Summary Oily cuttings and waste fluid are byproducts of oil-based drilling muds. In such difficult drilling environments as the Gulf of Mexico, where oil-based fluids often are preferred, personnel safety, environmental, and economic concerns are exacerbated by the necessity to transport these cuttings and fluids to shore for disposal. This paper describes a process for on-site preparation and subsequent disposal of a slurry of cuttings by annular pumping. The disposal includes all cuttings and waste oil mud generated during drilling with oil-based fluids. Wastes are displaced down a casing annulus and into permeable zones below the surface casing setting depth. Descriptions of environmental and safety problems arising from onshore disposal, benefits of annular pumping, and equipment used for slurry preparation and pumping are described. This technique eliminates the need for platform cuttings storage, cuttings transportation to shore, and the environmental effects of onshore disposal. Introduction U.S. governmental regulations currently prohibit the discharge of free oil into the Gulf of Mexico during drilling operations. This ban on oil discharges has resulted in the necessity for operators to transport the waste mud and cuttings generated during drilling with an oil-based mud to an appropriate onshore waste treatment or disposal facility or to switch to exotic and sometimes unproved water-based systems. Although these water-based mud systems have not always failed, they have not proved to be fully acceptable alternatives to the oil-based systems they have displaced. Both economic and environmental considerations have dictated that more wells be drilled from fewer surface installations. As a result, more highly deviated and often horizontal wellbores have been drilled through the young, troublesome, water-sensitive shales that have plagued gulf drilling operations in the past.1 Successful drilling under these conditions in many areas of the gulf2 and other offshore environments3 requires the use of an oil-based fluid. Consequently, the implementation of an environmentally acceptable disposal method for oily cuttings and mud at the drillsite would reduce drilling costs and minimize the potential environmental exposure that would result from transport of this material to shore for disposal. Thus, a technique for converting the cuttings and mud into a slurry for slurry disposal by pumping it down the annulus of a well was developed. As this paper describes, annular pumping is the one-time displacement of drilling fluids and solids into a nonproductive, permeable zone (primarily sandstone) for disposal. Environmental Background The U.S. Environmental Protection Agency (EPA) regulates discharges from offshore oil and gas production facilities under the General National Pollutant Discharge Elimination System (NPDES) Permit No. GMG280000.4 These discharges are defined in the Oil and Gas Point Source Category of Title 40 of the U.S. Code of Federal Regulations (40 CFR 435). The permit allows the discharge of water-based drilling fluids and cuttings to the gulf, as long as the discharge does not result in a sheen on the ocean's surface (the so-called "no-free-oil restriction"). Additionally, the suspended particulate phase of the drilling fluid must pass a 96-hour toxicity test (LC50>30,000 ppm). Permit No. GMG280000 expired at midnight, Eastern Standard Time, July 1, 1991; however, the EPA published proposed Permit No. GMG2900005 for the western Gulf of Mexico. This permit places comparable restrictions on oil-based mud use and will, when finalized, replace the expired permit. As a result of these regulations, oil-based drilling fluids and the cuttings generated by drilling with these fluids cannot be discharged into the Gulf of Mexico. Consequently, the use of an oil-based mud system called for waste disposal in a commercial, onshore, nonhazardous oilfield waste (NOW)disposal location, where the waste is either buried or land-farmed. Historically, movement of drilling wastes to a NOW facility was not adequately tracked, nor was waste disposal well documented. Common industry practice included trucking mud and cuttings from offshore and onshore locations to the commercial facility. Often, the only records of these transactions were transportation and disposal invoices. Although these operations were conducted in accordance with applicable regulations, because non-NOW material was deposited at these sites, certain sites have been classified by the U.S. EPA as Comprehensive Environmental Response, Compensation, and Liability Act Superfund Sites. Remediation costs are shared by all who used the site for disposal regardless of the type of wastes taken to the site. The prohibition on the discharge of oil-based waste has caused a re-evaluation of the economic, safety, and environmental consequences of a "no discharge"offshore drilling operation. The associated expense, employee exposure to transfer operations, potential oil-spill cleanup exposure, and possible future liability of commercial NOW sites all have combined to create a need for an onsite disposal option. Because oil-based drilling-fluid systems have been the operational fluid of choice for drilling in the Gulf of Mexico, new procedures and techniques that would continue to allow the use of these fluids in the offshore environment have been sought. Oil-based-mud cuttings cleaning systems* have been developed, patented, and field tested. These systems, although operationally and environmentally sound, proved too slow to provide real-time treatment of generated waste and proved to be comparatively expensive for the offshore environment. Several efforts have been reported6–11to develop technologies that would render oil-based-mud waste suitable for offshore discharge. Cuttings washers, incinerators, and solvent-extraction systems all failed to produce environmentally acceptable effluents, were too expensive to use, or were considered unsafe for offshore application. Consequently, when the need for oil-based muds was identified, many operators relied on the on-site collection of the oily cuttings and mud in boxes. These boxes then were transported to shore by dedicated work boats, and the contents were buried in commercial NOW disposal facilities. Annular pumping for waste-water disposal has been used in several situations. In one application, drilled cuttings are recycled for use as road-building material and the water used to clean the cuttings is pumped into a permeable zone below the surface casing.12,13 In many areas, produced water routinely is pumped into production zones for EOR purposes.

