Recovery of Oil from Drilled Cuttings by Liquefied Gas Extraction

Abstract

It has long been accepted that non-aqueous invert emulsion drilling fluids provide improved drilling performance compared to traditional water-based systems. Use of diesel, mineral oil, and more recently, synthetic materials such as olefins and paraffins as base fluids has gained global acceptance. However, the disposal of these materials and associated drill cuttings can generate environmental concerns. The capability to remove oil or synthetic oil from the cuttings before disposal can significantly reduce the long-term environmental effects of disposal. In addition, effective recovery of costly synthetic fluids could improve the overall economics of drilling. This paper summarizes research efforts into development of a technique that uses liquefied hydrocarbon gases as solvents to extract oil from cuttings. The laboratory data presented shows that a wide variety of fluids can be efficiently recovered from cuttings. Residual oil on cuttings levels can be reduced to concentrations exceeding the standards typically required for disposal or discharge, with no thermal energy requirements and recycling of the solvent phase and recovered fluid. Risk assessments indicate that the technique can be safely applied at both onshore and offshore operations. Introduction Invert emulsion drilling fluids, also known as nonaqueous fluids (NAF) or oil-based muds (OBM), were introduced in the 1960s. These fluids are usually preferred over aqueous (water-based) drilling fluids because they improve drilling performance, particularly with regard to drilling rate, hole stability, thermal stability, and lubricity. Recent advances in water-based fluids1 have gone a long way to close this performance gap, but in many cases, invert emulsion fluids are still the preferred option. Invert emulsion drilling operations generate drilled cuttings mixed with invert emulsion fluids. Typically, drilled cuttings contain 5–15% (by weight) of the base fluid used to build the invert emulsion fluid. Typical wells generate 1000–2000 metric tonnes (MT) of cuttings per well. Therefore, a typical well may dispose of as much as 300 MT of base fluid. The disposal of drilled cuttings associated with invert emulsion fluid can represent a potential environmental concern, especially in offshore operations where drilled cuttings have been traditionally disposed of in the sea. Other factors, including the tightening of environmental regulations, shipment of cuttings to shore, and generation of invert emulsion fluid cuttings in land operations can also add to environmental concerns regarding the disposal of cuttings on land. Because of these concerns regarding the environmental impact of disposal of invert emulsion fluids cuttings, a number of technologies have been developed that subsequently led to the technology described in this paper. Evolution of Invert Emulsion Fluids The first invert emulsion fluids were created with diesel oils, primarily because of the low cost and widespread availability of diesel. In many parts of the world, diesel fluids are still successfully used. However, in the early 1980s, many operators became concerned about the occupational health risks associated with diesel-based fluids and consequently requested fluids based on oils with a lower aromatic content and flash point. As a result, mineral oils became a common invert emulsion base fluid, even though a higher degree of refining made them more expensive than diesel. In many areas, operators have changed to mineral oils, especially for land-based and zero-discharge offshore activities.

Treatment of Hydrocarbon-Based Drilling Waste Using Supercritical Carbon Dioxide

“…Visual observation of the two chromatograms shows a detector response with similar peaks. This result would suggest that the hydrocarbon is unchanged by the SFE process and corroborates the results of several previous studies 3, [13][14][15] . This result suggests that there is a potential for the hydrocarbon to be collected from the SFE waste treatment process and be reused in future drilling operations.…”

“…More recently, a SFE study published by Seaton and Hall showed that both supercritical propane and butane were suitable for the removal of synthetic, diesel and mineral oil hydrocarbons from drill cuttings 13 . Early tests in the study encountered difficulty with even distribution of the supercritical fluids in the waste, or 'channeling'.…”

Treatment of Non-Aqueous Drilling Waste Using Supercritical Carbon Dioxide

“…The appearance of the solids after extraction (large chunks) indicates that the mixing was not sufficient to maintain constant, even contact between the drilling waste and the SC CO 2 , similar to the aforementioned channeling problems documented by Seaton and Hall (9) . The appearance of the solids after extraction (large chunks) indicates that the mixing was not sufficient to maintain constant, even contact between the drilling waste and the SC CO 2 , similar to the aforementioned channeling problems documented by Seaton and Hall (9) .…”

“…More recently, a study completed by Seaton and Hall showed that supercritical propane and butane were suitable for the removal of both synthetic and natural oil from drilling waste (9) . Their initial testing encountered problems with channeling, or uneven distribution of supercritical fluid, which were later resolved using ceramic pellets for mixing.…”

CO2-Repurification Microemulsion Detergent for Oil-Based Slurry Cleaning

“…Methods include removal of petroleum hydrocarbons using organic solvents (hexane, heptane, and toluene) as the main extractant, 5 supercritical carbon dioxide elution, 6 and liquid organic compound gas extraction for cleaning oily solids. 7 However, these technologies often require expensive equipment to achieve and maintain the pressure of the extraction medium to reach a supercritical state, as well as cost and safety considerations, which limit their use in the oil and gas industry. In order to reduce process energy consumption, the surfactant cleaning method is simple and safe to operate.…”