Crystallisation Fouling Of Mixed Salts During Convective Heat Transfer And Sub-Cooled Flow Boiling Conditions

The mechanisms of mixed salt crystallisation fouling on heat transfer surfaces have been investigated for convective and sub-cooled flow boiling heat transfer. Effects of various operating parameters such as solution composition and hydrodynamics of the system, on crystallisation fouling of mixtures of calcium sulphate and calcium carbonate have been studied experimentally. The results of the experiments were used to develop a mechanistic model for prediction of fouling resistances. Model predictions were compared with the measured experimental data when calcium sulphate and calcium carbonate form and deposit on the heat transfer surface, simultaneously. Deviations ranging from 6% to 25% were observed which confirm the suitability of the model. Finally, the crystalline samples were analysed using Scanning Electron Microscopy, X-Ray Diffraction and Ion Chromatography techniques. Fractal analysis performed on Scanning Electron Microscopy photographs of the deposits was used to quantify deposit characteristics by introducing the fractal dimension as a new characteristic quantit

Estimation of minimum miscibility pressure of varied gas compositions and reservoir crude oil over a wide range of conditions using an artificial neural network model

Minimum miscibility pressure (MMP) is a key variable for monitoring miscibility between reservoir fluid and injection gas. Experimental and non-experimental methods are used to estimate MMP. Available miscibility correlations attempt to predict the minimum miscibility pressure for a specific type of gas. Here an artificial neural network (ANN) model is applied to a dataset involving 251 data records from around the world in a novel way to estimate the gas-crude oil MMP for a wide range of injected gases and crude oil compositions. This approach is relevant to sequestration projects in which injected gas compositions might vary significantly. The model is correlated with the reservoir temperature, concentrations of volatile (C1 and N2) and intermediate (C2, C3, C4, CO2 and H2S) fractions in the oil (Vol/Inter), C5+ molecular weight fractions in the oil and injected gas specific gravity. A key benefit of the ANN model is that MMP can be determined with reasonable accuracy for a wide range of oil and gas compositions. Statistical comparison of predictions shows that the developed ANN model yields better predictions than empirical-correlation methods. The ANN model predictions achieve a mean absolute percentage error of 13.46%, root mean square error of 3.6 and Pearson's correlation coefficient of 0.95. Sensitivity analysis reveals that injected gas specific gravity and temperature are the most important factors to consider when establishing appropriate miscible injection conditions. Among the available published correlations, the Yellig and Metcalfe correlation demonstrates good prediction performance, but it is not as accurate as the developed ANN model.Cited as: Choubineh, A., Helalizadeh, A., Wood, D.A. Estimation of minimum miscibility pressure of varied gas compositions and reservoir crude oil over a wide range of conditions using an artificial neural network model. Advances in Geo-Energy Research, 2019, 3(1): 52-66, doi: 10.26804/ager.2019.01.0

Mixed salt crystallisation fouling

The main purpose of this investigation was to study the mechanisms of mixed salt crystallisation fouling on heat transfer surfaces during convective heat transfer and sub-cooled flow boiling conditions. To-date no investigations on the effects of operating parameters on the deposition of mixtures of calcium sulphate and calcium carbonate, which are the most common constituents of scales formed on heat transfer surfaces, have been reported. As part of this research project, a substantial number of experiments were performed to determine the mechanisms controlling deposition. Fluid velocity, heat flux, surface and bulk temperatures, concentration of the solution, ionic strength, pressure and heat transfer surface material were varied systematically. After clarification of the effect of these parameters on the deposition process, the results of these experiments were used to develop a mechanistic model for prediction of fouling resistances, caused by crystallisation of mixed salts, under convective heat transfer and sub-cooled flow boiling conditions. It was assumed that the deposition process of calcium sulphate and calcium carbonate takes place in two successive events. These events are the combined effects related to transport phenomena and chemical kinetics. The effect of the extra deposition created on the heat transfer surface due to sub-cooled flow boiling was considered by inclusion of an enhancement factor. The newly developed model takes into account the effects of all important parameters on scaling phenomena and also considers the simultaneous precipitation and competition of various minerals in the scale formation process. Model predictions were compared with the measured experimental data when calcium sulphate and calcium carbonate form and deposit on the heat transfer surface simultaneously. While deviations ranging from 6% to 25% between model predictions and measured experimental data can be considered good in the context of such a complex process

The impacts of gas impurities on the minimum miscibility pressure of injected CO2-rich gas–crude oil systems and enhanced oil recovery potential

Abstract An effective parameter in the miscible-CO2 enhanced oil recovery procedure is the minimum miscibility pressure (MMP) defined as the lowest pressure that the oil in place and the injected gas into reservoir achieve miscibility at a given temperature. Flue gases released from power plants can provide an available source of CO2, which would otherwise be emitted to the atmosphere, for injection into a reservoir. However, the costs related to gas extraction from flue gases is potentially high. Hence, greater understanding the role of impurities in miscibility characteristics between CO2 and reservoir fluids helps to establish which impurities are tolerable and which are not. In this study, we simulate the effects of the impurities nitrogen (N2), methane (C1), ethane (C2) and propane (C3) on CO2 MMP. The simulation results reveal that, as an impurity, nitrogen increases CO2–oil MMP more so than methane. On the other hand, increasing the propane (C3) content can lead to a significant decrease in CO2 MMP, whereas varying the concentrations of ethane (C2) does not have a significant effect on the minimum miscibility pressure of reservoir crude oil and CO2 gas. The novel relationships established are particularly valuable in circumstances where MMP experimental data are not available

