Investigation of well test behavior in gas condensate reservoir using single-phase pseudo-pressure function

Gas condensate reservoirs present complicated thermodynamic behavior when pressure falls below the dew point pressure, due to fluid dropout and change in the fluid composition. Condensate blockage in the near wellbore region reduces the well deliverability. Mixture composition change in the reservoir makes the interpretation of well tests in gas condensate reservoirs a serious challenge. In this study, at first the capillary number effect and Non-Darcy Flow on compositional simulation of gas condensate reservoirs were investigated and then well test analysis was carried out. The main objective of this work was to examine gas condensate well test analysis using single-phase gas pseudo-pressure and radial composite model assuming capillary number effect and Non-Darcy Flow. For this purpose some fluid samples were selected and results compared. Results indicate that estimation of reservoir properties below the dew point is in good agreement with actual input, particularly for lean fluid samples.     

葡萄花油层合理流压确定室内实验研究

低渗透油藏储层存在应力敏感的现象。本文通过室内物理模拟方法,研究岩心油相、水相渗透率随上覆压力损失及恢复规律,以及岩石弹塑性与渗透率保持规律之间关系的研究。模拟结果表明:天然岩心油相、水相渗透率均随着上覆压力的增大而降低,且岩心渗透率越低渗透率损失越大。在此基础上,确定了葡萄花油层投产阶段合理井底流压。     

Modeling phase equilibria for acid gas mixtures using the CPA equation of state. I. Mixtures with H2S

The Cubic‐Plus‐Association (CPA) equation of state is applied to a large variety of mixtures containing H₂S, which are of interest in the oil and gas industry. Binary H₂S mixtures with alkanes, CO₂, water, methanol, and glycols are first considered. The interactions of H₂S with polar compounds (water, methanol, and glycols) are modeled assuming presence or not of cross‐association interactions. Such interactions are accounted for using either a combining rule or a cross‐solvation energy obtained from spectroscopic data. Using the parameters obtained from the binary systems, one ternary and three quaternary mixtures are considered. It is shown that overall excellent correlation for binary mixtures and satisfactory prediction results for multicomponent systems are obtained. There are significant differences between the various modeling approaches and the best results are obtained when cross association is explicitly accounted for, especially using the cross‐association energy from independent experimental studies rather than from combining rules. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

The Effect of Fluoropolymer on Wettability Alteration of Sandstone at Elevated Temperatures

Gas condensate reservoirs are generally recovered using a pressure depletion drive. Gas can condensate into the liquid phase near the wellbore region when the reservoir pressure falls below the dew point pressure, which can kill gas deliverability. Wettability alteration is an effective means of overcoming this problem; core wettability can be altered from liquid-wet to gas-wet to alleviate the effect of condensate accumulation near the wellbore region. To establish the effect of fluoropolymer on wettability alteration in a gas-condensate reservoir, a gas-wetting alteration agent was synthesized by emulsion polymerization using different molar ratios of fluorine-containing monomers and acrylic monomers. FTIR and SEM were performed to analyze the structure of the gas-wetting agent. Contact angle measurements were used to assess surface alteration by the Owens two-liquid method. The effects of alteration agent concentration, salt concentration, pH and temperature on gas-wetting alteration were also evaluated. Results showed that the best molar ratio of fluoropolymer monomer to acrylic monomers was 1:2. The egg-like structure of the fluoropolymer latex on the core surface mainly contributes to gas-wetting alteration. The contact angles of brine and oil can be altered from 23° and 0° to 137° and 67° by 1 wt% FP-2 treatment, respectively. The surface free energy of the core was reduced from 67.52 to 1.66 mN/m. Moreover, the treated cores remain gas-wetting up to 100 g L^?1 of salt solution, 120 °C and within the pH range of 5–7. This novel gas-wetting alteration agent can be used to solve the problem of liquid blocking effects in gas condensate reservoirs and improve gas recovery significantly.     

