Streamline-Based History Matching Constrained to Reservoir Geostatistics Using Gradual Deformation Technique

Abstract

A new and general procedure for history matching that uses streamline simulation and a gradual deformation technique has been proposed. Streamline trajectories define the major flow paths and help the algorithm to modify the reservoir model only in the regions that cause the mismatch between simulation results and field observations. The use of a gradual deformation technique enables the algorithm to remain constrained to reservoir geostatistics. It also reduces the number of independent variables in the optimization problem. In our algorithm, effective conductivities are defined along each streamline. The effective streamline conductivities are then adjusted using the values of measured and computed breakthrough times of individual streamlines. Then an intermediate objective function is defined to minimize the difference between adjusted (desired) and computed effective streamline conductivities. The algorithm continues until a satisfactory match is obtained. In order to examine the quality of our history matching procedure, it is applied to a synthetic reservoir.     

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.     

Estimation of Fracture–Matrix Transport Properties from Saturation Profiles Using a Multivariate Automatic History Matching Method

Abstract

This study focuses on the development and implementation of a numerical model of multiphase flow in a fractured core sample by describing the capillary pressure–relative permeability characteristics. An automated history matching approach is proposed to determine relative permeability and capillary pressure curves simultaneously for both matrix and fracture consistent with a core flood reservoir model performance, which relies on a commercial reservoir simulator coupled with an optimization protocol. The results indicate that the proposed approach successfully predicts relative permeability and capillary pressure curves of a fractured core sample and provides a foundation for field-scale history matching with simultaneous estimation of transport properties.     

流动单元约束的油藏数值模拟研究

油藏数值模拟在油田开发方案的编制和确定、油田开采中生产措施的调整和优化、剩余油形成与分布以及提高油藏采收率方面,已逐渐成为一种不可欠缺的研究手段。油藏数值模拟的精度主要受油藏地质模型的精细程度和模拟模型的求解精度的影响。从提高油藏地质模型精度入手,将流动单元与油藏数值模拟相结合,通过利用流动单元细分模拟层系和针对不同的流动单元选取相应的相对渗透率曲线,提高油藏数值模拟的精度。模拟结果表明,流动单元约束的油藏数值模拟模型具有初始拟合程度高、模型修改程度低、能够更精确的反映层内和平面剩余油分布的特点。     

Experimental Evaluation of the Petrophysical Algorithm in an Integrated Flow Model

Abstract

An experimental apparatus was designed to simultaneously measure fluid flow rates and high-frequency (ultrasonic) elastic wave velocities. The measured fluid production and elastic wave velocity data were compared to integrated flow model (IFM) calculations. An IFM is a flow simulator with a petrophysical model that can calculate seismic attributes using reservoir and fluid properties. The petrophysical algorithm is an extension of Gassmann's equation that lets moduli depend on effective pressure, porosity, and clay fraction. A new set of correlation coefficients for the petrophysical algorithm was obtained by matching high-frequency measurements.     

INTERPRETING BIOSTRATIGRAPHICAL DATA USING FUZZY LOGIC: THE IDENTIFICATION OF REGIONAL MUDSTONES WITHIN THE FLEMING FIELD, UK NORTH SEA

The Fleming gas‐condensate field, located on the eastern flank of the Central Graben, UK North Sea, is an elongate stratigraphic pinch‐out whose reservoir is composed of stacked turbidite sandstones of the lower Palaeogene Maureen Formation. The sandstones have a sheet‐like geometry with each sandstone lobe being partially offset into the swales of the preceding lobes. In such depositional environments, the understanding of lateral and vertical sandstone connectivity, a major uncertainty in reservoir modelling and well planning and production strategies, depends upon the choice of depositional model that is applied and the lateral continuity of pelagic mudstones. Previously published work defined a model, based on variations in the composition of agglutinated foraminiferal populations, that could be used to derive a qualitative measure of the level of pelagic influence within mudstones interbedded with turbidite sandstones. It was considered that mudstones with a high pelagic influence are likely to be more laterally extensive than those with a low pelagic index. A fuzzy logic workflow was constructed using this model and was applied to the Fleming field in order to identify laterally persistent mudstones. This approach was combined with high‐resolution correlation of bioevents using graphic correlation. A detailed layering scheme for the Fleming field was defined and this predicted the presence of a field‐wide mudstone. Initial attempts at history matching during reservoir simulation using a simple six‐layer lithostratigraphical scheme were not successful. A revised layering scheme defined by biofacies modelling and graphic correlation was used to produce a 13‐layer model; this was later simplified by combination with the six‐layer model to produce a ten‐layer model. This layering scheme is shown to provide a better understanding of both net‐to‐gross distribution and the dynamic behaviour of the field, and also improved history matching against production data. The biostratigraphical model applied using a fuzzy logic approach is authenticated by the reservoir simulation (fluid flow) and pre‐ and post‐maintenance well pressure tests of well 22/5b‐A3 which showed that the perforated interval in that well is isolated from the perforated intervals in the other producing wells. While history matching during reservoir simulation is important, the predictive capability of the fuzzy logic model proved to be critical to our understanding of the field.     

