低渗油藏CO_2驱中注采方式优化设计

低渗油藏储层致密,衰竭与注水效果差,由于CO_2具有易流动、降黏、体积膨胀的特点,在解决低渗透油藏开发方面表现出独特的优势.讨论了低渗油藏CO_2驱中的注采方式,分析了目前常用的连续注气、水气交替和生产井控制等注采方式的优缺点,提出应综合考虑原油采收率、CO_2埋存量、经济效益及其在低渗油藏中的适用性.并针对以上方法的不足提出了另外3种改进注采方式,通过油藏工程研究、典型模型和实例油藏的数值模拟进行测试分析,表明改进的依据生产井气油比和平均静压两种指标实施开关井控制的CO_2驱注采方法能够满足低渗油藏注气能力需要,且具有开发周期短、油藏采收率高、CO_2埋存潜力大等特点,油田实施简易,能够取得较好经济、社会效益.     

Reservoir simulation of CO2 sequestration pilot in Frio brine formation,USA Gulf Coast

Reservoir simulation studies were performed to investigate compositional effects between aquifer fluid (brine) and injected supercritical CO₂ during the sequestration process in the Frio brine formation. Accurate data calibrations of CO₂ solubility and density, as well as brine density and viscosity, were performed. Hysteresis relative permeability was taken into consideration to account for the effect of trapped gas in the aquifer. In addition, real aquifer data obtained from the test site were used in order to characterize the Frio aquifer.     

Wettability Modification of Fractured Carbonates Using Sodium Metaborate Part II: History Match Results and Sensitivity Simulations

Abstract

Chemical-based wettability modification has become important for the worldwide abundance of fractured carbonates with the potential to enhance water imbibition to expel more oil from a matrix to the fractures. A systematic experimental and modeling approach on the combined benefit of wettability alteration for enhanced water imbibition and interfacial tension reduction is presented. Brine, alkali, and alkali–surfactant solutions are injected sequentially to improve oil recovery from a fractured mixed-wet carbonate core. The experiment was successfully modeled with a 3D chemical flooding reservoir simulator with wettability alteration capability. Part I discussed the laboratory results and presented the modeling approach and the waterflood history match results. The history match procedure and results for wettability modification using an alkali agent and interfacial tension (IFT) reduction with surfactant are discussed in this article. Sensitivity simulations to some key parameters are also presented.     

An Automatic History Matching Module with Distributed and Parallel Computing

Abstract

The data assimilation process of adjusting variables in a reservoir simulation model to honor observations of field data is known as history matching and has been extensively studied for a few decades. However, limited success has been achieved due to the high complexity of the problem and the large computational effort required in the real fields. Successful applications of the ensemble Kalman filter (EnKF) to reservoir history matching have been reported in various publications. The EnKF is a sequential method: once new data are available, only these data are used to update all the unknown reservoir properties while previous geological information is unused directly. In this method, multiple reservoir models rather than one single model are implemented, and each model is called a member. Conventionally, the impact of each member on the updating is equally treated. Another approach is the weighted EnKF. During the updating, the method weighs the contribution of each member through the comparison between the simulation response and the measurements. Better matching performance has been found in the weighted EnKF than in the conventional EnKF. To improve computational efficiency, two-level high-performance computing for reservoir history matching process is implemented in this research, distributing ensemble members simultaneously while simulating each member in a parallel style.

An automatic history-matching module based on the weighted EnKF and high-performance computing is developed and validated through a synthetic case operating from primary, waterflooding to flooding of water alternating with gas. The study shows that the weighted EnKF improves the matching results, and the high-performance computing process significantly reduces the history matching execution time.     

