Experimental investigation of effect of asphaltene deposition on oil relative permeability,rock wettability alteration,and recovery in WAG process

Asphaltene deposition is considered to be one of the most problems during oil productions. This work describes the effect of asphaltene precipitation and deposition on relative permeability of reservoir rock during water alternating gas (WAG) injection process. The main objective of this work is experimental investigating of relative permeability change of reservoir fluid due to asphaltene deposition on application of WAG process by use of core flood setup. Result of this paper investigate the relative permeability change during WAG process with different asphaltene content that help to make better development decisions for a reservoir with fluid with specific asphaltene content.     

超临界CO2 处理对乳状液稳定性的影响机理研究

超临界CO₂(scCO₂)混相驱在提高原油采收率的同时,也显著改变采出原油乳液的性质。利用自主研发的CO₂-原油混相装置在模拟地层条件下对长庆原油进行混相处理,分别使用流变仪、电导率仪和显微镜研究了混相处理前后长庆原油及其W/O 乳液的流变性、稳定性和微观形貌。实验结果表明,scCO₂ 处理改变了长庆原油的组成,破坏了沥青质溶剂化层结构,使得失去保护的沥青质胶粒更易吸附于油水界面;scCO₂ 处理也使得析出的蜡晶尺寸更加细小,数量增加,这将导致乳液黏度显著增大。上述变化导致scCO₂ 处理后W/O 原油乳液的水滴粒径变小、分布更加均匀,宏观表现为乳液体系的流动性恶化、稳定性增强。     

稳定剂对石油沥青质体系粘度的影响

采用毛细管粘度计考察了稳定剂对石油沥青质溶液粘度性质的影响。结果表明,沥青质以柔软可塑的球形存在,在无稳定剂存在下,沥青质溶液体系的稳定性主要取决于沥青质的颗粒大小;对油酸-正庚烷-渣油体系,稳定剂浓度增加,体系粘度先增大(相对粘度增大8.2%)后减小,最后趋于稳定,说明稳定剂在低浓度时对沥青质起分散作用,而高浓度时起聚集作用;在油酸质量浓度为100 mg/L时,油酸-正庚烷-渣油体系的相对粘度比油酸-正庚烷(体积分数40%)-甲苯-渣油体系的相对粘度高8.5%,说明正庚烷的加入使渣油中的沥青质发生明显的聚集;溶液粘度受稳定剂酸碱性影响不大。     

Determination of asphaltene precipitation using a CPA equation of state

Asphaltene precipitation during natural depletion and miscible gas injection is a common problem in oilfields throughout the world. Therefore, predicting asphaltene phase behavior through thermodynamic modeling may help to control its precipitation and reduce the associated problems. In this work, a new modified CPA equation of state (EoS) was used to model asphaltene precipitation. This equation is based on a combination of a new physical part and the Wertheim association term.

The results of the new model were compared with the experimental data of five oil samples. The results showed that this modified CPA EoS can predict asphaltene precipitation with good accuracy.     

Modification of a thermodynamic model and an equation of state for accurate calculation of asphaltene precipitation phase behavior

In this study, DPTG (Dashtizadeh-Pazuki-Taghikhani-Ghotbi) equation of state has been modified for calculation of phase behavior of fluids and solubility parameter. The accuracy of the modified EOS has been proved by estimation of the properties of some hydrocarbons such as densities of methane and condensate gases, vaporization enthalpy, sublimation pressure, compressibility factor and comparison of the obtained results with the results of the present equations of state such as NJ (Nasrifar-Jalali), ZMJL (Zhi-Meiren-Jun-Lee) and PR (Peng-Robinson). Then, the Flory-Huggins model has been modified and asphaltene precipitation phase behavior at different ratios of solvents in the crude oil has been predicted by the modified EOS and the developed Flory-Huggins model. Comparison of the obtained results with the experimental data of asphaltene precipitation and the calculated ones by the main Flory-Huggins model shows the accuracy of the developed model.     