Evaluation of miscible and immiscible CO2 injection in one of the Iranian oil fields

Carbon dioxide (CO₂) flooding is one of the most important methods for enhanced oil recovery (EOR) because it not only increases oil recovery efficiency but also causes a reduction of greenhouse gas emissions. It is a very complex system, involving phase behavior that could increase the recovery of oil by means of swelling, evaporation and decreasing viscosity of the oil. In this study, a reservoir modeling approach was used to evaluate immiscible and miscible CO₂ flooding in a fractured oil field. To reduce simulation time, we grouped fluid components into 10 pseudo-components. The 3-parameter, Peng–Robinson Equation of State (EOS) was used to match PVT experimental data by using the PVTi software. A one-dimensional slim-tube model was defined using ECLIPSE 300 software to determine the minimum miscibility pressure (MMP) for injection of CO₂. We used FloGrid software for making a reservoir static model and the reservoir model was calibrated using manual and assisted history matching methods. Then various scenarios of natural depletion, immiscible and miscible CO₂ injection have been simulated by ECLIPSE 300 software and then the simulation results of scenarios have been compared. Investigation of simulation results shows that the oil recovery factor in miscible CO₂ injection scenario is more than other methods.     

Using downhole temperature measurement to assist reservoir characterization and optimization

Without initial seismic or detailed geological information, reservoir characterization is difficult. Downhole temperature distribution in horizontal wells is an important source that helps to characterize the reservoir and understand the bottom-hole flow conditions. The temperature measurements are obtained from permanent monitoring systems such as downhole temperature gauges and fiber optic sensors. Additionally, production history and bottomhole pressures are usually readily available and are routinely used for history matching to improve the initial geological models. By combining the downhole temperature distribution and the production history, more reliable information can be extracted about the reservoir permeability distribution and bottomhole flow conditions in order to optimize the wellbore performance, particularly in horizontal wells.In this paper, a thermal model and a transient, 3D, multiphase flow reservoir model are used to calculate the wellbore temperature distribution in horizontal wells. By comparing the simulated temperature and the observed data, large-scale permeability trends in the reservoir are derived. These permeability trends are then incorporated as ‘secondary’ information in the geologic model building and history matching. The final outcome is a geologic model that has the constraints of both temperature and production history information.A synthetic case is presented to illustrate the procedure. The results show when using production history matching only without distributed temperature data along the wellbore, the water entry location in horizontal wells cannot be detected satisfactorily. By combining production history matching with downhole temperature distribution data in a wellbore, an improved geological model is developed that can match production history and locate water entries correctly. Based on the downhole flow conditions and the updated geological model, the well performance can be optimized by controlling the inflow rate distribution in a horizontal well.     

基于贝叶斯理论的四维地震与生产动态数据的油藏历史拟合新方法

针对油藏历史拟合现有方法效率低、准确度差和难以拟合地震数据的不足,研究改进了多次数据吸收的集合平滑（ES-MDA）算法,提出了一种基于四维地震数据和井口生产数据的油藏历史拟合新方法。该方法通过对四维地震数据的粗化与稀疏化处理,并基于岩石物理学模型,建立起油藏状态与地震波响应的数学模型,形成油藏流体—地震属性耦合模拟程序;最后通过对ES-MDA算法的适应性改进,将由四维地震监测获得的纵波波阻抗数据与井口生产数据结合,实现四维地震与井口生产数据的联合历史拟合。对某海相油藏的应用研究表明,基于四维地震数据的油藏历史拟合方法增加了油田生产全过程油藏流体状态约束条件,历史拟合后的地质模型质量得到明显改善。