液氮磨料射流破碎高温花岗岩机理

液氮磨料射流是一种高效的破碎干热岩方式。为进一步探究其破岩机理,开展液氮磨料射流喷射高温花岗岩室内实验。从宏观角度分析岩石破碎形式、射流孔眼形态及表面特征,从微观角度分析断裂面形貌和微裂缝分布等,探究液氮磨料射流破碎高温岩石特征。同时,开展磨料水射流和氮气磨料射流破岩实验作为对照。实验结果表明,液氮磨料射流形成的孔眼形状不规则,表面凹凸不平,且破碎体积明显大于磨料水射流和氮气磨料射流。扫描电镜实验显示,低温、冲击载荷作用下,在孔眼壁面和孔眼附近区域生成大量微裂缝,其主要断裂方式为拉伸、剪切作用下岩石的脆性断裂,表现为穿晶断裂和沿晶断裂。理论分析和数值模拟研究表明,液氮低温作用对岩石造成损伤,而热应力、磨料冲击载荷和流体水楔作用在损伤岩石基础上主要以剪切和拉伸两种方式破碎岩石。     

Application of a Coupled Wellbore/Reservoir Simulator to Estimate Accumulated Liquid Phase in Gas Wells

Abstract

Knowledge of the phase distribution and liquid accumulation in gas wells is very important in determining the restrictions that may exist for the inflow from the formation. It is also critical to determine if the flow rate of a well is itself sufficient to remove the loaded liquid phase or if other techniques should be applied. In this article, we used a developed non-isothermal transient multiphase wellbore/reservoir simulator to model liquid accumulation in gas wells. The simulator can be used as a tool to predict the amount of loaded liquid as a function of well flow rate and to design new flow strings to remove accumulated liquid.     

A Weighted Ensemble Kalman Filter for Automatic History Matching

Abstract

The ensemble Kalman filter (EnKF) performs the initial sampling, forecasting, and assimilation steps for automatic history matching in the petroleum industry. It tunes multiple members sequentially and updates the statistical mean and variance of the model. Many applications have been reported in various publications. The forecasting step is implemented by running the reservoir model simulator. In the assimilation equation, the ensemble mean is calculated through equally weighting all the members. Therefore, the contribution factor to the mean from each member is the same. This paper proposes a modified assimilation equation by introducing a weighting factor for each ensemble member. Both the proposed weighted EnKF and the traditional EnKF are applied to a modified field case of a complex seventeen-layer reservoir. The performances of the weighted EnKF on production history match, forecasting, and field permeability match are better than those from the traditional EnKF. In addition, we investigate the impact of geological uncertainty in the initial ensemble generation on the final matching results. Two scenarios which have the same semivariogram as the reference field are implemented, and their results show that the initial geological information is important to the history matching performance.     

Axially symmetric compositional simulation of formation tester measurements

This paper describes the development, testing, and successful application of a new compositional code for the numerical simulation of oil-based mud invasion and formation tester measurements that involve arbitrary miscibility between oil-based mud and native oil. The simulator assumes axially symmetric variations of petrophysical properties as well as axially symmetric flow-rate sources and boundary conditions. However, there are no restricting assumptions to the degree of miscibility between the fluids involved in the simulations. We solve the time–space evolution of component concentration with a time-marching implicit pressure explicit concentration (IMPEC) scheme. This method of solution considers the complete equations of state and implements flash calculations to describe the thermo-dynamical evolution of the various compositional phases due to space–time variations of pressure and concentration.Simulations described in this paper consider the process of oil-based mud–filtrate invasion into reservoirs containing mixtures of connate water and oil. Subsequently, we simulate formation tester measurements by enforcing fluid withdrawal through the dual-packer section of the tester. Measurements consist of fluid pressure, fractional flow rates, fluid density, and fluid viscosity. Examples of application include homogenous and multi-layer formations as well as a capillary transition zone. Comparison of simulation results against those obtained with a commercial code confirms the efficiency, accuracy, and reliability of our method of solution.Sensitivity analysis indicate that time evolution of fractional flow rates, fluid density, and fluid viscosity measured with the formation tester remain influenced by the petrophysical properties of the formation, volume of mud–filtrate invasion, and by saturation-dependent rock–fluid properties (relative permeability and capillary pressure). The simulations described in this paper provide suitable guidelines for the acquisition of clean samples of in-situ formation fluids in the presence of invasion and heterogeneous conditions of petrophysical and rock–fluid properties.