Deposition of paraffins and asphaltenes in the near well bore region has always been one of the most studied cause of production decline especially in brown fields. Pumping heated fluids, inhibitor pumping, or mechanical methods of clean out using coiled tubing jetting or jointed pipes are some of the industry prevalent methods of countering this issue. But these methods are both cost and time consuming with short lasting results. With industry constantly marching towards the production of more and more ‘difficult oil’ it has become the need of hour to devise and deploy more cost and time efficient methods to mitigate the problem. The paper highlights the application of In-Situ Heat generation methodology and details the execution process used to mitigate the near wellbore wax deposition in field X in western part of India. Field X in India has been developed as an onshore field wherein wells are drilled in shallow reservoir. To support the oil production, some wells are produced using Artificial Lift techniques like PCP. Crude of the reservoir is high in wax content with pour point at 60 °C which is very close to reservoir temperature (~65 °C) resulting in high wax deposition against screens & near wellbore. The wax dissolution temperature is well above the reservoir temperature, due to which any effective remedial treatment necessitates higher temperature generation for dissolution/inhibition of wax problems. In-Situ Heat generation methodology is based on the concept of down-hole heat generation by exothermic chemical reactions. The paper details the operational challenges observed while conducting the operation in both PCP and non-PCP wells and various measures taken to mitigate the same. Steps in developing this system and using it in the field are documented, and the challenges encountered, lessons learnt and recommendations for future application of the system are described.

Waterflood is most commonly used secondary recovery mechanism in conventional sanstone reservoirs worldwide. Waterflooding assists in pressure maintenance and increases the field estimated ultimate recovery (EUR). Conformance in water injector wells plays an important role during waterflooding of a reservoir. Better conformance results in improved vertical sweep efficiency leading to higher recovery. Continuous injection of fluids into the reservoir at higher rates may create channels for preferential flow. Zones of higher permeability, leading to higher injectivity in selective zones, can also exist because of various lithological conditions and rock structures comprising of naturally occurring fractures or fissures. For injection wells, the entry of fluids into a set of perforations is governed by the quality of the perforations and the permeability of the formation at that depth. Preferential flow of injected fluids into selective pay intervals results in diminished overall sweep efficiency. (J. Vasquez, et.al., 2008). This paper discusses the use of thermally activated gels from polyacrylamides and metal chelates applied for selective reservoir matrix permeability reduction in an injector well. A low concentration, low viscosity delayed crosslinker gel system employing partially hydrolyzed polyacrylamide (PHPA) exhibiting 12-14% degree of hydrolysis level with chromium acetate as crosslinker offering delayed gelation time was used to selectively isolate one of the payzones. A non-profile retrievable (NPR) plug was installed to isolate the target interval from the rest of the pay zones to enable selective treatment of the interval using coiled tubing (CT). The fluid was customized to minimize CT friction while ensuring that the rheological properties of the fluid in the reservoir would achieve the desired diversion and allow delayed gel crosslinking mechanism assuring avoiding of gel crosslinking in CT while pumping in progress. Denser brine relative to the delayed gel density was spotted above the NPR plug to avoid gel settling on the plug for easy retrieval of the plug post-treatment. Injectivity was measured and subsequently, the treatment was placed as per design while constantly monitoring the pressures so as to qualitatively determine the effectiveness of the treatment placement. The treatment resulted in significant alteration in injectivity of the targeted zone. Post-treatment production logs confirmed an improvement in the injection conformance. Later, the zone was isolated and the bottommost zones were selectively stimulated enhancing the injection and thus improving sweep efficiency. Since the crosslinked gel system is not prone to any disintegration when in contact with acidic interventions, the treatment ensures a superior longevity of the conformance control when compared to other conventional diversion or zonal shut-off treatments. The success of the treatment substantiates that the CT deployed low viscosity, low concentration delayed crosslinked gel system application can be successfully extended to selective water shut-off applications in producer wells. The injector profile modification treatment executed offered a comprehensive solution to conformance issues enhancing volumetric sweep efficiency, pressure maintenance across depleted sands and avoiding further water cycling in producer wells.

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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".

Mangala Field in Rajasthan, India was discovered in January 2004 and began production in August 2009. The main reservoir unit is Fatehgarh Formation, consisting of interbedded sands and shales. Upper Fatehgarh sand (FM-1) has almost 50 % of field STOIIP. It is a fluvial channel sand with excellent reservoir characteristics (average porosity ~ 25% and average permeability of more than 3000 md). Crude is waxy and wax dropout temperature is close to reservoir temperature. This reservoir is being developed by an inverted 9-spot hot waterflood, but a subsequent chemical flood EOR (polymer + ASP) is planned. Currently, an inverted 5-spot pilot program is being carried out to assess the effectiveness of a chemical flood. Initial injection profiling data suggested that vertical conformance was poor, possibly due to poor injection water quality and wax dropout, but it was envisaged that selective chemical treatment of the channel sands would help in improving it. Initially, chemical assisted diversion techniques were applied in two wells which resulted in substantial reduction in ITHP with negligible improvement in conformance. Thereafter, a coiled tubing and straddle packer system was used to ensure correct placement of a series of chemicals targeting different damage mechanisms i.e. wax deposition and scaling issues. Stimulation techniques included increasing the injection temperature of the water for wellbore heatup and wax dissolution, spotting and soaking of surfactants for dissolution of residual wax, followed by pin point injection of 15% HCL for dissolution of scales. Post stimulation injection logs showed an excellent achievement of conformance. An improved surface setup in the EOR pad (water heater, improved filter design) has helped in maintaining the injectivity over a longer time period. The lessons learned from this stimulation technique would prove to be critical for the FM1 sand, where improvement in vertical conformance would result in significantly higher recovery.