A Novel Technique for Determination of the Onset of Alkane Induced Asphaltene Precipitation Using Accurate Density Measurements

Onset of asphaltene precipitation is the key parameter in dealing with asphaltene problems because it is the starting point of the asphaltene separation from the solution. In this study, a new technique is provided based on the experimental observations for the determination of the onset of asphaltene precipitation using accurate density measurements of the crude oils upon titration with precipitating agents like n-alkanes. Moreover, density measurements have been conducted for three different crude oils diluted with different ratios of precipitating agents, i.e. n-pentane, n-hexane, and n-heptane. The experimental results confirmed that, as it was expected, the density showed a decreasing trend as the dilution ratio increased, except at one point, at which the density increased with raising dilution ratio; this corresponded to the onset of asphaltene precipitation. For all the crude oils used, a sample diluted with a non-precipitating solvent (toluene) was also used as a reference system, its densities were measured upon titration with toluene, and the results were used for comparison with the other systems diluted with precipitating solvents. The measured onsets of asphaltene precipitation using this technique were confirmed with the onsets obtained by using interfacial tension approach

A computational intelligence scheme for prediction of interfacial tension between pure hydrocarbons and water

Interfacial tension plays a major role in many disciplines of science and engineering. Complex nature of this property has restricted most of the previous theoretical studies on thermophysical properties to bulk properties measured far from the interface. Considering the drawbacks and deficiencies of preexisting models, there is yet a huge interest in accurate determination of this property using a rather simple and more comprehensive modeling approach. In recent years, inductive machine learning algorithms have widely been applied in solving a variety of engineering problems. This study introduces least-square support vector machines (LS-SVM) approach as a viable and powerful tool for predicting the interfacial tension between pure hydrocarbon and water. Comparing the model to experimental data, an excellent agreement was observed yielding the overall squared correlation coefficient (R2) of 0.993. Proposed model was also found to outperform when compared to some previously presented multiple regression models. An outlier detection method was also introduced to determine the model applicability domain and diagnose the outliers in the gathered dataset. Results of this study indicate that the model can be applied in systems over temperature ranges of 454.40–890 °R and pressure ranges of 0.1–300 MPa

Toward genetic programming (GP) approach for estimation of hydrocarbon/water interfacial tension

The interfacial tension (IFT) of hydrocarbon/water system is one of the most important parameters in various fields of chemical, petroleum and process industries. Laboratory measurement of interfacial tension is laborious, time demanding and involves costly experimental setup. Current study presents genetic programming (GP) as a powerful tool in order to develop a novel correlation for estimation of IFT in hydrocarbon/water systems under wide ranges of experimental conditions. To achieve this mission, a comprehensive databank comprising 1075 experimentally measured data points were acquired from the literature reports. Four influencing factors of hydrocarbon critical temperature, experiment temperature, pressure and hydrocarbon/water density difference were considered as independent correlating variables to design and develop the correlation. Comprehensive error analysis demonstrates the superiority of the proposed correlation with R2 = 0.91 and AARD = 4.38% in comparison with literature data. The predictability of the genetic model was further compared with a recently published model and other well-known empirical correlations reported in literature. The result suggests that the proposed tool is of great value for fast and precise estimation of hydrocarbon/water IFT

Efficient estimation of hydrolyzed polyacrylamide (HPAM) solution viscosity for enhanced oil recovery process by polymer flooding

International audiencePolymers applications have been progressively increased in sciences and engineering including chemistry, pharmacology science, and chemical and petroleum engineering due to their attractive properties. Amongst the all types of polymers, partially Hydrolyzed Polyacrylamide (HPAM) is one of the widely used polymers especially in chemistry, and chemical and petroleum engineering. Capability of solution viscosity increment of HPAM is the key parameter in its successful applications; thus, the viscosity of HPAM solution must be determined in any study. Experimental measurement of HPAM solution viscosity is time-consuming and can be expensive for elevated conditions of temperatures and pressures, which is not desirable for engineering computations. In this communication, Multilayer Perceptron neural network (MLP), Least Squares Support Vector Machine approach optimized with Coupled Simulated Annealing (CSA-LSSVM), Radial Basis Function neural network optimized with Genetic Algorithm (GA-RBF), Adaptive Neuro Fuzzy Inference System coupled with Conjugate Hybrid Particle Swarm Optimization (CHPSO-ANFIS) approach, and Committee Machine Intelligent System (CMIS) were used to model the viscosity of HPAM solutions. Then, the accuracy and reliability of the developed models in this study were investigated through graphical and statistical analyses, trend prediction capability, outlier detection, and sensitivity analysis. As a result, it has been found that the MLP and CMIS models give the most reliable results with determination coefficients (R2) more than 0.98 and Average Absolute Relative Deviations (AARD) less than 4.0%. Finally, the suggested models in this study can be applied for efficient estimation of aqueous solutions of HPAM polymer in simulation of polymer flooding into oil reservoirs

