Waste Water Treatment by Chemical Coagulation Method-Increasing Output and Reducing Environmental Impact

Abstract

Cairn, Oil & Gas vertical of Vedanta Limited operates ~27 per cent of India’s domestic crude oil production processing upto 1MM bbls of produced fluid. Management and disposal of produced water after stimulation and work over/completion is one of the most challenging problems to sustain productivity without upsetting the surface facility. In order to prevent facility upset, the initial flow back of spent acid is taken into lined pit to allow for longer residence time and effective separation before treatment. Facility has earlier encountered emulsion formation issues for pH less than 6 and iron content more than 50 ppm. Therefore it was imperative that flowback fluid has to be treated to achieve acceptable water quality prior to disposal and maximize treatment volume at low treatment cost. During the first phase of the waste water treatment, Electrocoagulation (EC) method was implemented for decreasing waste water footprint. This method although successful in treating waste water in terms of quality, could not effectively manage high volume of generated waste water. Operation of EC unit also consumed high quantities of energy sources (like Diesel/Electricity) causing higher OPEX and larger carbon footprint of the project. The objective of this paper is to discuss the approach of using innovative method of Chemical Coagulation in place of Electrocoagulation for treating waste water to increase treatment volume in a sustainable manner, along with reduction in OPEX while using minimal additional CAPEX. A series of laboratory experiments were conducted among various chemical coagulants, and PAC (Poly Aluminum chloride) was selected on the basis of effectiveness and operational feasibility. PAC works by coagulation of effluent particles present in waste water. Efficiency of the process was further increased by addition of flocculants (like Anionic Polymer) with coagulants, this led to reduction in required retention time for effluent settling and effective separation of solid waste. Post success of laboratory tests, minor modifications in plant design were implemented, and multiple field tests were conducted by varying dosing concentrations of PAC and Polymer. Also retention time was varied by changing chemical dosing locations within the plant. After successful completion of field trials for Chemical Coagulation method, the project was implemented on full scale. With minimal additional CAPEX, nearly threefold increase in treatment volume with 50% reduction in OPEX has been achieved. Chemical method has also contributed in reducing environmental impact by not generating additional solid byproducts and by decreasing carbon footprint of project. This change in operating method of water treatment plant from EC to Chemical Coagulation has helped to maximize the output of plant while decreasing OPEX and environmental impact. Success of the pilot project opened avenues of using more innovative technologies for efficient disposal of solid waste from the plant and paving the way towards a "Zero Discharge plant".

Reuse of Flowback Water from Hydraulic Fracturing for Drilling Mud Preparation and Secondary Hydrocarbon Recovery

“…Dastgheib et al [62] have verified coagulants like ferric chloride (FeCl 3 ) and aluminum sulphate (Al 2 (SO 4 ) 3 ) by jar tests. Agarwal et al [63] found poly aluminium chloride (PAC) to be suitable coagulant for flowback fluid. Hosny et al [64] proved that chitosan from shrimp shells mixed with carboxy methyl cellulose as a coagulant allow to remove 99% of oil from oily produced water.…”