal, whereas the number of fungi increased at the end of the experiment (Rojas-Avelizapa et al., 2007).

Biodegradability may be expressed in terms of (Battersby 2005):

Test methods for assessing the biodegradability of environmentally acceptable lubricants have been critically reviewed and discussed. Examples are given, which show how confusion can arise through the use of different test methods.

It is recommended that the term “biodegradable” for an environmentally acceptable lubricant should only be used when the net amount of CO₂ production over 28 days, tested according to the OECD test Guideline 301 B, is at least 60% of the theoretical maximum (Battersby, 2005).

The CEC L-33-T-82 biodegradability oil CEC L-33-A-934 test is a widely recommended method for assessing the biodegradability of oil products (Battersby et al., 1994). This test applies to most organic compounds, and determines the overall biodegradability of hydrocarbons.

The ASTM D-5864 standard (ASTM, 2010) is similar to a modified Sturm test (Sturm, 1973), and measures the degree of aerobic aquatic biodegradation of fully formulated lubricants or their components, on exposure to an inoculum under laboratory conditions. A good positive relationship has been shown between biodegradation in the CEC L-33-T-82 standard and the mineralization to CO₂ in a modified Sturm test. A mathematical model describes these correlations (Battersby et al., 1992).

There are a number of options available to treat and dispose of oil-based drilling mud (OBM) drilling wastes, including land spreading and landfilling (Street and Guigard, 2009). Supercritical fluid extraction has also been used to treat this waste (Eppig et al., 1984). This is an extraction technique that uses substances at or above their critical pressure and temperature as solvents.

Supercritical carbon dioxide can remove the base oil from drilling waste, with extraction efficiencies of upto 98%. The hydrocarbons are unchanged by the extraction, meaning they may be recovered and potentially reused (Street and Guigard, 2009).

Methods for monitoring the impact of drill cuttings contaminated with OBMs in marine environments have been developed. They are based on the analysis of benthic fauna, on chemical analysis of the sediments, or on ecotoxicological tests on the marine macrofauna (Jorissen et al., 2009). Benthos refers to all living organisms on the sea floor.

Pollution by oily drill cuttings has a range of impacts on the marine environment, in particular the benthic fauna (Jorissen et al., 2009). These are:

It has been found that benthic foraminifera are suitable bioindicators of the anthropogenic enrichment in open marine regions (Mojtahid et al., 2006). They respond by an increase in the density of a number of tolerant or opportunistic taxa, and a progressive disappearance of more sensitive taxa. Large-sized taxa appear to be more sensitive than smaller foraminiferal taxa (Jorissen et al., 2009).

Most of the cuttings discharged from well drilling contain WBMs rather than oil-based or synthetic muds, which are assumed to cause only marginal effects on the benthos. However, an experimental study revealed a significant reduction in the number of taxa, abundance, biomass, and diversity of macrofauna as the thickness of deposited drill cuttings increased. This phenomenon was not observed for natural sediment particles (Trannum et al., 2010). It is therefore recommended that the opinion that water-based drill cuttings only cause sedimentation, i.e., burial effects, be reconsidered as the cuttings initiate a typical eutrophication response in the sediment (Trannum et al., 2010).

The exploration and production of North Sea oil and gas reserves has caused the accumulation of large quantities of drill cuttings on the seabed around drill sites. This complex mixture contains higher concentrations of certain metals and hydrocarbons than are found in the natural sediments (Breuer et al., 2004).

It is known that the hydrocarbons within the cuttings piles remain relatively unchanged with time, and a considerable proportion of the associated contaminants are likely to remain within the cuttings pile unless they are disturbed. This increases the tendency to exchange porewater and solids back to the seabed surface resulting in the possibility of exposure to organisms (Breuer et al., 2004).

Models are available to predict the potential environmental impact of the drilling fluid components, based on estimates of the initial spatial extent and thickness of accumulations on the seabed. These models are a valuable tool for both the oil industry and regulatory agencies (Pivel et al., 2009).

Among the most widely used models are the Offshore Operators Committee (OOC) Mud and Produced Water Discharge Model (Brandsma and Smith, 1999). The use of the OOC model allows the estimation of the effect of discharges into the sea, i.e., of drilling fluids and cuttings, and also of produced water. An automated validation system based on this model has recently been developed (Brandsma, 2004). After setting up the validation system, only a small amount of additional work is needed for repeated validations to test the model, even after changes with respect to maintenance and development. The validation system provides a complete record of all validation methods, data, and results.

