Treatment

Enhanced Oil Recovery is important stage of life cycle of a field and often it is implemented with challenges. In the chemical EOR, challenges and surprises are expected in production chemistry and production facilities operations. Partially hydrolyzed polyacrylamide used widely for controlling mobility ratio so that Operator is able to recover maximum possible oil. With complex water chemistry and rich in positively charged divalent ions, flooded polymer having negative charge interacts with divalent ions of produced water. Back produced sheared polymer interacts with divalent ions to form semi hard to hard scales poses challenges of the reliability of production facilities.

Other important limitations to be noted in CEOR phase are using production chemicals to control scale, emulsion and microbial treatment under Hydrogen Sulphide and waxy crude environment. This paper discusses about the requirement of preparedness and how to overcome challenges of EOR operations and in handling the back produced polymer in following areas:

Selection of production chemicals to be compatible to polymer so that no or minimal degradation or loss of viscosity due to polarity of chemicals

Steam and flue gas stimulation technology has been applied for heavy oil exploitation in Bohai Oilfield for almost ten years. For the special fuel and water requirement of the current thermal generator, large amount of diesel and desalinated seawater are needed during the thermal injection process. Besides, treatment of the produced oily wastewater on the platform becomes more difficult as the oil output increases.

Aimed at solving the existing problems and taking the advantage of characteristics of the supercritical water, a new type of supercritical steam and flue gas generator for offshore oilfield is proposed and studied. The newly proposed generator is mainly consisted of two sections, which are the supercritical water gasification reactor and combustion reactor, respectively. The produced oily wastewater could be directly used for steam generation. A series of experiments are carried out for its feasibility research and structure optimization.

A prototype of the generator is made for indoor experiment. During the gasification process, wastewater and the organic material mixed inside is placed in the supercritical conditions in the gasification reactor whose temperature and pressure are about 600-700°C and 23MPa, respectively. And the reaction product would be mainly H₂, CO₂ and water. Gasification Experiments of both the diesel and oily wastewater are conducted. And the combustion experiment is also conducted and the gasified gas is reacted with O₂ under conditions of 25MPa and 500-550°C. Composition of the produced fluid in each experiments are analyzed. Besides, the structure of the generator is also designed and optimized for improving its working efficiency.

The proposed new-type supercritical steam and flue gas generator has the characteristics of high efficiency, waste water treatment and higher temperature and pressure delivery capacity. And there would be a promising perspective for its application on offshore platform.

Ordos basin is known for its tight sandstone formations and fracturing has been the most effective approach to improve production^[1,2]. With increasing stimulation activities, water consumption, and associated water cost, flowback fluid volume also increased dramatically. Successfully treat the flowback fluid and the reuse of the treated fluid in making new frac fluid are keys to improve stimulation economics and protect the environment. However, treatment and reuse of commonly used guar frac fluid system remains a significant challenge to operators and service companies.

To successfully treat and reuse flowback fluid in Ordos basin, two major obstacles have to be overcome: First, in the fracturing process, the local common practice is to add the entire designed amount of gel breaker at the end of propant pumping job, to avoid sand plugging and sanding out. This incorrect, but common practice results in incomplete breaking of gel of the frac fluid, which inevitably flows back leading to greatly increased difficulties in flowback fluid treatment. Secondly, organic boron crosslinking agent is widely used as crosslinking agent in the guar fluid system in this area. As boron compounds are extremely difficult to be removed during flowback fluid treatment, proven treatment methods alone cannot make the treated water reusable in making new frac fluids.

Technology and processes were developed to manage four key factors that affect the performance of guar frac fluid configured with treated flowback fluid: a) Metal ions, b) Bacteria, c) Breaking agent, d) Crosslinker. Mobile units developed in association with treatment processes and agents also help avoid secondary pollution from the transportation of fresh and flowback fluid. In 2017 and first quarter of 2018, more than 15,000 cubic meters of flowback fluid have been successfully treated and reused. One third of the treated water was guar frac fluid and was reused in making new frac fluid, reducing the need for fresh water significantly. Fracturing service company conducted tests on the treated water and found that the performance of the fluid configured with the treated water completely satisfy the requirements of the SY/T6376-2008 "General Technical Requirements for Fracture Fluid" and SY/T 5523-2016 "Oilfield Water Analysis Method" standard. Frac fluid configured with the treated water was successfully applied to the stimulation jobs of horizontal wells, resulting in double savings to the operators: purchase of fresh water and transportation of flowback fluid (to treatment centers) and fresh water, also avoided secondary environmental impacts such road safety hazard and fluid seepage.

