Philippe Glenat

Kinetic Hydrate Inhibitors - Sensitivity towards Pressure and Corrosion Inhibitors

Replacement of the traditional thermodynamic hydrate inhibitors (methanol and glycols) in wet gas applications is more and more highly desirable for cost savings and for Health, Safety & Environment (HSE) considerations. This seems achievable by using alternative Kinetic Hydrate Inhibitors (KHI). KHIs are able to delay hydrate formation for the time needed to transport the effluents in hydrate region conditions.

QUALIFICATION OF LOW DOSE HYDRATE INHIBITORS (LDHIS): FIELD CASES STUDIES DEMONSTRATE THE GOOD REPRODUCIBILITY OF THE RESULTS OBTAINED FROM FLOW LOOPS

Replacement of the traditional thermodynamic hydrate inhibitors (methanol and glycols) in multiphase applications is highly desirable for Health, Safety & Environment (HSE) considerations and for investment costs savings. Low Dose Hydrate Inhibitors (LDHI) are good candidates to achieve this objective and their interest is growing in the E&P industry. There are two types of LDHI: the Kinetic Hydrate Inhibitors (KHI) and the Anti-Agglomerants (AA) also called dispersant additives. The main challenge with LDHIs is that they require the unprocessed effluents to be produced inside the hydrate stability zone. It is then of the utmost importance to select, qualify and implement properly LDHIs, so that their field deployment is performed with success. But due to the very stochastic nature of the nucleation step, the hydrate crystallisation process leads to very large discrepancies between performances results carried out at lab or pilot scales. In order to overcome this difficulty, we have developed an in-house special protocol which is implemented prior to each qualification tests series. This in-house 15 years old protocol consists in conducting each tests series with a fluids system having previously formed hydrates in a first step but followed by a dissociation step at moderate temperature for a few hours. This paper presents results selected from several field cases studies and obtained from our 80 bara and 165 bara flow loops. They show the very good reproducibility obtained with and without LDHIs. In the case of KHI, where the stochastic nature of the nucleation step is very critical, the results show that the deviation on the “hold time” for a given subcooling is less than 15%.

Successful field application of an inhibitor concentration detection system in optimising the kinetic hydrate inhibitor (KHI) injection rates and reducing the risks associated with hydrate blockage

Currently, hydrate inhibitors are injected at the pipelines upstream based on the calculated/measured hydrate phase boundary, water cut, worst pressure and temperature conditions, and the amount of inhibitor lost to non-aqueous phases. In general, no means of controlling and monitoring are available along the pipeline and/or downstream to assess the degree of inhibition. Often high safety margins are considered to accommodate for the uncertainties in the above parameters and to ensure gas hydrate risks are eliminated. However, despite these efforts hydrates do still form and this can result in considerable economical and safety concerns.

Heavy Oil Dilution

Heavy Oil Dilution — Heavy crude oils cannot be transported by pipeline without a prior reduction of their viscosity. This is commonly obtained by blending the oil with light hydrocarbons. In that case, the resulting viscosity of the mixture depends only on the dilution rate, on the respective viscosities and densities of the oil, and of the diluent. The addition of a polar solvent to a solution of asphaltenes in toluene acts on the colloidal structure of the asphaltenes. The relative viscosity of the solution decreases. Small-angle X-ray scattering (SAXS) measurements show that the radius of gyration of the aggregates of asphaltenes decreases too. In the same way, by mixing hydrocarbons and solvents owning polar functional groups in their molecule, it is shown that the efficiency of the dilution of heavy crude oils is enhanced. Hansen’s theory can be used to screen the solvent efficiency. At constant dilution rate, the higher the polarity parameter or the hydrogen bonding parameter of the solvent, the greater the relative viscosity reduction of the diluted crude oil. Nevertheless, solvent owning high hydrogen bonding are generally more viscous than hydrocarbons. The influence of their interactions with the asphaltenes is hidden when the results are expressed in absolute viscosity. Only polar solvents giving few hydrogen bonding give a significant reduction of the viscosity of the diluted crude oil. Pipeline Transportation of Heavy Oils Écoulement des bruts lourds dans les conduits D o s s i e r Oil & Gas Science and Technology – Rev. IFP, Vol. 59 (2004), No. 5

