Characterization and modelling of oil reservoirs and groundwater aquifers: application of Wavelet Transformations

We describe wavelet transformations (WTs) and their basic properties, and discuss their application to analysis of complex and noisy data. These transformations are a powerful tool for data and image analysis by (1) providing a flexible spatial- and/or time-scale window which narrows when one focusses on small-scale features and widens when one wishes to analyze large scale features, and (2) providing the capability for analyzing special characteristics of a set of data or images around specific points. We discuss application of WTs to developing a unified and highly efficient method for characterization and simulation of porous media problems, from pore to field scale. The method uses WTs for data mining and characterization, scale-up of the geological (fine-scale) model of porous media, and interpretation of their transient flow properties. The data that can be treated by WTs include the direct data, such as various well logs and the permeability distributions, and the indirect data, such as seismic signals, and other characteristics of porous media. Wavelet transformations denoise the data, uncover their special features, and discover the structure of their distribution. They also provide an efficient method for processing seismic data, which are typically in huge volumes. Wavelet transformations can also analyze time-dependent flow data, such as long-term production data for oil reservoirs, as well as time-dependent seismic data (i.e., repeated measurements over regular time intervals). Therefore, one has, for the first time, a unified approach to characterization and modelling of large-scale porous media and extraction of information from their flow properties, from pore to field scale. The computational cost of the method can be orders of magnitude less than those of the most efficient methods currently available. Received: 30 March 2000     

肥城矿区充水含水层地下水动态研究

分析了1963~2005年肥城矿区40多年的水位和水质数据,研究了该地区充水含水层地下水动态规律。结果表明:四灰含水层呈疏干趋势,水质表现为HCO3-、Cl-、K++Na+减少,SO42-、Ca2+增加;五灰与奥灰含水层水位呈波浪式升降,水质表现为Ca2+增加,其他离子变化不明显,二者动态特征基本一致;而引起此动态变化的主要因素为大气降水、地质构造等。结合其他水文地质资料,该动态研究可以用来估算地下水的侧向补给量及更新速率,判断发生的水化学作用及速度,推断含水层水力联系方式及程度等。     

Investigation of the pH effect of a typical host rock and buffer solution on CO2 sequestration in synthetic brines

Carbon dioxide sequestration in deep saline aquifers is a critical component of long-term storage options. It is suggested that the precipitation of mineral carbonates is mostly dependent on brine pH and is favoured above a basic pH of 9.0. However, brine pH will drop to acidic values once CO₂ is injected into the brine. Therefore, there is a need to raise brine pH and maintain it stable. Synthetic brines were used here instead of natural brines because of the difficulty in obtaining and storing natural brines. Therefore, experiments were conducted to prepare a series of synthetic brines and to compare their suitability to natural brines for carbon sequestration firstly. A typical host rock (Oriskany rock) and a buffer solution (NaCl/NaHCO₃) were selected to buffer brine pH. In a subsequent step, studies were conducted to correlate how brine samples respond in the presence of the host rock or the buffer solution at realistic reservoir temperatures (40 and 100 °C) and pressures (1160 and 1500 psi) for CO₂ storage. The results show that synthetic brines prepared can be used as analogues as natural brines for carbon sequestration studies in terms of chemical composition and pH response. Both XRD and SEM/EDS analyses confirmed the presence of mineral carbonates in the CO₂-rock-brine and the CO₂-buffer-brine experiments. However, the amount of carbonates precipitated from the CO₂-buffer-brine reactions is nearly 18 times larger than that formed from the CO₂-rock-brine experiments. ICP-MS studies also verified that there was only 4% reduction in Ca concentration in solution after the CO₂-rock-brine studies, while the concentrations of Ca and Sr decreased by 90% during the CO₂-buffer-brine experiments.     

上海地区的承压含水层降水设计方法

简要论述了上海地区的地下水对地下工程建设的主要不利影响。提出了承压含水层降水概念设计新方法,包括安全承压水位埋深的修正计算公式、承压含水层降水方案的选用原则等。归纳、总结了针对不同水文地质条件与降水工程特征的承压含水层降水设计计算方法。工程实例表明,合理、可行的降水方案能够保证承压含水层降水效果与有效控制降水引起的周边环境变形。     

Hydrochemical Processes and Environmental Isotopic Study of Groundwater in Kuwait

Abstract

The present paper studies the hydrochemical processes and the isotopic characteristics of the main aquifers, the Kuwait Group and Dammam aquifers in the State of Kuwait. The water chemical types are dominantly NaCl and Na₂SO₄ in the Kuwait Group aquifer and Na₂SO₄, CaSO₄, and NaCl in the Dammam Limestone aquifer. The groundwater of the Kuwait Group aquifer is supersaturated with respect to quartz and calcite, and near saturation with respect to aragonite, but under-saturated with respect to anhydrite, dolomite, gypsum, and halite. While the groundwater of the Dammam aquifer is strongly under-saturated with respect to anhydrite, halite, and gypsum and is supersaturated with respect to quartz, dolomite, aragonite, and calcite. The saturation indices of the calcite and dolomite are increased in the direction of flow from southwest toward north-northeast. Al-Rawdhatain and Umm Al-Aish groundwater samples lie near the meteoric water line. They represent the effect of recharge by rainfall during pluvial period. The brackish palaeo-groundwater of the Dammam aquifer has low values of δ¹⁸O (?4.5 per mil) and δD (?35 per mil), which reveal that these waters are related to the palaeo-water from the cool wet period in the eastern Arabia 11,000 to 60,000 years B.P. The investigated brackish groundwater samples showed that the deuterium excess values are much lower than that of the Mediterranean areas. This may suggest that the evaporation was a prevailing process before the infiltration to the aquifers.     