富硫化氢酸性天然气相态行为的实验测定和模型预测

本文采用无汞抗硫ＰＶＴ装置，测定了三组富硫化氢酸性天然气混合物的Ｐ－Ｔ相包线数据，并比较了三个立方型状态方程：Ｓｏａｖｅ－Ｒｅｄｌｉｃｈ－Ｋｗｏｎｇ，Ｐｅｎｇ－Ｒｏｂｉｎｓｏｎ和Ｐａｔｅｌ－Ｔｅｊａ应用于酸性天然气泡／露点压力及ＰＶＴ数据的预测结果。对泡点压力的预测ＳＲＫ方程误差最小（１．１３％），而对露点压力的预测则ＰＴ方程误差最小（４．７７％）。应用多参数ＭＯＵ／ＧＲＩ方程预测富硫化氢酸性天然气压缩因子数据取得满意的结果，平均误差为０．６３５％。     

Wettability alteration of gas condensate reservoir rocks to gas wetness by sol–gel process using fluoroalkylsilane

Natural gas is becoming a very important energy source in recent years. A sharp reduction has been observed in gas deliverability in many low permeability gas reservoirs due to bottom‐hole pressure drops below the dew point pressure. It is an established fact that altering the wettability of reservoir rocks from liquid wetness to gas wetness could improve the gas deliverability. In this study, a new polymeric surfactant coating for altering the wettability of Sarkhun reservoir rocks was prepared by using a sol–gel process. Perfluorodecylsilane (PFDS) and triethoxysilane (TEOS) were used to obtain an inorganic‐organic network via hydrolysis and polycondensation reactions. The effect of this method was examined by various characterization tests such as FTIR, SEM, and EDX, static contact angle and imbibition tests for wettability alteration. The experimental results revealed that, the prepared polymeric network including the terminal fluorine groups were effective and provided sufficient repelling characteristics towards oil and water. Static contact angles were raised from 30 to 130° for water, and from <5 to 60° for condensate after sol–gel treatment. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

水醇烃体系相平衡模拟及其应用

采用CPA方程模拟了水、醇、烃多组分体系气液液三相平衡,与实验数据比较后可知,CPA方程能够较好地预测极性组分PVT特性和相平衡。并把CPA方程应用于汽提冷甲醇天然气脱水工艺的模拟计算,为工艺设计提供了必要的参考数据。     

Experimental determination and modeling of the phase behavior for the direct synthesis of dimethyl carbonate from methanol and carbon dioxide

This study focuses on the investigation of the phase behavior of mixtures relevant to the direct synthesis of dimethyl carbonate from methanol and carbon dioxide. The bubble points of corresponding quaternary mixtures of varying composition were experimentally determined. The Cubic-Plus-Association (CPA) equation of state was applied to model the phase behavior of the experimentally studied systems. In this regard, the CPA binary interaction parameters were estimated based on experimental data for the corresponding binary systems available in the literature, and subsequently the model was applied to predict the phase behavior of the multicomponent systems. It was shown that CPA is capable of predicting the phase behavior of such complex systems containing polar and associating components at high temperatures and pressures with reasonable accuracy considering the non-ideality of such mixtures. The results reveal P–T regions where the system can exist in one single phase and where it is multiphase, which can be used for further optimization not only of the chemical reaction itself but also subsequent product separation processes.     

On the predictive capabilities of CPA for applications in the chemical industry: Multicomponent mixtures containing methyl-methacrylate,dimethyl-ether or acetic acid

The predictive performance of the CPA (Cubic-Plus-Association) equation of state for applications relevant to the chemical industry is illustrated in this work. Three such applications inspired by industrial requests/interest are illustrated here, all of which involve aqueous multicomponent mixtures exhibiting vapor–liquid (VLE) and/or liquid–liquid (LLE) equilibrium. The first two cases include mixtures of methyl-methacrylate with acetone or methanol and dimethyl-ether with ethanol, respectively. In these two cases, the classical form of CPA is used. The third case involves aqueous mixtures with acetic acid, esters, ethers and alcohols, and in this case for water–acetic acid the CPA-Huron Vidal (CPA-HV) version of the model is used. For the latter binary mixture, new CPA-HV binary parameter sets are estimated using, among others, data for activity coefficients at infinite dilutions. The modeling approach is similar in all three cases, i.e. the binary parameters are solely fitted to binary data and thus all multicomponent calculations are considered predictions.It is shown that CPA correlations for binary systems are excellent in all cases using temperature independent parameters except for the acetic acid–water system for which different parameter sets at different temperatures can be recommended. Even with the use of CPA-HV mixing rules, modeling of the acetic acid–water system with few interaction parameters remains a challenging task. Excellent simultaneous VLE and LLE correlation is obtained for complex systems such as aqueous mixtures with ethers and esters. The multicomponent results are, with a few exceptions, very satisfactory, especially for the vapor–liquid equilibrium cases. For the demanding aqueous acetic acid–water containing systems, one parameter set is recommended at the end for modeling ternary or multicomponent mixtures containing acetic acid and water.     

