Optimization of Drilling Mud Conditioning For Chemically Enhanced Centrifuging

Abstract

Abstract Chemically-enhanced centrifuging, CEC, is a drill site environmental control process for drilling mud. The process makes use of mud dewaterability for recycling the mud liquid phase and minimizing volume of the waste mud discharge. In this process, mud is chemically conditioned to enhance dewaterability- the ability of drilling fluid to release its liquid phase. This paper introduces a simple method, the nine-point (9-P) experiment, for finding optimum chemical conditioning (i.e., combination of dilution water, coagulant and flocculent) that would maximize the mud volume reduction and minimize the cost of chemicals. The 9-P experiment is based on the statistical theory of factorial analysis and requires only nine tests to find optimum treatment. The paper explains how to design the experiment and analyse its results. Also presented is a comparison of 9-P (in terms of volume reduction) with the conventional trial-and-error approach. The comparison shows a significant, from 1.78 to 2.35 - fold, increase of the volume reduction efficiency, EV R, 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 known as mud dewatering was introduced to drilling operations during the mid 1980s mostly in response to growing environmental regulations requiring minimization and recycling of drilling fluids (muds). In field operations, CEC is an extension of the drilling fluid processing system (solids control) and is either offered by a separate contractor or integrated with the complete mud engineering service. In environmentally-sensitive (zero-discharge) areas, the CEC or downhole injection technologies are the only alternatives to off-site disposal involving high cost 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 oilwell drilling operations, CEC is used in all these applications. In the reserve pit closures, water must be removed from sludge in the earthen mud pit to minimize the volume of sludge for onsite burial (sludge densification)(1,2). In the processing of the well site's wastewater ("gray" water, deck drainage, stormwater and run-off water), CEC is used for water clarification(3). The third oilfield application of CEC is a continuous dewatering of active drilling mud(4,5,6). In this application, the excess volume of drilling mud (resulting from solids control dilutions) is dewatered and the recovered liquid phase is used for further 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. Then, this mixture is pumped into the centrifuge where the remaining two stages take place.