This multiauthor review article aims to bring readers up to date with some of the current trends in the field of process analytical technology (PAT) by summarizing each aspect of the subject (sensor development, PAT based process monitoring and control methods) and presenting applications both in industrial laboratories and in manufacture e.g. at GSK, AstraZeneca and Roche. Furthermore, the paper discusses the PAT paradigm from the regulatory science perspective. Given the multidisciplinary nature of PAT, such an endeavour would be almost impossible for a single author, so the concept of a multiauthor review was born. Each section of the multiauthor review has been written by a single expert or group of experts with the aim to report on its own research results. This paper also serves as a comprehensive source of information on PAT topics for the novice reader.

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Summary Paraffin deposition under single-phase flow conditions was investigated to determine its dependence on shear stripping, deposit aging, flow regime, temperature gradient, and fluid properties. In this study, a new model for the prediction of single-phase wax deposition has been developed. Most of the models previously used assume that equilibrium exists at the deposit-fluid interface. A kinetic resistance of the fluid is considered in the new model. Therefore, the interfacial-wax concentration might be different from the equilibrium-wax concentration. The model also includes continuous diffusion of wax into the deposit. We believe that this enrichment of the deposit is responsible for the increasing hardness of the deposit with time - a process known as "aging." The effect of shear stripping may also be incorporated in the prediction. The model predictions are compared with predictions from previous models, as well as with experimental data gathered at the Tulsa U. Paraffin Deposition Projects, with two different oils: a black oil and a condensate. Even though some tuning is required for each type of oil, the new model is based on physical phenomena, reducing the empiricism of previous models. Introduction In oil production and transportation systems, when the fluid temperature drops below the wax-appearance temperature, the long-chain normal paraffins of the formula CnH2n+2 where n>20 will solidify and adhere to the pipe walls, if a radial heat flux to the surroundings exists. This phenomenon, known as "paraffin deposition," can cause a reduction in the effective flow area. Paraffin deposition can result in significant operational and remedial costs, reduced or deferred production, well shut-ins, and pipeline replacements and/or abandonment. It is imperative to properly identify the conditions for paraffin precipitation and to predict paraffin deposition rates for the design and optimization of oil- and gas-production systems, as well as to implement proper strategies for prevention and remediation. Understanding the paraffin deposition process under single-phase flow conditions is crucial to properly model the phenomena under both the single-phase and multiphase flow conditions encountered in oil-production systems. Model Enhancement One of the main limitations in the current Tulsa U. (TU) single-phase paraffin deposition model1 is the assumption of constant oil fraction in the deposit that the user is required to specify as an input parameter. It is also assumed that all the mass flux from the bulk fluid contributes to deposit growth, and no diffusion into the deposit is considered. The current model does not consider the aging effect on the deposition process. Singh et al.2 proposed a model that considers the diffusion of wax into the existing deposit. The boundary condition used at the deposit-fluid interface was that the diffusion flux at the interface is equal to the slope of the wax solubility curve in equilibrium with the deposit temperature gradient. In this thin film model, the wax fraction in the deposit changes with time, but it is uniform across the deposit. Also, Singh et al. did not consider any shear-stripping effects, as all of their tests were conducted under laminar flow conditions. The new model proposed in this paper is analogous to the Singh et al. model in the sense that it also considers that part of the bulk flux will contribute to new deposit growth, and the rest will be diffused into the existing deposit. The model considers a kinetic resistance for the diffusion into the deposit; therefore, the interfacial concentration might be different from the equilibrium concentration at the interface temperature. The kinetic resistance would be different for different oils. Also, the proposed model assumes that the deposit layer is immobile.

Paraffin deposition is a very complex phenomenon. Whenever paraffinic oil comes in contact with a cold pipe wall that is below the wax appearance temperature (WAT) of the oil, solid paraffin crystals can precipitate and deposit on the pipe surface. This may significantly reduce or even block the area open to flow.Most oil fields produce water along with the oil, and the deposition process is not well understood for oil/water flow conditions. Very few studies have been conducted to investigate the effect of water on the deposition process.The objective of this study is to investigate paraffin deposition under different oil/water conditions. The tests were conducted using a cold-finger device and a crude oil from the Gulf of Mexico. Emulsions were created with both fresh water and brine. A simple oil/water wax-deposition model was developed by modifying the current University of Tulsa single-phase deposition model for solubility and physical properties of the mixture as a function of water content.

Slurry transport has become a subject of interest in several industries, including oil and gas. The importance of slurry/solid transport in the oil and gas industry is evident in areas of cuttings transport, sand transport and, lately, hydrates. There is therefore a great need to develop instrumentation capable of characterizing fluids with high solid content. Presence of solids in fluids makes the rheological characterization of these systems difficult. This is because available rheometers are designed with a narrow gap and cannot prevent solids from settling. The main aim of this paper is to present a step-by-step procedure of converting torque and shaft speed into viscosity information by applying the Couette analogy, equivalent diameter and inverse line concepts. The use of traditional impeller geometries such as cone and plate may be challenging due to their narrow gap and inability to prevent settling. Therefore, the use of nonconventional impeller geometry is imperative when dealing with settling slurries and suspensions. The most challenging task using complex geometry impeller is data interpretation especially when dealing with complex rheology fluids. In this work, an autoclave is transformed into a mixer-type viscometer by modifying its mixing, cooling and data acquisition systems. Mathematical models relating the measured torque to shear stress and the measured shaft speed to shear rate were developed and expressed in terms of the equivalent diameter. The shear rate and shear stress constants were expressed in terms of equivalent diameter and measureable parameters such as impeller speed and torque. The mixer-type viscometer was calibrated using four Newtonian and four Power-Law fluids to determine the rheological constants (equivalent diameter, shear rate and shear stress constants). The concept of inverse line was used to identify the laminar flow regime. The calibrated instrument was used to characterize two Power-Law fluids. This procedure can be extended to any rheological model. Methods developed in this work can be used to characterize fluids with high solid content. This is particularly important when dealing with complex rheology slurries such as those encountered in food processing, oil and gas and pharmaceuticals.Keywords Rheology Á Settling and non-settling slurries Á Hydrate slurry List of symbolsImpeller diameter (m) k