They assist oil/water/gas separation, aid in fluid transport, protect treating equipment, and improve the quality of the gas, oil, and water. A wide range of chemicals is available for water treating. A chemical-injection package enables various types of chemicals to be dosed into the water stream to optimize the treatment process. Storage-tank capacity is designed to allow the plant to run for several days between refills. General dosing rates and injection points for the main chemical classes are listed in Table 1. These rates provide guidelines for sizing injection pumps and chemical-storage tanks. Water-clarification chemicals aid in coagulating and flocculating the oil and solid particles into larger ones to enhance their separation from water.
Produced water typically enters the water-treatment system from a two- or three-phase separator, free-water knockout, gun barrel, heater treater, or other primary-separation-unit process. This water contains small concentrations (100 to 2000 mg/L) of dispersed hydrocarbons in the form of oil droplets. Because the water flows from this equipment through dump valves, control valves, chokes, or pumps, the oil-particle diameters will be very small ( 100 μm). Treatment equipment to remove dispersed oil from water relies on one or more of the following principles: gravity separation (often with the addition of coalescing devices), gas flotation, cyclonic separation, filtration, and centrifuge separation. In applying these concepts, one must keep in mind the dispersion of large oil droplets to smaller ones and the coalescence of small droplets into larger ones, which takes place if energy is added to the system. The amount of energy added per unit time and the way in which it is added will determine whether dispersion or coalescence will take place. Stokes' law, shown in Eq. 4.1, is valid for the buoyant rise velocity of an oil droplet in a water-continuous phase. Several immediate conclusions can be drawn from this equation. The third conclusion requires further elaboration. Heat is the primary mechanism in oil-treating equipment to remove small water droplets from oil. The addition of heat significantly reduces oil viscosity, which prompts more rapid settling, and heat destabilizes water-in-oil emulsions. Heat is not commonly used in water treating because the percentage change in viscosity per degree of temperature change is much less in water than in oil. Water-in-oil emulsions tend to have a higher percentage of the dispersed phase than the oil-in-water emulsions; the dispersed phase tends to have larger-diameter droplets stabilized by heat-sensitive emulsifiers, and it takes twice as much heat input to raise a barrel of water as it takes to raise a barrel of oil to the same temperature. Small oil droplets contained in the water-continuous phase are subject to the competing forces of dispersion and coalescence.
In many operations worldwide, surface waters are injected into producing formations to enhance oil recovery. The types of surface waters used range from seawater (salt water) to lake water (brackish) to river water (fresh water). Surface water must be treated to remove undesirable components before injection. Treatment of surface water for injection requires a specially designed system made up of various components to remove or control any contaminants in the water. The system is engineered to perform the required treatment in the most cost-effective and environmentally sensitive manner. A typical system is shown in Figure 1. The type, concentration, and particle-size distribution of suspended solids in water will vary depending on the source of the surface water.
Understanding the causes of this type of formation damage is important so that efforts to prevent it can be undertaken. This page discusses the types of formation damage that affect injection wells. In such projects, the cost of piping and pumping the water is determined primarily by reservoir depth and the source of the water. However, water treatment costs can vary substantially, depending on the water quality required. In most cases, the well injectivity is a crucial factor in determining the cost of water injection.
Enhanced oil recovery processes, particularly offshore, create challenges for produced water treatment. Higher oil prices has created increased interest in chemical enhanced oil recovery (CEOR) using polymers, surfactants, and alkalis. This technology poses some special challenges, especially around water treatment.
Polymer flooding in sensitive areas can require the transport of polymer fluids over long distances. Conventional wisdom limits transport distance or degradation occurs. This paper argues that critical velocity, not distance, is the controlling factor. Polymer flooding has been used to enhance the production of oil from mature fields in Oman. This article discusses the trial of several approaches to improve the treatment of water produced from these fields.
Produced water from chemical floods can cause problems for separation and water treatment equipment due to the polymers and surfactants used. Challenges are greater offshore where space limitations can affect treatment options. A variety of low-cost technologies can result in an increase in production in mature oil and gas fields, although the increase is usually temporary and not always economical.
In the complete paper, three stages of review have been combined to find out the applicability of the most-feasible improved-oil-recovery (IOR) methods in North American unconventional reservoirs. The US Energy Information Agency reports that the country is seeing petroleum exports rise across the board and notes serveral drivers for this trend. This paper describes functional water-treatment steps that target the most common removal of suspended solids and oil or condensate from Produced-water (PW) and flowback-water (FW) for recycling or disposal operations.
Aker Solutions and FSubsea have agreed to a joint venture, named FASTSubsea, to help operators increase oil recovery. High-concentration polymer flooding can improve oil-displacement efficiency but separation of oil/water mixture becomes more difficult because of emulsification. In this work, a case history of dehydration technology for HCPF production and lab investigation of emulsion behaviors are reviewed. The authors discuss the results of a pilot project to capture post-combustion CO2 for purposes of EOR. Produced water from chemical floods can cause problems for separation and water treatment equipment due to the polymers and surfactants used.
Zagitov, Robert (Cairn Oil & Gas, Vedanta Ltd) | Venkat, Panneer Selvam (Cairn Oil & Gas, Vedanta Ltd) | Kothandan, Ravindranthan (Cairn Oil & Gas, Vedanta Ltd) | Senthur, Sundar (Cairn Oil & Gas, Vedanta Ltd) | Ramanathan, Sabarinathan (Cairn Oil & Gas, Vedanta Ltd)
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 Performance of production chemicals in the presence of polymer Solids loading in production system Emulsion and produced water treatment Suitability of produced water treatment facilities Revised scaling and fouling control with back produced polymer with rich divalent ions present in produced water Strategizing chemical management system to suit polymer flood and polymerized back produced water treatment regime
Selection of production chemicals to be compatible to polymer so that no or minimal degradation or loss of viscosity due to polarity of chemicals
Performance of production chemicals in the presence of polymer
Solids loading in production system Emulsion and produced water treatment
Suitability of produced water treatment facilities Revised scaling and fouling control with back produced polymer with rich divalent ions present in produced water
Strategizing chemical management system to suit polymer flood and polymerized back produced water treatment regime