Performance Comparison of Control Strategies for Plant-Wide Produced Water Treatment

Offshore produced water treatment (PWT) accounts for cleaning the largest waste stream in the offshore oil and gas industry. If this separation process is not properly executed, large amounts of oil are often directly discharged into the ocean. This work extends two grey-box models of a three-phase gravity separator and a deoiling hydrocyclone, and combines them into a single plant-wide model for testing PWT control solutions in a typical process configuration. In simulations, three known control solutions—proportional-integral-derivative (PID) control, H∞ control, and model predictive control (MPC)—are compared on the combined model to evaluate the separation performance. The results of the simulations clearly show what performance metrics each controller excels at, such as valve wear, oil discharge, oil-in-water (OiW) concentration variance, and constraint violations. The work incentivizes future control to be based on operational policy, such as defining boundary constraints and weights on oil discharge, rather than maintaining conventional intermediate performance metrics, such as water level in the separation and pressure drop ratio (PDR) over the hydrocyclone.

Recent advances, influencing factors, and future research prospects using photocatalytic process for produced water treatment

Oilfield-produced water is the primary by-product generated during oil and gas extraction operations. Oilfield-produced water is often severely toxic and poses substantial health, safety, and environmental issues; adequate treatment technologies must bring these streams to a quality level. Photocatalysis is a photochemical catalytic reaction that is a highly promising tool for environmental remediation due to its efficiency in mineralizing persistent and potentially toxic contaminants. However, there is limited understanding of its application to treating oilfield-produced water with a complex and highly variable water composition. This review article discusses the mechanisms and current state of heterogeneous photocatalytic systems for oilfield-produced water treatment, highlighting impediments to knowledge transfer, including the feasibility of practical applications and the identification of essential research requirements. Additionally, the effects of significant variables such as catalyst quantity, pH, organic compound concentration, light intensity, and wavelength were discussed in detail. Some solutions are proposed for scientists and engineers interested in advancing the development of industrial-scale photocatalytic water treatment technologies.

Produced Water Treatment with Conventional Adsorbents and MOF as an Alternative: A Review

A large volume of produced water (PW) has been produced as a result of extensive industrialization and rising energy demands. PW comprises organic and inorganic pollutants, such as oil, heavy metals, aliphatic hydrocarbons, and radioactive materials. The increase in PW volume globally may result in irreversible environmental damage due to the pollutants’ complex nature. Several conventional treatment methods, including physical, chemical, and biological methods, are available for produced water treatment that can reduce the environmental damages. Studies have shown that adsorption is a useful technique for PW treatment and may be more effective than conventional techniques. However, the application of adsorption when treating PW is not well recorded. In the current review, the removal efficiencies of adsorbents in PW treatment are critically analyzed. An overview is provided on the merits and demerits of the adsorption techniques, focusing on overall water composition, regulatory discharge limits, and the hazardous effects of the pollutants. Moreover, this review highlights a potential alternative to conventional technologies, namely, porous adsorbent materials known as metal–organic frameworks (MOFs), demonstrating their significance and efficiency in removing contaminants. This study suggests ways to overcome the existing limitations of conventional adsorbents, which include low surface area and issues with reuse and regeneration. Moreover, it is concluded that there is a need to develop highly porous, efficient, eco-friendly, cost-effective, mechanically stable, and sustainable MOF hybrids for produced water treatment.

Cost-Efficient De-Bottlenecking of Produced Water Treatment Systems through the Application of a Single Technology, Eliminating the Need for Hydrocyclones and Degassing Drums

Traditionally, produced water from production separators is handled by multiple steps and different technologies in order to meet the required quality for either discharge or reinjection of the water. The development of the latest Compact Flotation Unit (CFU) technology has unlocked the potential for savings on cost, complexity, footprint and weight for the produced water treatment system. The developed CFU technology has proven applicable through field testing as a single treatment technology for reducing Oil-in-Water (OiW) content directly from tie-in at separator and still meet stringent requirements for outlet OiW quality. Field tests were conducted with inlet OiW concentration ranging from 200-2000 ppm, achieving results in the range 2.5 to 21 ppm only with a two-stage latest generation CFU. Compared to a traditional produced water system setup consisting of de-oiling hydrocyclones and a horizontal degassing vessel, the savings in footprint and operational weight is estimated to 54 % and 53 % respectively utilizing a two-stage CFU for a system with a design capacity of 76.000 BWPD. Furthermore, the development of the latest generation CFU technology has enabled the retrofit concept, incorporating the developed CFU internals into existing gravity separation based produced water vessels, converting them to more efficient flotation vessels with increased capacity. For brownfield and debottlenecking applications, operators are challenged by increasing water cut from maturing wells, and as a result exceeding the facilities design capacity for produced water treatment. This challenge is often further reinforced by increasingly stricter environmental legislation for OiW content for discharge or re-injection. The retrofit concept will offer a highly cost-, footprint- and weight-efficient solutions to these challenges utilizing existing vessels. Benefits of the retrofit concept: Bring proven and unique performance of the technology to other produced water separation vessels helping the operators improve the separation efficiency and increase throughput while meeting discharge requirementsShort execution time compared to installation of new process equipmentLow cost compared to installation of new process equipmentUtilization of existing equipment saves valuable footprint.

