In the oil and gas industry, many different approaches have attempted to provide accurate predictions of the hydrodynamics and flow-related characteristics of fluids. However, factors such as modeling the concentration of a dispersed phase, the determination of drag and lift forces and relative motion between phases, and the need to consider particles with ranges of shape, size and density means that the only viable option in many situations is the use of computational fluid dynamics (CFD) to develop accurate solutions for challenging multiphase flow problems.
Topsides separators are designed to handle a relatively constant flow of liquid and gas, but may also have an allowance for slugs. Under certain operating conditions (low flow rate, over-sized flowline ID and unfavorable flowline profile), gas and liquid are not evenly distributed throughout the flowline, but consist of large plugs of liquid followed by large gas pockets. This is called slug flow.
As mentioned in Part 1, pigs are devices that travel through the pipeline and can be used for cleaning or maintenance purposes (utility pigs) as well as for gathering information about the condition, features and integrity of a pipeline (intelligent pigs).
Intelligent pigs are designed to identify different features or abnormalities as they travel through the pipe. Figure 1 briefly lists the functionalities for which intelligent pigs are commonly used. API 1160 and NACE RP0102 provide guidelines for selecting the appropriate tool for a given purpose. In this paper, the most commonly used In-Line Inspection (ILI) techniques, methodology and limitations applicable to detecting metal loss and wall thickness measurements are presented.
Build-up of deposits can create conditions for accelerated localized corrosion, which may be caused by under-deposit corrosion, localized acidic conditions and/or bacterial attack (microbiologically induced corrosion - MIC). This may result in sections of the pipeline needing repair or replacement before the end of their anticipated design life. Deposits will also impact throughput due to the reduction in the effective pipe diameter, which may require up to 140% increase in pressure in the line to maintain flow (Titratsoo 1).
This paper is the first part of a two part series and presents an overview of pig selection criteria for cleaning and maintenance of the pipelines, and covers high level guidance on establishing a progressive pigging strategy.
Asphaltenes are large, complex organic components present in the oil phase, along with resins, aromatic hydrocarbons, and alkanes (saturated hydrocarbons). Resins play an important role in stabilizing asphaltenes in crude oil. When the resins get destabilized, (under unfavorable pressure-temperature conditions) asphaltenes can agglomerate and deposit.
Hydrates and hydrate plugs can restrict flow, damage equipment, and potentially jeopardize the safety of personnel. Hydrates are formed as a result of the bond between gas and water molecules that occur at high-pressure, low-temperature environments. In deepwater, hydrates can form at temperatures higher than the ambient seabed temperature; hence, prevention and remediation of hydrates is a serious concern for deepwater operators.
Careful attention to scale inhibition during the first wave of water injection can reduce your headaches for the long term. Waterflood is a major secondary recovery option for maximizing field production and ultimate oil recovery. Scaling however, is a problematic issue, hindering secondary recovery by forming blockages that can plug vital waterflood components.
Scale has a large tendency to form immediately around the water injector completions due to the mixing of injected brine and formation brine. This is especially true during initial water injection and startup, before the formation water is fully swept away from the completion.
Scale that forms at the injector causes more concern than reservoir scale formation, because at the injector large volumes of processed seawater are being forced through a relatively small, fixed space. Hence, the presence of deposited scales at the injector is more detrimental to the system than scale dropout in the larger reservoir.