Flow assurance is crucial in the oil industry since it guarantees the success and economic production of hydrocarbon fluid, especially in offshore and deep water oil fields. In fact, the ultimate goal of flow assurance is to maintain flow in the wellbore and pipelines as long as possible. One of the most common challenges in flow assurance is the buildup of solids, such as asphaltene and scale particles. These Solid particles can deposit in the wellbore, flowline, and riser and affect the wellbore performance by reducing the cross section of the pipeline, which eventually results in pipeline blockage. Hence, neglecting the importance of flow assurance problems and failure in thorough understanding of the fluid behavior in the production systems may result in plugged pipeline, production loss, flowline replacement, and early abandonments of the well. As a result, continuous evaluations are needed at the development stage and during the life of reservoirs to predict the potential, the extent, and the severity of the problem to plan for inhibition and remediation jobs. In fact, it is more preferable to prevent flow assurance problems through the designing and operating procedures rather than remediating the problems, which has higher risks of success and higher loss of revenue due to frequent well shut down. As a part of this research, we enhanced the capabilities of our in-house compositional wellbore simulator (UTWELL) to model various production and flow assurance scenarios. Initially, we developed and implemented a robust gas lift model into UTWELL to model artificial lift technique for reservoirs with low pressure. The developed model is able to model both steady state and transient flow along with blackoil and Equation-of-State compositional models. The improved version was successfully validated against a commercial simulator. Then, we applied our dynamic model to track the behavior of asphaltene during gas lift processes and evaluated the risk of asphaltene deposition. Several deposition mechanisms were incorporated to study the transportation, entrainment, and deposition of solid particles in the wellbore. The simulation results illustrated the effect of light gas injection on asphaltene deposition and well performance. Finally, a step by step algorithm is presented for coupling a geochemical package, IPhreeqc, with UTWELL. The developed model is able to model homogenous and heterogeneous, non-isothermal, non-isobaric aqueous phase reactions assuming local equilibrium or kinetic conditions. This tool was then utilized to model scale deposition in the wellbore for various scenarios. In addition, the results showed that integrating IPhreeqc has promise in terms of CPU time compared to the traditional approach of reading and writing the input and output files. / text

A rigorous three-phase asphaltene precipitation model was implemented into a compositional reservoir simulator to represent and estimate the reduction of porosity and permeability responsible for productivity impairment. Previous modeling techniques were computationally inefficient, showed thermodynamic inconsistencies, or required special laboratory experiments to characterize the fluid. The approach developed in this study uses a cubic equation of state to solve for vapor/liquid/liquid equilibrium (VLLE), where asphaltene is the denser liquid phase. Precipitation from the liquid mixture occurs as its solubility is reduced either by changes in pressure (natural depletion), or composition (i.e. mixing resulting from gas injection). The dynamic relationship between phase composition, pressure, and porosity/permeability is modeled with a finite differences reservoir simulator and solved using an implicit-pressure, explicit-saturations and explicit-compositions (IMPESC) direct sequential method. The robustness of this model is validated by the ability to reproduce experimental asphaltene precipitation data while predicting the expected phase behavior envelope and response to key thermodynamic variables (i.e. type of components and composition, pressure and, temperature). The three-phase VLLE flash provides superior thermodynamic predictions compared to existing commercial techniques. Computer performance analysis showed that the model has a comparable cost to existing asphaltene precipitation models, taking only 1.1 more time to calculate but requiring fewer tunable parameters. The VLLE flash was in average 4.47 times slower compared to a conventional two-phase vapor/liquid flash. This model has the speed of a flash calculation while maintaining thermodynamic consistency, enabling efficient optimization of reservoir development strategies to mitigate the detrimental effects of asphaltene precipitation on productivity.

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Thesis (M.Eng.). / Written for the Dept. of Chemical Engineering. Title from title page of PDF (viewed ). Includes bibliographical references.