In a case study, the OOC model was used for modeling discharges in a deep-water environment from a well located offshore Brazil. Data were collected during the drilling and discharge activities, which enabled the researchers to carry out a study based on real data, i.e., hindcast modeling (Pivel et al., 2009).

Comparing the results obtained by modeling with real field observations gave satisfactory results, but the prediction of the affected area turned out to be more difficult, because the results are sensitive to small uncertainties, which are mainly attributed to the discharge activities. Nevertheless, in areas where there is knowledge of the hydrodynamics, the OOC model can be a valuable tool to determine the potential impact of drilling activities (Pivel et al., 2009).

Applications of microwaves are increasingly used in oil field technologies, at least on the laboratory scale (Mutyala et al., 2010). Of particular interest are the application of microwaves to bitumen extraction, upgrading of heavy oils, and removing heteroatoms. In addition, underground heating of oil sands to reduce bitumen viscosity is possible, which allows such materials to be pumped to the surface. Microwave energy provides a fundamentally different method of transferring energy from the source to the sample. By delivering energy directly to microwave-absorbing materials, conventional issues such as long heating periods and energy losses can be minimized.

In North America, the only allowed frequencies for industrial use are 915, 2450, 5800, and 22,000 MHz. For laboratory uses, 2450 MHz is preferred, since it has adequate penetration depth for most laboratory reaction conditions.

A patent was launched in 1983, that describes the recovery of shale oil and heavy oil using microwaves for heating (Bàlint et al., 1983), which is still highly innovative (Cogliandro and Moses, 2009). Microwave energy has been shown to be effective in some applications, but it is not used commercially at present (Mutyala et al., 2010).

Oil-contaminated drill cuttings can be treated with microwaves. In contrast to conventional heating, the microwave energy is delivered directly to materials through molecular interactions with the electromagnetic field.

It was found that under favored operating conditions, the oil levels can be reduced to below 1%. Laboratory experiments revealed that 20 s of microwave treatment is sufficient to reduce the residual oil levels below 1%. A major drawback for the efficiency of this method is the moisture content, but increasing water content of the samples can potentially overcome such limitations (Shang et al., 2006). The effectiveness of microwaves for heating of a variety of materials are summarized in Table 20.2.

The penetration depth D_p is defined as the depth at which the intensity of the electric field drops to e₋₁ of its value at the surface. The penetration depth is approximately:

2.45 GHz at 10 kW cavity power and 22 s irradiation time was used. The effect of moisture content on residual oil levels at microwave heating is shown in Figure 20.1 and the energy consumption using various methods of stripping the organic material is shown in Figure 20.2.

Based on previous research the authors have developed a continuous microwave treatment system for the remediation of contaminated drill cuttings on a semi-technical scale (Robinson et al., 2010). A system capable of treating 500 kgh⁻¹ has been set up, which has demonstrated that the environmental discharge threshold of 1% oil can be achieved in continuous operation. The sensitivity of this pilot plant toward changes in the feedstock has been investigated. The system must process both slurries and granular solids. It has been found that when moisture content deviates from its nominal value of 6%, the system performance becomes lower, as the power to density ratio decreases.

The inclusion into lime, pozzolanas, Portland, or slag cement forms a cost-effective and reliable technique for the immobilization of large amounts of drill cuttings. Unfortunately, chloride ions retard the setting of the cement and the mechanical strength of the end-product is reduced. For this reason, the disposal of sodium chloride-containing drill cuttings is still problematic.

The addition of orthophosphate seems to form a continuous and weakly soluble network in the cement matrix, which reduces the release of the salt. Actually, apatite and hydrocalumite are formed. These phases encapsulate the salt grains within a network, lowering its interaction with water or trapping the chloride (Filippov et al., 2009). Chloride trapping into hydrocalumite in ordinary Portland cement has been reported (Haque and Kayyali, 1995). At high pH, hydrocalumite precipitates according to:

Leaching experiments, where oil-based cuttings were embedded into cement matrices, have shown that treating the cuttings with potassium phosphate decreases the amount of dissolved salt from 41.3 to 19.1%. In contrast, aluminium phosphate is more efficient for the stabilization of water-based cuttings (Filippov et al., 2009).