Smart Upgrades to Maximize the Use of Existing Produced Water Treatment Facilities for CEOR

The maximum use of existing surface produced water treatment (PWT) facilities is a prerequisite for an economic chemical enhanced oil recovery (cEOR) in mature fields, as the erection of additional dedicated polymer treatment facilities can seriously harm the project's business case. These existing facilities often exhibit a reliable design, but do not necessarily fulfill the requirements of treating back-produced polymer. An optimization of installed facilities based on prior assessment of limitations is a way to upgrade facilities with regard to future EOR operations. Since its start-up in 2015, the main PWT plant comprised three separation stages: corrugated plate interceptors (CPIs), dissolved gas flotations (DGFs) and nutshell filters (NSFs). The plant processes up to 1,200 m3/h of conventional produced water at the Matzen field in Austria. Additionally, in 2009 a polymer injection pilot was initiated, with continuous polymer injection started in 2012, and now produces a segregated water stream containing back-produced polymer. Prior field tests with a pilot scale water treatment plant indicated operational issues with the existing set-up of facilities and the flotation chemicals used, with increasing polymer concentrations. At the end of 2018, severe injectivity issues were observed at injectors which were supplied with commingled conventional and polymer containing produced water. These were caused by a chemical interaction between the partially hydrolyzed polyacrylamide (HPAM) and alumina-based water clarifiers, which were applied in the dissolved gas flotation, finally leading to a loss of production. Therefore, a strict segregation of polymer and conventional streams at the common well network has been developed and established, where the separated streams could be injected into different parts of the injection system without any issues. This experience pointed out the future risks and hurdles of an economic cEOR full field roll-out where up to 200 ppm back-produced polymer at all surface treatment facilities is expected. Several studies were performed to identify alternative technologies able to treat polymer containing water. A business case driven option was to initiate an optimization program to develop smart upgrades and ensure maximum use of the existing PWT facilities. The main task was to substitute or stop the current poly-aluminum chloride-based coagulant in the DGF with a dosage of 40 to 60 ppm due to its unfavorable interactions with the back-produced HPAM. A technology assessment, comprehensive measures and economic retrofits of the installed gas dissolving units, the circulation cycle and bubble injection points resulted in a 200% higher flotation bubble bed density. Thanks to these improvements, the dosage of water clarifiers could be stopped, accomplishing similar or even better PWT performance values. In addition to the operational savings achieved, the existing treatment plant can now be used to treat cEOR fluids, as first tests with up to 59 ppm of back-produced polymer proved. Considering this new opportunity, a customized and economic modular cEOR debottlenecking concept was developed.

Produced Water Treatment Planning Using Corrugated Plate Interceptor and Ultra Filtration for Water Recycling

Produced water generated by the oil and gas industry, when treated properly, will produce water that is ready to be reused, such as for watering plants. This planning is done by treating the produced water with Corrugated Plate Interceptor (CPI) and Ultra Filtration units. This research aims to analyze the design details needed in the recycling of produced water with CPI and Ultra Filtration units. After determining the design criteria used, the dimensions for each unit are obtained. Data was collected using secondary data directly from the study site and quantitative method was used for data analysis. The land area for one CPI unit requires 55 m2 with a volume of 110 m3. The Reynolds number and Froude number for CPI units meet the design criteria with 419.8 and 0.24, respectively. The ultra-filtration unit was selected with a Flux specification of 0.15 m3/m2.hour with an operational duration of 24 hours. The results of processing with the CPI unit can at least produce oil and fat effluent of 0.038 mg/L, with the threshold for water quality is 1 mg/L. Produced water treatment planning with CPI configuration and UF membrane with storage tank requires a total land area of 63.97 m2..