Investigation of Underground Sour Gas Storage in a Depleted Gas Reservoir

Underground Gas Storage (UGS) involves storage of large quantities of natural gas to support the natural gas demand in domestic, commercial and industrial areas. Storage of sour gas can be advantageous from economic standpoint, as it reduces treatment costs and increases the potential of production from shared reservoirs. This paper investigates feasibility of UGS in one of Iranian depleted fractured gas condensate reservoirs. Compositional simulation was employed to build dynamic reservoir model, develop the history matching phase of the reservoir and construct Injection/Withdrawal (I/W) cycles. One sweet gas stream and three sour gas streams with different compositions were tested for storage into reservoir during summer season. Results of simulation showed that presence of H2S and CO2 in the injected gas stream improves condensate production. Condensate Production Enhancement (CPE), defined as the percentage of condensate recovery increase due to sour gas injection relative to the sweet gas injection, was calculated for different compositions of storage gas. Also, Condensate Holding Ratio (CHR), defined as the ratio of condensate in the withdrawn sour gas to that in the withdrawn CH4, was estimated for different storage gas compositions. Results showed that CPE has a higher rate in earlier cycles and declines at later cycles. CHR is higher for sour gas storage compared to sweet gas. Furthermore, heating value of produced gas was calculated in all I/W cycles and compared with heating value of injected gas. It was indicated that difference between heating value of produced and injected gas increases with increase of H2S and CO2 content of the injected gas. Also, it was found that the reservoir has lower pressure rise at the end of I/W cycles in the case of underground sour gas storage compared to sweet gas storage. The presence of acid gas components decreases the z-factor of injected gas stream resulting in smaller difference between z-factors of injected gas and reservoir fluid

Investigation of Underground Sour Gas Storage in a Depleted Gas Reservoir

Underground Gas Storage (UGS) involves storage of large quantities of natural gas to support the natural gas demand in domestic, commercial and industrial areas. Storage of sour gas can be advantageous from economic standpoint, as it reduces treatment costs and increases the potential of production from shared reservoirs. This paper investigates feasibility of UGS in one of Iranian depleted fractured gas condensate reservoirs. Compositional simulation was employed to build dynamic reservoir model, develop the history matching phase of the reservoir and construct Injection/Withdrawal (I/W) cycles. One sweet gas stream and three sour gas streams with different compositions were tested for storage into reservoir during summer season. Results of simulation showed that presence of H2S and CO2 in the injected gas stream improves condensate production. Condensate Production Enhancement (CPE), defined as the percentage of condensate recovery increase due to sour gas injection relative to the sweet gas injection, was calculated for different compositions of storage gas. Also, Condensate Holding Ratio (CHR), defined as the ratio of condensate in the withdrawn sour gas to that in the withdrawn CH4, was estimated for different storage gas compositions. Results showed that CPE has a higher rate in earlier cycles and declines at later cycles. CHR is higher for sour gas storage compared to sweet gas. Furthermore, heating value of produced gas was calculated in all I/W cycles and compared with heating value of injected gas. It was indicated that difference between heating value of produced and injected gas increases with increase of H2S and CO2 content of the injected gas. Also, it was found that the reservoir has lower pressure rise at the end of I/W cycles in the case of underground sour gas storage compared to sweet gas storage. The presence of acid gas components decreases the z-factor of injected gas stream resulting in smaller difference between z-factors of injected gas and reservoir fluid

Investigation of Underground Sour Gas Storage in a Depleted Gas Reservoir

Underground Gas Storage (UGS) involves storage of large quantities of natural gas to support the natural gas demand in domestic, commercial and industrial areas. Storage of sour gas can be advantageous from economic standpoint, as it reduces treatment costs and increases the potential of production from shared reservoirs. This paper investigates feasibility of UGS in one of Iranian depleted fractured gas condensate reservoirs. Compositional simulation was employed to build dynamic reservoir model, develop the history matching phase of the reservoir and construct Injection/Withdrawal (I/W) cycles. One sweet gas stream and three sour gas streams with different compositions were tested for storage into reservoir during summer season. Results of simulation showed that presence of H2S and CO2 in the injected gas stream improves condensate production. Condensate Production Enhancement (CPE), defined as the percentage of condensate recovery increase due to sour gas injection relative to the sweet gas injection, was calculated for different compositions of storage gas. Also, Condensate Holding Ratio (CHR), defined as the ratio of condensate in the withdrawn sour gas to that in the withdrawn CH4, was estimated for different storage gas compositions. Results showed that CPE has a higher rate in earlier cycles and declines at later cycles. CHR is higher for sour gas storage compared to sweet gas. Furthermore, heating value of produced gas was calculated in all I/W cycles and compared with heating value of injected gas. It was indicated that difference between heating value of produced and injected gas increases with increase of H2S and CO2 content of the injected gas. Also, it was found that the reservoir has lower pressure rise at the end of I/W cycles in the case of underground sour gas storage compared to sweet gas storage. The presence of acid gas components decreases the z-factor of injected gas stream resulting in smaller difference between z-factors of injected gas and reservoir fluid