Microstructural study of asphaltene precipitated with methylene chloride and n-hexane

This work presents a study of the microstructure, molecular structure and elemental composition of asphaltene precipitated from vacuum residue using a solvent mixture. The infrared spectroscopy (FTIR) results show vibration bands of functional groups such as aromatic C-H (4 adj H and 1 adj H) and sulfoxide (C₂SO). Low vacuum scanning electron microscopy (LV-SEM) reveals a highly porous and a smooth surface asphaltene. C, S and V are the main elements identified by energy dispersive X-ray spectroscopy (EDS) analysis, though some variations in concentration were observed between the porous and the smooth surface asphaltene. Transmission electron microscopy (TEM) analysis shows that asphaltenes are constituted by nanometric particles (micelles) of ∼50 nm in diameter. These particles conform agglomerates (flocs) from ∼350 to ∼550 nm in size, some of them in layer arrangement with a tendency to graphitize. These results reveal important information about flocculation processes of the asphaltene.     

多孔滤膜抽滤法测定原油沥青质含量

对测定原油沥青质含量的3种分离方法(离心法、抽滤法、过滤法)进行对比,观察到抽滤法在安全健康、效率及重复性等方面具有明显优势。采用激光纳米粒度分析仪对3种分离方法的残液进行了粒度分析,结果表明,过滤法将导致较多的沥青质颗粒的损失,造成测量结果偏小。在此基础上,对抽滤法测试流程中涉及的剂油比、样品静置时间、取样量等影响因素进行优选,确定出适宜剂油比为40 mL/g、静置时间30 min、取样质量1.0g。与SY/T 7550—2004标准方法相比,采用多孔滤膜抽滤法测定原油沥青质含量,推荐的参数合理,测试精度较高。     

Solution techniques for population balance equation: A case study for asphaltene aggregation

Population balance equation is widely used in modeling of particulate processes. In this work, the enlargement of asphaltene particles in a synthetic heptane-toluene mixture (Heptol) was experimentally investigated in a static mode and then modeled by using PBE. Aggregation is considered as sole responsible mechanism for size evolution. Three solution methods including two discretization methods, modified Hounslow (MH) method and Kumar cell average technique (KCAT), and one moment method, quadrature method of moments (QMOM), are considered. The simulation results were compared with experimental data to evaluate each method. The results of simulations indicate that moment method offers higher accuracy and less computational expense respect to discretized methods in prediction of asphaltenes aggregation. In the case of considering fractal structure, both methods inaccurately predicted the number and average diameter of asphaltene aggregates.     

An investigation of stabilization and inhibition strength of the asphaltene inhibitors by viscometric method

Using inhibitors is one of the methods to prevent asphaltene formation. In the present work, we investigated the effects of three types of inhibitors on the onset of asphaltene precipitation using the viscometric method. Also in this study, a new concept called “effective adsorption point” of the inhibitor was proposed in order to determine the stabilization (dispersion) strength, by measuring the shear effects of asphaltene aggregates. The results showed that the amount of adsorbed inhibitor on the surface of asphaltene micelles, together with stabilization strength, started to increase with increasing inhibitor concentration. The results also revealed that there is a strong agreement between the calculated volume fraction of suspended particles and the effective adsorption point.     

Ultrasound cavitation technique for up-gradation of vacuum residue

Generally, upgradation of the petroleum residue to valuable product is done through the catalytic and thermal cracking using very high temperature and pressure. The ultrasound assisted cavitation is the novel technique to intensify the cracking of asphaltene present in the vacuum residual feedstock.The up-gradation of residue was carried out with application of low frequency (24 kHz), high intensity ultrasound under atmospheric pressure and ambient temperature in a batch reactor.In the present work, vacuum residue, having high viscosity was subjected to acoustic cavitation for different reaction times (15 min to 90 min) and with different probe diameters at ambient temperature and pressure. The effect of ultrasound on the upgradation of residue (asphaltene degradation) has been studied with surfactant as emulsifier as well as without surfactant. Also, the effect of acoustic cavitation has been studied on the physico-chemical properties of residue.The study revealed that the asphaltene content of the vacuum residue decreased from 13.5 (initial asphaltene present in residue) to 7% (wt.%). It has been also observed that the physico-chemical properties of residue reduced with the influence of ultrasound energy.