基于人造岩心研究烟道气对高渗透油藏的驱油效果

高渗透油藏具有典型的三高特征,即"高渗透率、高产能、高丰度"。我国的高渗透油气资源所占比例较低,但众多学者并没有放弃对高渗透油藏提高采收率的研究,其后期开采阶段的采收率有待进一步提高。针对大部分油藏,基于前人使用各种类型的蒸汽,复合驱油本文基于人造高渗透岩心开展烟道气驱油实验,观察注入压力和注入PV数对最终油气采收率的影响。最终优选出最佳注入压力为10.1 MPa,最佳注入PV数为3.0 PV。     

Thermodynamic modeling of PVTx properties for several water/hydrocarbon systems in near-critical and supercritical conditions

Both the equation of state-excess Gibbs energy (EoS/G ^E ) model and the cubic plus association (CPA) equation of state (EoS) are compared in this study with respect to their accuracy in the correlation of PVTx for systems such as water/methanol, water/ethanol, water/benzene, water/toluene, water/methane, water/n-butane, water/n-pentane, water/n-hexane, water/heptane, and water/octane, in supercritical conditions within temperature and pressure ranges of (573–698 K) and (7.0–276.0 MPa), respectively. In the proposed EoS/G ^E model, Peng-Robinson (PR) equation of state, linear combination Vidal-Michelsen (LCVM) and Wong-Sandler (WS) mixing rules in conjunction with UNIQUAC activity coefficient model were used. Correlation of both CPA and EoS/G ^E models was evaluated by comparing the results with the experimental data. Average absolute relative deviation (AARD) for WS, LCVM, and CPA was found to be 2.99, 11.11 and 5.14%, respectively, indicating better correlation of WS model with the experimental data.     

二氧化碳在CH4+CO2+N2/C2H6三元系中的结霜温度计算

含CO₂的天然气体系在历经低温工艺时,由于CO₂的三相点温度(216.55 K)较高,容易凝华结霜产生固体CO₂,因而有必要对CO₂在天然气中的结霜温度进行计算。根据气固相平衡原理,分别采用道尔顿分压定律、PR状态方程对CO₂在CH₄-CO₂-N₂和CH₄-CO₂-C₂H₆三元系中的结霜温度进行了计算。此外,还采用HYSYS软件对CO₂的结霜温度做了相应的计算。将3种方法的计算结果和实验结果进行了比较,结果表明3种方法在预测三元系中CO₂的结霜温度时,都具有良好的精度。其中,PR状态方程法和HYSYS法的精度略高于道尔顿分压定律法;道尔顿分压定律法虽精度最低,但计算最简单,且也能获得满意的精度,可做工程快速估算使用。     

Effect of Hydrocarbon and Non‐Hydrocarbon Gas Injection on the Interfacial Tension of a Gas Condensate System

Experimental results of interfacial tension (IFT) of condensate‐brine‐gas systems over a pressure range of 1000 to 8000 psi and a temperature range of 95 to 160 °C are presented. High‐pressure high‐temperature video‐enhanced pendent drop tensiometry was established to capture drop images for IFT measurements at various reservoir thermodynamic conditions. This paper serves as a building block to the essential practical understanding of the surface effects associated with improved condensate recovery from gas condensate reservoirs by gas injection. This understanding is critical for ascertaining gas injectivity, displacement and trapping in the pore spaces, and potential geological storage of CO₂.     