With the treatment and reuse of flowback fluid, savings up to 8% of total frac costs per well were observed which could lead to 100+ million RMB within 2018 alone. Most importantly, the technology can effectively relieve environmental pressure and reduce the need of fresh water which is a scarce in this area.

Produced water is an inextricable part of the hydrocarbon recovery processes. Safe and environmentally benign disposal of produced water is a major concern for all the oil fields across the world in the present low cost and stringent environmental & statutory compliance era. Many technology available in the market to treat produced water oil contaminants but economical treatment of heavy metal content is still a great challenges for oil industries for safe disposal.

Therefore, New innovative technology i.e. Reed bed technology has been adopted in Heglig field of Sudan to treat the produced water and heavy metal economically through phytoremediation. After successful implementation in Heglig oil field, it is being implemented in other surrounding oil field also.

It is probably a world largest Phytoremediation/Bio-remediation system using Reed Bed technology operating successfully for last 15 years. It is environmental friendly, solar energy driven clean up techniques. This paper not only elucidate, how reed bed removes oil contaminants and heavy metals but also provide clear picture of how this project provide shelter for flora, fauna, other species that help to maintain ecological and environmental balance. Research has also demonstrated that reed-bed technology is feasible and resilient in treating oil produced water

Produced water treatment (PWT) continues to be a challenge. New technologies continue to be discovered to both treat produced water and do it in a way that creates an expectation to meet overboard discharge requirements. In addition, it is incumbent on engineers to reduce the overall footprint of the treatment system. The challenge is always to make the system more compact but also to ensure meeting water quality throughout the lifetime of the platform. Simple, vertical and compact are all words to describe the new technologies but longevity of treatment as the water cut increases is always the question. Are we choosing technologies with maximum oil and grease removal in mind or are we basing our equipment decisions with a bias on space requirements only? We hope to make a comparison of past present and future technology to find an answer.

In this study, a pilot plant with a capacity of 50 m3/d was used to conduct flotation, filtration, and adsorption trials for produced-water treatment at a crude-oil gathering facility. The number of offshore facilities employing waterflooding with desalination continues to grow. Currently, more than 50 sulfate removal units are in operation offshore with a total capacity of approximately 8 million BWPD.

Water treatment systems in the North Sea differ from those in the deepwater Gulf of Mexico (GOM). This paper provides a detailed understanding of these differences and provides insight into the design of water-treatment systems in general. In this study, a pilot plant with a capacity of 50 m3/d was used to conduct flotation, filtration, and adsorption trials for produced-water treatment at a crude-oil gathering facility. A recent webinar covered the varieties of current technology for flotation equipment and provided an in-depth look into flotation technology and the options surrounding offshore applications. The author reviews advances in produced water treatment, particularly offshore, since the 1960s.

Water treatment systems in the North Sea differ from those in the deepwater Gulf of Mexico (GOM). This paper provides a detailed understanding of these differences and provides insight into the design of water-treatment systems in general. A recent webinar focused on hydrocyclones and their application for offshore oil and water separation. The discussion includes fundamental science, practical considerations, implementation and field experience. The author reviews advances in produced water treatment, particularly offshore, since the 1960s.

While storage and logistics are critical elements of the viability of water reuse, if the water chemistry is not fit for gel fracturing formulations, it will not matter how much is stored in centrally located impoundments. This paper reports on performance of an advanced MVR system in north-central Texas. With inconsistent inlet water quality being the rule rather than the exception, sizing and operational considerations of the treatment system components must vary accordingly to make the most economic sense. The demands for the fresh water used in many hydraulic fracturing operations are placing pressure on water sources in some regions of the United States. Because of the high volumes of water needed for fracturing and competing demands availability of fresh water has decreased and costs have grown.

While storage and logistics are critical elements of the viability of water reuse, if the water chemistry is not fit for gel fracturing formulations, it will not matter how much is stored in centrally located impoundments. A recent webinar discussed current technologies to enable reuse of produced water in gas and oil shale developments.