Forecasting the underground waters regime in the pitching aquifers in Huainan mining area

Huainan area is an important coal base of the east of China. In the early part of the 1980s, the study of the underground waters dynamic state in the area was gradually paid close attention to. This paper introduces the observation system of the groundwater dynamic state in the multilayered pitching aquifer, and expounds the hydrogeologic feature and the waterpower relations among aquifers. Furthermore, based on the analysis of the relations of the groundwater dynamic state to surface water, meteoric water and mining shaft outflow rate, this paper establishes main water filled aquifers of mining shaft (C3-1, C3-2, (C3-3 and O2). In the light of the actual situation of the greatly changing aquifer occurrence and steep dip angle, the “two-layer space curved surface seepage model“ and the calculating step are all suggested. Since 1991, the groundwater dynamic state of the next year has been predicted (numerical simulation) every year. Contracting with the measured data, we gain a relatively ideal effect.     

中国天然气战略储备的需求和对策

通过对世界上部分国家和地区天然气战略储备发展状况及天然气储备经验的分析，得出：①天然气地下储备优于地表储备；②直接将天然气储存于地下的成本低于以液化天然气形式的储备；③枯竭油气藏地下储气最优，含水层地下储气次之。我国2020年前天然气战略储备的需求将达到250×108m3的工作气量，面对如此巨大需求，选择合适的库址和库型是非常重要的，结合我国油气资源远离天然气消费大城市和主要富集在非均质性较强的陆相地层中的特点，提出我国未来天然气地下战略储备应以海相含水层作为主要储集空间、并考虑其它多种库型的对策，并就不同投资主体在不同类型地下储气库建设中应发挥的作用提出了建议。     

水下采煤覆岩裂隙扩展判断方法及其应用

工作面突水是影响水体下煤层安全开采的主要隐患,而上覆岩层导水裂缝带发育是引起工作面突水的基本路径。基于裂隙萌生发育的形态分析,将导水裂隙带划分为两种类型,一是原生裂隙的张开或滑动,二是新生裂隙向完整结构的扩展;而且,在工程荷载作用下卸荷裂隙的萌生和扩展具有优势定向性特征。考虑开采煤层覆岩裂隙的分布特征,基于格里菲斯摩尔-库伦准则建立了裂隙扩展的分析模型和判断方法。借助FISH语言,将扩展模型耦合入离散元软件UDEC中,并用其模拟水体下煤层开采过程,分析在工作面推进过程中上覆岩层内裂隙带萌生演化特征。分析了工作面突涌水机理,得出了水下采煤工作面覆岩导水裂隙带高度的确定方法。并结合导水裂隙带高度现场观测实践进行了工程验证。     

Hydrogen storage in saline aquifers: The role of cushion gas for injection and production

Hydrogen stored on a large scale in porous rocks helps alleviate the main drawbacks of intermittent renewable energy generation and will play a significant role as a fuel substitute to limit global warming. This study discusses the injection, storage and production of hydrogen in an open saline aquifer anticline using industry standard reservoir engineering software, and investigates the role of cushion gas, one of the main cost uncertainties of hydrogen storage in porous media.The results show that one well can inject and reproduce enough hydrogen in a saline aquifer anticline to cover 25% of the annual hydrogen energy required to decarbonise the domestic heating of East Anglia (UK). Cushion gas plays an important role and its injection in saline aquifers is dominated by brine displacement and accompanied by high pressures. The required ratio of cushion gas to working gas depends strongly on geological parameters including reservoir depth, the shape of the trap, and reservoir permeability, which are investigated in this study. Generally, deeper reservoirs with high permeability are favoured. The study shows that the volume of cushion gas directly determines the working gas injection and production performance. It is concluded that a thorough investigation into the cushion gas requirement, taking into account cushion gas costs as well as the cost-benefit of cushion gas in place, should be an integral part of a hydrogen storage development plan in saline aquifers.     

Strategy for solving semi-analytically three-dimensional transient flow in a coupled <Emphasis Type="Italic">N</Emphasis>-layer aquifer system

Efficient strategies for solving semi-analytically the transient groundwater head in a coupled N-layer aquifer system , i = 1, ... , N, with radial symmetry, with full z-dependency, and partially penetrating wells are presented. Aquitards are treated as aquifers with their own horizontal and vertical permeabilities. Since the vertical direction is fully taken into account, there is no need to pose the Dupuit assumption, i.e., that the flow is mainly horizontal. To solve this problem, integral transforms will be employed: the Laplace transform for the t-variable (with transform parameter p), the Hankel transform for the r-variable (with transform parameter α) and a particular form of a generalized Fourier transform for the vertical direction z with an infinite set of eigenvalues (with the discrete index m). It is possible to solve this problem in the form of a semi-analytical solution in the sense that an analytical expression in terms of the variables r and z, transform parameter p, and eigenvalues of the generalized Fourier transform can be given or in terms of the variables z and t, transform parameter α, and eigenvalues . The calculation of the eigenvalues and the inversion of these transformed solutions can only be done numerically. In this context the application of the generalized Fourier transform is novel. By means of this generalized Fourier transform, transient problems with horizontal symmetries other than radial can be treated as well. The notion of analytical solution versus numerical solution is discussed and a classification of analytical solutions is proposed in seven classes. The expressions found in this paper belong to Class 6, meaning that the transformed solutions are written in terms of eigenvalues which depend on one transform parameter (here p or α). Earlier solutions to the transient problem belong to Class 7, where the eigenvalues depend on two transform parameters. The theory is applied to three examples.