Drill cuttings are the earth, rock and other solid materials generated during the rotary drilling of subterranean wells. The drill cuttings are removed from beneath the drill bit by a stream of drilling fluid that suspends the solids and carries the solids to the surface. On the surface, the drill cuttings are separated from the drilling fluid in a drilling cuttings separator or shaker and the drill cuttings are collected at the drill site for subsequent treatment.
Traditional oleaginous drilling fluids, also known as oil-based drilling fluids or invert emulsion drilling fluids (if they contain an internal non-oleaginous phase), may be harmful to marine life due to the presence of aromatic hydrocarbons in the diesel fuel or other similar petroleum fractions used as the continuous phase. The development of low-toxicity mineral oil-based drilling fluids—with very low fractions of aromatic compounds—allayed much, but not all, of the concern over acute toxicity effects on marine flora and fauna. However, discharge of mud-laden cuttings still produces a mound of cuttings on the ocean floor that may smother any marine life that resides on the seabed.
Development of synthetic-based drilling fluids as alternatives to conventional oil-based drilling fluids in offshore operations was precipitated by residual toxicity and biodegradability concerns. These developments focused on the fate and effects of oil-coated drilled cuttings discharged into the sea, as well as worker safety. For onshore applications, cuttings disposal is also of importance. However, since the drilled cuttings are disposed of on land, the environmental issues focus primarily on subsequent usability of the land and contamination of ground water. Although the advent of synthetic-based fluids has greatly improved the environmental acceptability of non-aqueous drilling fluids both offshore and onshore, current synthetic-based fluid formulations still present problems for direct land treatment of oil-coated cuttings resulting from onshore operations. The concerns with pollution of soil and groundwater by synthetic based fluids and oil-based fluids have led to increasingly strict government regulations.
Oily drill cuttings can have severe impacts on their receiving environment and should be cleaned or treated to minimize their environmental impact and the operator's long term liability. The primary purpose of each of these methods is to somehow destroy or remove the drilling fluid residue from the earth solids. In addition to the above mentioned method of land treatment (spreading and farming), there is a litany of other ways to treat oil-coated cuttings from drilling operations. These include landfill disposal; bio-remediation; stabilization/solidification (briquetting, fixation with silicates or fly ash); extraction or washing (oil, detergents, and solvents); and thermal treatment (incineration and distillation, including thermal desorption and hammer mill). The treatment of drill cuttings is the subject of a number of patent applications and literature disclosures that include U.S. Pat. Nos. 6,187,581; 6,020,185; 5,720,130; 6,153,017; 5,120,160; 5,545,801; 4,696,353; 4,725,362; 4,942,929; 5,132,025. These patents describe various methods of treating oily drill cuttings including incineration; reinjection of the slurrified cuttings into another subterranean formation; chemical washing and landfill disposal; and other methods. As noted above, the primary purpose of each of these methods is to somehow destroy or remove the drilling fluid's residue from the earth solids.
Despite considerable research conducted in the area of drill cuttings disposal, there remains an unmet need for a clean, inexpensive and environmentally friendly drilling fluid and method of treating the drill cuttings such that they produce an end product that may have a beneficial use.