阿姆河右岸水平气井改进一点法公式推导及应用

一般来讲水平气井较垂直气井测试产量高、测试压差小,常规一点法计算水平气井无阻流量误差较大,无法准确评价其产能及指导其合理配产。通过文献调研发现2005年冯曦等人给出了垂直气井基于渗透率变化的改进一点法产能公式,本文在此基础上推导出水平气井改进一点法产能公式,并根据阿姆河右岸气田水平气井的实际测试情况,进行该进一点法产能公式计算无阻流量,与二项式产能公式计算无阻流量对比,平均绝对误差在10%以内,符合现场应用的需要,对水平气井产能研究具有一定的借鉴意义。     

柯克亚凝析气田气井增产技术

新疆柯克亚凝析气田勘探初期遭受了3口喷井的破坏和其后近20年的衰竭式开采,地层压力大幅度下降,地层反凝析现象严重,严重污染了井筒周围的储层,造成渗流阻力增大,致使多口气井停产或无法正常生产,影响气藏的整体开发效果。针对此现状,实施了气井增产配套技术,主要有:单井注气吞吐、高压天然气间歇气举、排液采气、优化管柱,取得了显著增产效果,为同类气田高效开采,提高采收率提供了有效途径。     

Study on Wettability Variation for Removing Liquid Block in Condensate Gas Reservoir

Condensate liquid in porous media can prevent gas from exiting when the pressure is lower than the dew point pressure in the condensate gas reservoir. This can lead to liquid block and sharp decreases in gas yield. In this work, super-amphiphobic materials were used to remove the liquid block and recover the product. The experiments indicated that this method can effectively remove the damage of liquid block and improve the productivity of the gas well.     

撞击流反应器用于甲醇合成反应

撞击流反应器用于气液固三相甲醇合成反应可以充分发挥其优良的传热、传质性能。在撞击流反应器内,催化剂浆料经喷嘴雾化后成微米尺度的液滴,气液相间接触面积远大于其他三相合成反应器。考察了温度、压力、气体流量、浆料循环量以及喷嘴个数对甲醇合成反应的影响,结果表明,当压力从3.8 MPa上升到5 MPa时,反应器的时空产率增长了近1倍,气体流量达22.4 L·min^-1后时空产率几乎不再变化,增加浆料循环量以及在同一循环量下采用多喷嘴对置都可以增加催化剂时空产率。同时,与固定床、搅拌釜和浆态鼓泡床甲醇合成进行了对比,结果表明,在低空速下撞击流反应器与其他反应器时空产率相当,而在高空速下要优于其他反应器。     

Development of a neural fuzzy system for advanced prediction of dew point pressure in gas condensate reservoirs

Dew point pressure is one of the most critical quantities for characterizing a gas condensate reservoir. So, accurate determination of this property has been the main challenge in reservoir development and management. The experimental determination of dew point pressure in PVT cell is often difficult especially in case of lean retrograde gas condensate. Empirical correlations and some equations of state can be used to calculate reservoir fluid properties. Empirical correlations do not have ability to reliable duplicate the temperature behavior of constant composition fluids. Equations of state have convergence problem and need to be tuned against some experimental data. Complexity, non-linearity and vagueness are some reservoir parameter characteristic which can be propagated simply by intelligent system. With the advantage of fuzzy sets in knowledge representation and the high capacity of neural nets (NNs) in learning knowledge expressed in data, in this paper a neural fuzzy system(NFS) is proposed to predict dew point pressure of gas condensate reservoir. The model was developed using 110 measurements of dew point pressure. The performance of the model is compared against performance of some of the most accurate and general correlations for dew point pressure calculation. From the results of this study, it can be pointed out that this novel method is more accurate and reliable with the mean square error of 0.058%, 0.074% and 0.044% for training, validation and test processes, respectively.     

An electrolyte CPA equation of state for mixed solvent electrolytes

Despite great efforts over the past decades, thermodynamic modeling of electrolytes in mixed solvents is still a challenge today. The existing modeling frameworks based on activity coefficient models are data‐driven and require expert knowledge to be parameterized. It has been suggested that the predictive capabilities could be improved through the development of an electrolyte equation of state. In this work, the Cubic Plus Association (CPA) Equation of State is extended to handle mixtures containing electrolytes by including the electrostatic contributions from the Debye–Hückel and Born terms using a self‐consistent model for the static permittivity. A simple scheme for parameterization of salts with a limited number of parameters is proposed and model parameters for a range of salts are determined from experimental data of activity and osmotic coefficients as well as freezing point depression. Finally, the model is applied to predict VLE, LLE, and SLE in aqueous salt mixtures as well as in mixed solvents. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2933–2950, 2015