Optimization of Drilling Mud Conditioning For Chemically-enhanced Centrifuging

Abstract Chemically - enhanced centrifuging, CEC, is a drill site process of environmental control of drilling mud. The process makes use of mud dewaterability in order to recycle the mud liquid phase and minimize waste volume. In this process, mud is chemically conditioned to enhance dewaterability -the ability of drilling fluid to release the free liquid phase. This paper introduces a simple method, a nine-point (9-P) experiment, to find the optimum dosages of coagulant, flocculent and dilution water that will minimize both the volume of dewatered solids and, the cost of chemicals. The experimental layout is based on the statistical theory of factorial analysis, so only nine measurements of dewaterability are needed to conclusively search for optimum treatment. The paper explains the design of the 9-P experiment and its interpretation with calculations of trends and tendency plots. Also presented is a feasibility evaluation of this method in terms of volume reduction compared to the treatment at random. The comparison shows a significant (1.8 and 2.4-fold) increase in efficiency of volume reduction, EVR and up to 3.7-fold reduction of chemical usage resulting from optimal selection of the most active flocculent Introduction The process of chemically--enhanced centrifuging, CEC, also know as mud dewatering, was introduced to drilling operations during the mid 1980's mostly in response to growing environmental regulations requiring minimization and recycling of drilling fluids (muds). In field operations, CEC is an addition to the drilling fluids processing systems (solids control) and is usually offered by a separate contractor or is integrated with mud engineering services. In environmentally-sensitive (zero-discharge) areas, CEC or annular downhole injection are the only alternatives to avoid high costs of drilling waste handling, transportation, and disposal. The importance of dewatering technology as an environmental control measure in drilling operations stems from a variety of its uses. In principle, CEC removes water from sludge so that the dewatered-sludge volume is minimized (sludge densification). Alternatively, the process is viewed as the removal of solids from water suspensions (water clarification). Finally, CEC can be considered a recovery process in which an expensive liquid phase is recovered from waste (liquid phase recycling). In oil well drilling operations, CEC is used in all three applications. In reserve pit closures, water must to be removed from the earthen pit to minimize the volume of sludge for on-site burial (sludge densification) [1,2]. In the processing of the well-site's wastewaters ("gray" water, deck drainage, stormwater, and run-off water), CEC is used for water clarification [3]. The third oilfield application of CEC is continuous dewatering of active drilling mud [4,5,6]. In this application, the excess volume of drilling mud, caused by the rheology-control dilutions, which are used to maintain mud properties required for drilling, is dewatered in order to recover its liquid phase for use in these dilutions. The CEC process consists of three stages: chemical conditioning; forced settling; and mechanical expression. Chemical conditioning destabilizes the continuous suspension of fine solids in drilling mud and converts this suspension to a mixture of solid agglomerates (flocs, flocculates) and the free liquid phase.