Polymers of various types are added to crude oils and oil products to prevent wax deposition, break water-in-oil emulsions, reduce drag in pipelines and to stabilize asphaltenes. In mixtures where a polymer does not adsorb on colloids, two stable liquid phases can arise due to depletion flocculation. Asphaltenes in heavy oils and toluene mixtures form sterically stabilized colloidal particles. In this work, the addition of a non-adsorbing polymer (polystyrene) to C5 Maya asphaltene + toluene mixtures was investigated experimentally and theoretically. As concentrated asphaltene + toluene mixtures are opaque to visible light, phase volumes and compositions were detected using ultrasound. The sensors comprised two commercial 64 element phased-array acoustic probes. The operation of the view cell, and kinetic and equilibrium data processing procedures were validated using mixtures of methanol + alkanes. Acoustic speed and attenuation profiles were found to provide independent measures of phase separation. At equilibrium, acoustic speed profiles are uniform in each phase with a step change at the interface. Acoustic wave attenuation profiles exhibit a sharp peak/spike at liquid-liquid interfaces. Mixtures of asphaltenes + polystyrene + toluene are shown to exhibit liquid-liquid phase behavior over broad ranges of composition. This is the first report of liquid-liquid phase behavior for such mixtures. One phase is asphaltene rich and the other phase is polystyrene rich. Liquid-liquid critical points were also identified along the liquid-liquid/liquid phase boundary for mixtures with two mean molar masses of polystyrene. Compositions of co-existing phases were computed using phase volume variations along dilution lines, acoustic speed data and a mass balance model. A parameter was introduced to improve the agreement between calculated and experimental speeds of sound. The results of the model indicate that more than half of the asphaltenes, by volume, participate in the depletion flocculation process. Phase compositions were measured independently using UV-visible spectrophotometry. The nominal size of asphaltene colloidal particles participating in the phase separation mechanism was estimated by comparing calculated phase boundaries with the experimental phase diagram. The estimated size of asphaltene colloidal particles is in agreement with the expected size of asphaltenes in toluene mixtures obtained exogenously. / Chemical and Materials Engineering

This Thesis presents the results of phase behavior calculations and simulation of asphaltene precipitation, flocculation, and deposition in five Middle-Eastern wells from different fields, based on a reliable experimental data provided for this purpose. The asphaltene precipitation, flocculation, and deposition have been simulated throughout the primary (pressure depletion), secondary (Waterflooding) and tertiary recovery (CO₂ injection) stages. Asphaltene precipitation becomes a serious problem especially when it causes plugging of the formation, wellbore, or production facilities, which will significantly affect the productivity and final recovery of the area. To help preventing asphaltene precipitation a bottomhole pressure higher than the asphaltene onset pressure (AOP) has been applied. Also, water and CO₂ injection has provided enough support for pressure maintenance, which helps in preventing asphaltene. Several scenarios were tested to investigate and identify the cases with lowest asphaltene precipitation and higher recovery. It has been considered obligatory to have a representative numerical simulation model that can predict the phase behavior of asphaltene precipitation, flocculation, and deposition accurately. The first part of this thesis includes a comprehensive literature review of asphaltene precipitation flocculation, and deposition that include asphaltene structure, models and prevention techniques. The second part of the thesis includes a detailed study of modeling asphaltene precipitation phase behavior utilizing experimental and real field data obtained from five Middle-Eastern wells from different fields. Experimental data include measurements of asphaltene onset pressure (AOP), saturation pressure, and PVT data. Asphaltene precipitation was modeled by using WinProp (a phase behavior utility from CMG) which uses Nghiem solid model. Saturation pressures, PVT, and AOP data were used to match Peng-Robinson EOS and the precipitation model was matched by the experimental data of AOP. The third part of the thesis includes a one-dimensional simulation comparison study of asphaltene precipitation between three different compositional simulators; UTCOMP, ECLIPSE and CMG/GEM. The last part of the thesis includes a full field scale study based on a heterogeneous three-dimensional cartesian single-well model. The objective of this study was to assess the effect of asphaltene precipitation, flocculation, and deposition in the well productivity and the economic impacts related to it. Different production practices were applied to define the most appropriate and efficient production strategy. This study includes a discussion and comparison of production rates with and without asphaltene precipitation, flocculation, and deposition and a comparison of asphaltene precipitation, flocculation, and deposition at different times using different bottomhole and production rate constraints. Several cases (i.e., WAG cycles, completion, target layers of injection, etc.) will be tested to come up with the optimum completion and operating strategy in the presences asphaltene. Despite the work devoted to understanding this subject, asphaltene still represents a challenging and unresolved problem. This thesis will help bridge the gap of this limited understanding in the field of asphaltene. / text

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