Methods for treating synthetic drill cuttings intended for landfill or for potential reuse as construction products have been screened (Al-Ansary and Al-Tabbaa, 2007). Two synthetic mixes were used, based on average concentrations of specific contaminates present in typical drill cuttings from the North Sea and the Red Sea areas. They contained a chloride content of 2.03% and 2.13% and a hydrocarbon content of 4.20% and 10.95%, respectively, so the mixes were denoted as low and high oil content mixes.

A number of conventional binders for stabilization and solidification were screened, including Portland cement, lime, and blast furnace slag, alongside some novel binders, such as microsilica and magnesium oxide. Despite differences in the hydrocarbon content in the synthetic cuttings under investigation, the measured mechanical properties of the samples with the same binder type and content were similar. Tests of the leachability of the samples showed a reduction of the amount leached into a stable non-reactive hazardous waste. Leaching tests are standardized by a European standard (CEN, 2002), although there are alternatives (Al-Ansary and Al-Tabbaa, 2007).

Experiments of the leachability of paraffins showed that lime-Portland cement binders showed the best performance, even at levels of 10% (Al-Ansary and Al-Tabbaa, 2007).

In offshore activities before 2000, the drill cuttings, are separated from other components of the drilling mud and then deposited in the vicinity of the platforms, but this has since been prohibited by legislation (Orszulik, 2008 and OSPAR, 2006).

This states that the cuttings must be transported to the shore, hence a new waste stream was generated. For example, in the UK, 40 kta⁻¹ of drilling cuts have to be disposed of, which means that technologies for disposing of this kind of wastes have had to be developed.

Oil-drill cuttings contain typically 50% OBM. The hydrocarbon content of these materials must be reduced to less than 1% before being discharged to landfill sites. Cleaned oil-drill cuttings could be used as filler materials, in particular for bituminous mixtures (Dhir et al., 2010). Several samples from different locations in the North Sea, were tested and proved to be either readily suitable for inclusion in pavement asphalt, or for the fabrication of bituminous mixtures after a minor adjustment of the method. Their performance was similar to limestone, and a few products were found to be even more effective than the original (Dhir et al., 2010).

Flocculation effluents of liquid phase oil-based drill cuttings may contain comparatively high concentrations of heavy metals, such as Cr⁶⁺. Environmental concerns can arise in the direct disposal of such liquids, so it is recommended that the flocculation effluent should be further treated before disposal.

Concentrations of Cr⁶⁺ of 5.26 gm⁻³ have been detected in representative untreated samples. Flocculation experiments using aluminum sulfate and sodium chloride as coagulant and flocculant, respectively, reduced this to 5.01 gm⁻³, which is highly unsatisfactory. Batch treatment with activated-carbon reduced the concentration of Cr⁶⁺ to 2.77 gm⁻³ (Ayotamuno et al., 2007).

Acid gas injection is a practical method to dispose of undesirable H₂S and CO₂ produced from natural gas. This technology allows sour gas reservoirs to be economically viable and provides an environmentally friendly disposal option.

Suitable formations for disposal must first be selected, for which it is necessary to examine the properties of the minerals in the rock formation. Injection should cause no significant changes in permeability (Bennion et al., 2004). Geochemical analysis of carbonate cores, previously subjected to acid gas core displacement tests by X-ray tomography, revealed changes of the porosity, which may increase the permeability (Vickerd et al., 2005).

Since carbon dioxide is a greenhouse gas, its capture is considered to be an important technology. The assessment of possible storage sites is needed for the technique to work.

A methodology has been developed for screening CO₂ storage fields, which was tested with data available in The Netherlands (Ramírez et al., 2010). The CO₂ storage capacities used in that study were estimated on the basis of data and results of previous studies performed by TNO (Schuppers et al., 2003).

Risk factors associated with CO₂ storage influence the suitability of a reservoir. If risk aspects are taken into account, a more realistic idea of the total storage potential for CO₂ is obtained.

The evaluation starts with assessing the total storage potential in a certain region (The Netherlands), and the storage costs and the efforts needed to manage potential risk are taken into account. A spreadsheet tool enables assessment of the criteria by evaluating the fields present in the database. The data have been weighted with a set of scores (Ramírez et al., 2010).

