Drilling fluids disposal

Drilling Fluid Disposal Conversion into Cements... 

Earlier on when we described the cutting action of the drill bit we learned about the drilling fluid or mud. The mud cools the bit and also removes the cuttings by carrying them up the hole outside the drill pipe. At the surface the mud runs over a number of moving screens, the shale shakers (Fig. 3.11) which remove the cutting for disposal. The fine particles which pass through the screens are then removed by desanders and desilters, usually hydrocyclones. 

Chemical additives for gas-based drilling fluids are limited to surfactants (qv), certain polymers, and occasionally salts such as sodium or potassium chloride. An aqueous solution of the additives is iajected iato the air or gas flow to generate a mist or foam. No additives are used ia dry air or gas drilling operations. Gas-based fluids are not recirculated and materials are added continuously. As the fluid exits the well, air or water vapor escapes to the atmosphere, gas and oil are burned, and water and formation soflds are collected into a pit for later disposal. Stable foams must be destabili2ed to separate the air from the Hquid phase for disposal. 

Sources of Toxicity. There are three contributing mechanisms of toxicity in drilling fluids, chemistry of mud mixing and treatment, storage/disposal practices, and drilled rock. The first group conventionally has been known the best because it includes products deliberately added to the system to build and maintain the rheology and stability of drilling fluids. 

However, dilution can lead to added costs of mud-treating materials such as weighting materials and other chemical additives. In addition, disposal of excess drilling fluid can create problems on offshore drilling projects. 

A new scheme for location management has developed whereby wastes are diverted to separate holding facilities according to the hazard imposed by the waste. Separate pits are created to hold rig washing and precipitation wastes, solid wastes and drilling fluids [225]. The waste is then reused, disposed on site, or hauled away for offsite treatment. The system reduces contamination of less hazardous materials with the more hazardous materials, thereby reducing disposal costs. 

The fluids from the reserve pit may be hauled away from location for disposal, reclaimed insitu, or pumped into the wellbore given a dryhole. The operator of the wellsite is responsible for the transportation offsite of the drilling fluids. The fluids may be considered hazardous in nature due to the toxic characteristics of most drilling and completion fluids. 

Methylglucosides also could find applications in water-based drilling fluids and have the potential to replace oil-based drilling fluids [801]. The use of such a drilling fluid could reduce the disposal of oil-contaminated drilling cuttings, minimize health and safety concerns, and minimize environmental effects. 

Major waste liquids arising from oil and gas production include produced water and drilling fluids and muds. These waste streams are handled and disposed of separately. 

Potential treatment and disposal methods for drilling fluids include (1) fluid ejection, (2) pit and solids encapsulation, (3) injection into safe formations, (4) removal to disposal sites off location, (5) incineration, (6) microorganism processing, and (7) distillation, liquid extraction, and chemical fixation [13]. 

This disposal method only applies to water-based drilling fluids. The fluids may be spread directly over adjacent agricultural or forest land after adjustment of pH and ion content. Treatment may include coagulation, flocculation, filtration, and pH adjustment before spreading. A major consideration is chloride ion content. With higher chlorides, some transport of the fluid to a better disposal site may be necessary. 

OGP (2003) Environmental Aspects of the Use and Disposal of Non Aqueous Drilling Fluids Associated with Offshore and Gas Operations, International Association of Oil and Gas Producers, London, pp. 114. 

Macdonald, R.W. (1982) An examination of metal inputs to the Southern Beaufort Sea by disposal of waste barite in drilling fluid. Ocean Manage., 8, 29-49. 

The process of drilling for crude oil and natural gas generates waste drilling fluids or muds, which are often disposed of by land farming. Most of these fluids are water based and contain barite and other metal salts. Thus barium may be introduced into soils as the result of land farming these slurried reserve pit wastes (Bates 1988). 

Drilling fluids and drill cuttings not removed as samples should be disposed of properly. These materials should not be placed into surface waters. They should be placed in stable configurations, with embankments and diversions provided to prevent contamination of runoff water where necessary. 

There are a few other precautions specific to the type of survey used. The effects of the induced seismic waves used in seismic surveys should be carefully analyzed, for potentially harmful effects on wildlife and nearby human structures. Also, when conducting radiometric surveys, drilling fluids and drill cuttings not removed as samples should be disposed of properly. These materials should not be placed into surface waters. They should be placed in stable configurations, with embankments and diversions provided to prevent contamination of runoff water where necessary. 

The oil originally used in oil-based drilling fluids was either crude or diesel oil. These oils have been largely replaced by refined mineral oils with aromatic contents below about 0.25 wt% (53). Alternative oil phases that have recently been introduced are poly(alphaolefins) (54) and esters derived from vegetable oils (55). These and other synthetic oils have been introduced in response to environmental pressures on the disposal of waste oil. 

The disposal of drilling fluid waste has become a major factor in the use of chemicals in water-based drilling fluids and in the use of oil-based drilling fluids because the dumping of waste from conventional (i.e., non-synthetic) oil-based fluids (drilling fluid and cuttings contaminated with oil from the fluid) is increasingly prohibited. 

Drilling fluid products that are to be disposed of from offshore platforms and landfill sites must be tested for their effects on animal and plant life. Components that have been identified as potentially toxic and hazardous to the environment are oil (diesel or mineral), heavy metals (Cr, Hg, Zn, Pb, etc.), and chlorides. 

Other methods of disposing of cuttings from oil-based drilling fluids have been investigated and include cuttings cleaning (using solvents, surfactant solutions, and supercritical fluids) and incineration (combus-... 

The combination of physical and chemical measurements previously described has the capability of giving a full description of the performance and composition of the drilling fluid. These measurements form the basis of a process-control approach to drilling fluids and the ability to correct for changes away from the optimal performance of the fluid by controlled additions of chemicals or changes in the solids control procedure. Such an approach should minimize the use of drilling fluid additives and the dilution-disposal of drilling fluids and should reduce the problems of waste disposal. 

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