Pre-electrocoalescer Unit Adapted to the Extra-heavy Oil Characteristics

For Mobile Extra Heavy Oils (Cold production) and for Bitumen Extra Heavy Oils (Thermal production), dehydration process is based on solvent mixture with additives injection in order to break the Water in Oil emulsions. Dehydration requires injection of large amount of additives, relatively high operating temperature, solvent addition and long retention times inside the vessels. This process could be improved by electrocoalescence in order to reduce the amount of additive and possibly reduce the vessels retention times to finally reach the oil export specification. However, current commercial electrocoalescence processes have a low efficiency for Extra Heavy Oils because of the presence of polar heavy components limiting the electrocalescence effect and consequently limiting the efficiency of electrostatic coalescer. The objective is to determine the most efficient electrocoalescence parameters considering the characteristics of two types of heavy crude oils issued from Cold and Thermal productions: the aim is to optimize the development of a pre-electrocoalescer unit adapted to the extra-heavy oil characteristics. This paper presents experimental results for electrocoalescence additive selection and for the optimization of electrical parameters. The crude oils behaviour was analyzed considering their tendency to form an emulsion under controlled hydrodynamic conditions in relation with the oil/water interface dynamics. For the electrostatic dehydration, the optimization of the emulsion breaker concentration was performed using the Electrical Stability Tester API device. The minimum concentration that triggers electrical short-circuiting in relation with droplet coalescence was selected. The electrical parameters of the preelectrocoalescer device were determined in presence of the selected additive concentration. For the two types of crude oils, high voltage and high frequency up to 1 kHz are required in combination with the addition of solvent and additive in order to destabilize the water in oil emulsions. Correlation between dehydration efficiency and residence time under electrical stress is established.

Development of a Methodology for the Optimization of Dehydration of Extra-Heavy Oil Emulsions

SummaryWith the increasing development of heavy- and extraheavy-oil (EHO) fields, separation operations are becoming increasingly challenging compared to separation for conventional oil fields. For in-situ bitumen, EHOs produced by thermal-process dehydration require solvent addition, injection of a large amount of demulsifier additives, relatively high operating temperature, and long retention times inside the separators. So, in order to respect specifications on crude oil and water quality at lower cost, an optimization of the different parameters involved in the whole process of separation becomes necessary.In the case of EHOs, the presence of polar heavy components, such as asphaltenes, structured as a rigid film at the water/oil inter-face, limits the coalescence phenomena and, consequently, limits the efficiency of separation by gravity or by using conventional electrocoalescence.The paper presents a methodology that permits the optimization of water and oil separation in the case of an in-situ EHO (produced by thermal process). The crude oil was first characterized in terms of rheological behavior and interfacial properties. The dilatational viscoelastic properties of the interface were determined from measurements performed with an oscillating oil-drop tensiometer. Properties of emulsification were also investigated by using a specific device called a dispersion rig that allows the reconstitution of crude-oil emulsions under controlled hydrodynamic conditions. Then, a laboratory procedure based on electrical stability tests (ESTs) was applied to optimize the concentration of demulsifier required for effective water separation. Finally, the optimal electrical parameters were determined in an electrocoalescer device in the presence of the selected concentra-tion of additive. The efficiency of coalescence was measured by following the growth of dispersed water droplets inside the emul-sion using differential scanning calorimetry (DSC).This methodology may be used advantageously as a useful base for further scaleup studies concerning field separation facilities.IntroductionIn-situ EHOs produced by cold or thermal methods (e.g., steam-assisted gravity drainage) tend to form tight and stable emulsions containing oil, water, diluents, and solids. These emulsions have to be treated either by using conventional gravity-based vessels operating at high temperatures with long retention times and huge chemical injection or by using more-advanced technologies, such as electrostatic coalescers (Sams and Zaouk 2000; Noik et al. 2005, 2006; Eow and Ghadiri 2002).For thermal in-situ EHOs, such as the ones in Athabasca, elec-trocoalescence is scarcely used. This paper will present the specific case of one of these EHOs for which a rigorous methodology was applied in the laboratory to optimize water and oil separation by electrocoalescence. First, some chemical and physicochemical properties, such as rheological behavior and interfacial and emulsification properties, were investigated. Then, a laboratory procedure based on ESTs was applied to select an efficient demulsifier and to determine the optimal concentration required for an effective crude dehydration. Finally, emulsions from the extraheavy crude oils were submitted to electrocoalescence experiments at high frequency on a tubular electrocoalescer device developed in the French Institute of Petro-leum (IFP). The efficiency of coalescence determined by DSC allowed for the evaluation of the influence of parameters such as additive concentration, residence time under electrical field, and temperature. Materials and Methods