The study showed that 25% of the theoretical potential storage capacity in The Netherlands falls under the category of having the lowest scores regarding the effort needed to manage risk.

The slurry fracture injection (SFI) technique has been proposed as an alternative waste disposal method. This technique is environmentally secure and permanent, and does not leave any future liabilities that must be risk-evaluated or priced. An entire waste stream comprising the ground solids and the waste water can be injected into deep and hydraulically secure target strata. No contamination of drinking water formations should occur. The method could be used to clean and reclaim landfills, oil pits, and granular waste dumps (Uddin et al., 2009).

SFI feasibility can be measured by using a two-tier screening method to evaluate its feasibility and to identify suitable target zones. Parameters that have been used to decide about the feasibility of the method are summarized in Table 20.3.

Descriptive values are associated with these parameters, e.g., for impact on vegetation: reduction, unchanged, increase. Numerical scores are associated with the descriptions, and the scores flow into a decision tree.

This provides a simple and transparent decision aid for evaluating SFI sites. A multi-criterion evaluation is done, taking into account various engineering and environmental parameters.

A stringent environmental and process control monitoring program should accompany the period of planning and operation in order to ensure optimal environmental protection, waste containment, and regulatory health, safety, and environmental compliance. The necessary preconditions for the SFI technique are (Uddin et al., 2009):

The injection of the slurry is carried out in three phases, over a period of up to 12 h. Initially, a solids-free waste water is pumped to initiate or to propagate fractures. In the second phase, solid wastes are added in increasing amounts to the water. The content of the solids may reach 30% by volume. The maximum amount, of course, depends on the size and the nature of the solids and the geological characteristics of the formation. In the final phase pure water is pumped again in order to clean up the regions, i.e., the injection system, and the well itself (Uddin et al., 2009).

Waste chemicals generated by, for example, industrial plants, are often disposed of by injecting into disposal wells that penetrate subterranean zones (Reddy and Nguyen, 2005). Suitable subterranean zones for receiving such waste are separated by natural barriers from other zones that contain oil, gas, or water.

Unfortunately, many such chemicals are corrosive to the hydraulic cement in the wellbore. Also, any hydrogen sulfide or carbon dioxide gases that are generated or injected will form additional sources of degradation for the hydraulic cement.

Hydrogen sulfide corrodes the cement, and carbon dioxide reacts with calcium present in the cement at temperatures above 95°C (200°F). The high downhole temperatures accelerate the degradation process, meaning that the waste chemicals can leak into subterranean zones containing drinking water.

Sealing compositions are used to prevent this. For example, epoxy-based compositions can resist chemical degradation, and can be used to replace conventional hydraulic cements (Reddy and Nguyen, 2010). Epoxy-based compositions are highly resistant to chemical and thermal degradation, but their curing times are relatively short at 150°C (300°F) or higher (Reddy and Nguyen, 2005).

Alternative furan resins sealing compositions have therefore been developed. Furan resins in the so-called α-state are oligomers made from furfuryl alcohol and formaldehyde. When pumped down into the wellbore annulus, complete curing and crosslinking occurs.

The addition of a curing agent is necessary and a thinner or a diluent is added to adjust the viscosity. The curing of furan resins generally occurs by acid catalysis, c.f., Figure 20.3, so curing can be controlled via the adjustment of the pH of the system. For this reason, organic and inorganic acids are suitable curing agents, or for delayed curing, hydrolyzable esters additionally act as diluent. For pH adjustment, sodium bisulfate is used. Butyl acetate or furfuryl acetate are suitable hydrolyzable esters and diluents.

A coupling agent is added to enhance bonding to the interfaces, such as N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and N-β-(aminoethyl)-γ-aminopropyl trimethoxysilane (Reddy and Nguyen, 2010).

The sealant compositions also need a filler, such as low-density microspheres, i.e., hollow spheres of glass. To adjust the mechanical properties, plasticizers can be added. These include diethyl phthalate, butyl benzyl phthalate, and di-(2-ethylhexyl) phthalate.

The curing behavior of compositions based on either epoxy or furan was tested at 163°C (325°F). The results are shown in Figure 20.4.