Summary The use of mobile, chemically enhanced centrifugation dewatering systems toprocess liquid waste from two deep exploratory wells in Kern County, CA, saved $136,900 in waste-disposal costs. Liquid waste in the wells was reduced by 45%. This paper tracks daily costs and chemical usage for each well to isolate keycost factors. Introduction The use of different types of dewatering technology to process effluent fromvarious industries has been well documented. others have reported on the use ofa centralized facility to process drilling waste transported from a number ofdrilling sites to the facility, hut the application of the technology at anactive drilling location has been limited by the complexity of dewatering. Theuse of the technology as an on-line addition to the rig's solids controlequipment has been suggested, but the results of such on-line processing havenot been extensively reported in the literature. This paper reviews the use ofone such dewatering paper reviews the use of one such dewatering technique, chemically enhanced centrifugation, at two active drilling locations. Chemically enhanced centrifugation uses chemical coagulants and flocculants toachieve fine-particle flocculation. The flocculated solids are then separatedfrom the waste stream with a high-speed centrifuge. This solids-separationtechnique differs from conventional "closed-loop" mud systems in oneimportant way: conventional closedloop systems rely on additionalsolidsprocessing equipment, such as "microclones" (small-diameterhydrocyclones), and traditional centrifuges to separate water and solids fromthe waste stream. Processing in this manner generally fails because theadditional solids-processing equipment cannot remove extremely fine particlesfrom the waste stream. When the particles from the waste stream. When therecovered water is returned to the mud system, fine solids are ala returned tothe mud. Continued reuse of the recovered water eventually results in afine-particle accumulation in the mud system that can be corrected only throughmassive dilution. Thus, the objective of waste-volume reduction is defeated or, at least, severely compromised. Chemically enhanced centrifugation, however, removes fine solids by treatment with chemical coagulants and flocculants. In July 1988, Arco Oil and Gas Co.'s Western Dist. began field testing of twodewatering units that used chemically enhanced centrifugation to process liquiddrilling waste. Both units were mobile in the sense that the component partscould be loaded onto two trailer trucks and transported to the drillinglocation for assembly. Both units were comparable in design and operation andwere furnished by the same service company. Before the units were selected, alist of checkpoints that were considered key to the successful operation ofsuch a unit was prepared (see Table 1). Available units were prepared (see Table 1). Available units were compared on the basis of a physical examinationfollowing this list. The unit with the best score was selected for the tests. Operational considerations limited the size of the reserve pit at bothfield-trial locations. The dewatering units were used to create aminimum-discharge (closed-loop) solids-control system. Because the cost ofliquid-waste disposal was $10.85/bbl, the plan was to send all the effluents tothe dewatering unit for processing. The recovered water would be returned asneeded to the mud system, and the solids separated by the centrifuge would bedischarged to the reserve pit. Because this recovered water was to be pit. Because this recovered water was to be reused in the mud system, asuspended-solids content of less than 500 mg/L and a residual-polymer contentof less than 0.1 lbm/bbl in the recovered water were dewatering goals. Thepurpose of these field trials was to assess the ability of the dewatering unitto achieve water-clarity goals for less than $10.85/bbl. This assessment wouldprovide one means of evaluating the economic viability of thisminimum-discharge solids-control system. Well Background Data The Mettler No. 1 was drilled in the Tejon (North) field, Kern County, CA. The dewatering test began July 26 and was completed Oct. 24. The dewateringunit was on location 96 days. Fig. 1 is a schematic of the well's hole size andcasing programs. The Arco-Texaco No. 801 was drilled in the Midway Sunsetfield, Kern County. The dewatering test began Aug. 18 and was completed Dec.20. Difficulty in setting cement plugs for directional control caused the timeplugs for directional control caused the time on location to be significantlylonger than planned (125 days). Fig. 2 is a schematic planned (125 days). Fig.2 is a schematic of the well's hole size and casing programs. JPT P. 730

The need for a reliable, quant.it.at.ive analyt.ical method for the det.erminat.ion of the partially hydrolyzed polyacrylamide (PHPA) polymer content. of drilling mud and ot.her wat.er-base fluids has been evident. for some t.ime. Previous methods have been based on eit.her t.he predpitat.ion of the anionic PHPA molecule or alkaline hydmlysis of t.he amide nit.rogen to form ammonia. All these met.hods are semiquant.it.at.ive det.erminations and are subject to a wide variety of int.erferences. Anot.her severe limit.ation, in t.he case of drilling fluids, is that a port.ion of the mud filtrat.e is used for analysis, The free polymer cont.ent of t.he filt.rat.e is rarely, if ever, the same as t.he unfilt.ered liquid phase of t.he whole mud.The method described in t.his paper is truly quantit.ative and is an absolute rather t.hen an empirical met hod. It is based on the t.ot.al oxidation of all organic material in a sample of t.he liquid phase of a wat.er-base dJ"illing fluid. The amide nit.rogen in t.he polymer molecule forms ammonium ions during the digest.ion and oxidat.ion process.These ammonium ions are then measured with an ammonia gas·sensing elect.rode afler conversion to ammonia by means of a simple pH adjustment.In addition, a sampling technique has been developed which enables the analyst t.o obt.ain a solidl'·free port.ion of the liquid phase of a drilling mud sample without. filtering the liquid t.hrough t.he mud filter cake. Thus, t.he met.hod assures measurement. of t.he available free polymer cont.ent of the fluid phase of t.he whole mud.The met.hod described is ideally suit.ed t.o t.he det.ermination of t.he PHPA cont.ent. of any aqueous solutions including t.hose encountered in wastewater treatment. and sludge dewat.ering operat.ions. The results of both laborat.ory and field evaluations of t.he method are present.ed.References and illust.rat.ions at. end of paper. 415