Equilibrium Modelling of Interactions in DETPMP-Carbonate System

Scale inhibitor (SI) squeeze treatments are widely used for the prevention of inorganic scale deposition in oil and gas production operations. This may be an expensive operation and its efficiency depends on the degree of SI retention in the formation. Carbonate formations are known to be highly reactive, where the SI retention is driven by both adsorption and precipitation of SI and SI-Ca/Mg complexes. To design and carry out this type of squeeze treatment, a comprehensive model capable of simulating SI retention in carbonate formations is required. In this study, a model has been developed to fully characterize the retention of DETPMP in a carbonate system. This model considers all the equilibrium reactions coupled with precipitation and adsorption processes to simulate the equilibrium of a DETPMP-Calcite-brine system containing free Ca2+ and Mg2+ cations. To equilibrate this system, the following coupled reactions were considered: (i) the full aqueous carbonate system, (ii) SI speciation by dissociation (SI is considered as a weak n-poly acid, HnA), (iii) SI impurities and their reactions, (iv)SI-Ca and SI-Mg complexation, (v)the associated adsorption and precipitation of the SI/Ca/Mg complexes. These reactions may be coupled together through the equilibrium equations, the mass balance of base species and the system charge balance. After some algebra, the system of equations is reduced and solved by Newton Raphson to find the concentration of key primary species from which the concentration of all other species is calculated and the equilibrium of the entire couple system is characterized. In the entire system, there may be up to ~100 species involved in the chemical equilibrium equation set. The adsorption process is characterized by an adsorption isotherm, Γ(C), which can be a reversible process. In the examples presented, the adsorption is considered to proceed in both directions of adsorption and desorption. Precipitation (denoted Π) is coupled with the adsorption (and the rest of the system) to satisfy the SI solubility by removing further SI from the solution, if required, through the complex SI species that may physically precipitate. Finally, the proposed model was validated against coupled adsorption-precipitation experiments. The results showed very good agreement between the model and experiments and confirmed the reliability and validity for various conditions and DETPMP concentrations

Experimental investigation of the effect of TiO

In petroleum industries, nanofluids have the potential to improve the characteristics of the fluids used in drilling wells or Enhanced Oil Recovery (EOR) processes. In this study, a water based mud containing polymer was considered as the base fluid. Different concentrations of TiO2 nanoparticle (0, 0.5 and 0.75 wt%) and different concentrations of KCl salt (0, 0.5, 1.5, and 3 wt%) were added to the base fluid and exposed to different temperatures (30, 50, 70 and 90 °C) with 19 different shear rates for investigating the effects of nanoparticle concentration, salt concentration, temperature and shear rate on viscosity of the base mud. Presence of TiO2 particles enhanced not only the rheological behavior but also electrical and thermal conductivity of fluid up to 25% and 43%, respectively. Furthermore, the stability of the fluid containing salt and nanoparticle was investigated in these temperatures owing to the fact that the temperature could cause degradation of the fluid. For the purpose of investigating this phenomenon, the after cooling experiment was conducted. In addition, the data gathered in this investigation were examined by using three famous rheological models (Power law, Herschel-Bulkley and Herschel-Bulkley-Papanastasiou models) and the rheological parameters of each model were determined

A Comprehensive Equilibrium Model for the Phosphonate Scale Inhibitor-Carbonate System including Coupled Adsorption/Precipitation (Γ/Π)

Inorganic scale deposition is one of the main flow assurance issues in hydrocarbon production, and injection systems, leading to significant loss in production and subsequent expense to mitigate. Scale Inhibitors (SI) are chemicals that are commonly used to prevent the inorganic scale from building up in the system. SIs are usually injected into the porous media, where they can react and be retained, and released back into the produced brine as the production commences. This in situ scale prevention method is known as “squeeze treatment”, and the lifetime of this process is determined when the SI concentration in the return fluid falls below the MIC (Minimum Inhibitor Concentration), where the SI is sufficiently effective at preventing or efficiently reducing scale formation.In this study, a general chemical equilibrium model has been developed to simulate the chemical reaction of phosphonate scale inhibitors and their retention in a carbonate system (calcite), in the presence of an aqueous phase containing free divalent cations. The model couples together the following processes (i) the carbonate system, (ii) speciation of the SI, modelled as a weak polyacid, HnA, (iii) the metal (Ca2+, Mg2+) binding – SI chelant interactions, (iv) phosphonate SI acid impurity reactions, (v) adsorption of the free and complex species to the rock surface and (vi) and finally, the precipitation of complex species (SI-Ca-Mg). To find the equilibrium conditions, charge balance and mass balances for key components in the system were considered, and combined utilizing reaction constants, i.e. equilibrium constants, stability constants, and solubility constants. This full equation set can be solved numerically to find the equilibrium concentration of all engaged species to characterize the equilibrium condition. To account for the adsorption and precipitation retention in this system, a coupled adsorption/precipitation (Γ/Π) isotherm has been presented and used for the first time. The coupled Γ/Π isotherm is a mathematical representation of the retention amount in the system that coupled adsorption and precipitation retention mechanisms are in action, which can scale up the retention results to other systems with different mass to volume ratios.To validate the proposed model, experimental results of a DETPMP-Calcite equilibrium system in NSSW were considered. The model and the experimental results were in good agreement demonstrating the reliability of the model. Furthermore, the reliability of the model in stoichiometry prediction of complexes, and distribution of species in different conditions was evaluated which confirmed the validity of the model