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractLoss of synthetic-based mud (SBM) on drilled cuttings discharged offshore can add considerably to the drilling fluid cost. In addition, offshore environmental regulations are becoming increasingly strict, causing discharge of SBM to be severely curtailed. To reduce the loss and discharge of SBM, a new mud recovery technology -Centrifugal Drying -was tested as an enhancement to conventional solids control technology on four development wells in the Gulf of Mexico.Centrifugal Dryers, sometimes called rotating shakers, remove fluid from the cuttings by use of a spinning, screened basket arrangement which imparts a Centrifugal force on the order of 100 G on the cuttings. Cuttings discharged from the shakers are transferred to the Dryer's inlet pipe and are fed by gravity to the distribution cone and support disc. The cone removes the cuttings from the pipe and accelerates and spreads them evenly over the inner surface of the conical screen. Cuttings are held to the screen by Centrifugal force and moved to the exit port via vibratory motion or a sweeper, while the drilling fluid is forced through the screen and recovered.In the field tests, the conventional solids control equipment left a residue of synthetic fluid on the cuttings (SOC) of 10 to 15% by weight, whereas the Centrifugal Dryer was generally found to reduce SOC to less than 5% by weight (Fig. 1). Furthermore, the cuttings discharged from the unit dispersed readily and produced no visible sheen when released into the sea water under the cuttings discharge line. By reducing the volume of synthetic discharged, a savings of about $100,000 in mud cost was realized over the life of the project (4 wells).

Quantifying total iron in brine is critical in order to mitigate its unfavorable effects. An API-sponsored work group has developed a robust field method for determining the levels of iron contamination in all oilfield completion brine, including zinc-based brine. This colorimetric, semi-quantitative method is based on chemistry involving acidification, peroxide oxidation, and thiocyanate complex formation. The iron content is quantified by comparing the intensity of the resulting colored complexes to standards. Using newly-developed, commercially available vacu-ampoule test kits (Figure 1), this assay is quick and particularly user-friendly, and it is easily implemented in the field. It is anticipated that this method will be incorporated into the API Recommended Practice 13J, Testing of Heavy Brine. Introduction Accumulation of iron salts in a brine completion fluid can lead to significant formation damage and greatly affect the productivity of a well. In addition, iron can cause cross-linking and gelling of polymers and increase the stabilization of crude/brine emulsions. Quantifying total iron in brine is critical in order to mitigate its effects. Iron contamination in oilfield brine typically is a result of corrosion processes of iron-containing metallic components and equipment. This can occur in both aerobic and anaerobic environments, either electrochemically or microbiologically-induced. In the corrosion process, metallic iron is first converted to Fe+2 [the ferrous cationic species] with the loss of two electrons. Fe+2 can be converted to Fe3 [the ferric cationic species] with the loss of an additional electron. The electron acceptor depends on the environment and the configuration of the system. Generally, Fe+2 salts are water soluble, and Fe+3 salts are water insoluble. Background In 1994, Subcommittee 13 Task Group 6 convened a Work Group to develop a field-friendly assay for iron quantification in heavy brine that would be effective across the full range of halide and organic brine. Inductively Coupled Plasma (ICP) and Atomic Absorption (AA) techniques with matrix matching work well, but these methods require expensive equipment, high levels of chemical expertise, large and controlled physical settings, and extensive laboratory manipulation. Neither of these techniques is readily amenable to field application. Prior to the development of the new technique, the Work Group evaluated a number of alternative methods. Many of these are familiar to the oilfield, water, and wastewater industries, but do not work well in brine containing even minor levels of zinc bromide. This includes the standard self-filling ampoules (1,10-phenanthroline chemistry) iron assay commonly used for low-density brine and wastewater analyses. Other techniques considered, including reactive colorimetric strips, were shown to have poor accuracy below 75 ppm iron, to have a high degree of sensitivity to moisture and temperature, or to require development with strong acids. A proposed spot test showed poor reproducibility in round robin exercises. The limitations detailed above were addressed using a spectrophotometric technique. The sample was acidified, oxidized with peroxide, and complexed with thiocyanate. A quantitative result was determined using a hand-held single-wavelength spectrophotometer with blanks and a calibration curve. Although the technique addressed the zinc issue, the extensive sample, standard, and reagent preparation made this technique difficult for field applications.