Excessive emission of greenhouse gases into the atmosphere has resulted in a progressive climate change and global warming in the past decades. There have been many approaches developed to reduce the emission of Carbon Dioxide (CO₂) into the atmosphere, among which Carbon Capture and Storage (CCS) techniques has been recognized as the most promising method. This paper provides a deeper insight about the CCS technology where CO₂ is captured and stored in deep geological formations for stabilization of the earth's temperature. Principles of capturing and storage for a long-term sequestration are also discussed together with the processes, mechanisms and interactions induced by supercritical CO₂ upon injection into subsurface geological sites.

The diagenetic evolution of the moldic-pore-containing gypsum dolomites of the Middle Ordovician Majiagou Formation in the eastern Ordos Basin, central China, was studied by means of petrological, mineralogical, and geochemical analyses, to improve our understanding of heterogeneity in high-quality reservoirs. The aim of the study was to elucidate the processes that resulted in reservoir tightness and the formation of sweet spots, to guide future exploration. Results show that the moldic-pore-containing gypsum dolomites are the most favorable reservoir in the study area, with a mean porosity of 4.96% and a mean permeability of 0.748 mD. The development and preservation of gypsum moldic pores were the main factors causing reservoir heterogeneity. Specifically, moldic pore development was controlled by the sedimentary microfacies, whereas pore preservation was related to dissolution and filling during telogenetic diagenesis. There were three main dissolution-filling stages that took place in three settings: penecontemporaneous, epigenetic, and burial. These processes controlled the formation of reservoir sweet spots. Early-consolidated dolomite deposits were frequently exposed to the atmosphere in the penecontemporaneous environment under the influence of high-frequency sedimentary cycles, which led to the dissolution of evaporite minerals and consequent formation of gypsum moldic pores, accompanied by infilling by freshwater calcite. During epigenesis, the porosity initially increased due to karstification, then significantly decreased because of calcite infilling resulting from long subaerial exposure (120 Myr), which contributed to reservoir heterogeneity. Finally, during burial the high-temperature and high-pressure conditions led to chemical compaction and continuous tightening of the reservoir, although some burial dissolution also took place. In conclusion, the variable paleo-topography resulted in differences in the intensity of pore filling among the blocks in the study area, resulting in reservoir heterogeneity.

Reservoir model history matching is a multiobjective optimization problem. It involves the adjustment of relevant reservoir model input parameters, to minimize the mismatch between simulated and observed reservoir responses and to obtain a diverse set of geologically plausible reservoir simulation models. Typically, single objective optimization methods are adopted during history matching. This requires weighted sum scalarization. However, scalarization biases the optimization search, limiting the diversity of the recovered solutions. In this work, a computer assisted history matching procedure based on transform parameterization and a multiobjective evolutionary algorithm with dominance and decomposition (MOEA/DD) is proposed. In the procedure, history matching is treated as a multiobjective optimization problem, parameterized in terms of a small number of kernel principal component analysis (KPCA) variables. KPCA provides efficient parameterization of the reservoir model input property fields. Concurrently, MOEA/DD provides robust and unbiased optimization over multiple objectives. The effectiveness of the proposed procedure is demonstrated with the UNISIM-I-H history matching benchmark problem.

In recent years, controlling the salinity and composition of the injected water has become an emerging enhanced oil recovery (EOR) technique, often described as low salinity (LS) waterflooding. This work is done with the intention to contribute to the ongoing discussions about LS waterflooding mechanism(s). For this purpose, a series of different experiments were conducted. At first, the effect of salinity on the interfacial tension (IFT) and the contact angle was evaluated with a crude oil sample. Then to achieve more accurate results in observing oil/water interface, similar IFT experiments were also carried out on a synthetic oil containing asphaltenes. Thereafter, microscopic visualization using glass micromodel was performed on the interface of the synthetic oil sample and brines. Four brine solutions including Sea Water (SW), it's dilutions and formation water (FW) were used for various experiments. Finally, to investigate the presented mechanism by other Authors, a series of Environmental Scanning Electron Microscopy (ESEM) analysis on the synthetic oil was carried out to understand better the phase behaviour after contacting both synthetic oil and water phases from the micromodel experiment. Based on the existing mechanism, there exists an optimal concentration beyond which dilution is no longer an effective process.

The present research is to experimentally study the joint effects of external pressure and vibratory excitations of low frequency on oil slug mobilization and flow in a capillary model. During and after the oil slug mobilization, the flow phenomena and pressure drop variation across the model are investigated. The distance travelled by the oil slug subjected to various external pressure and vibratory excitations are also studied. The experimental results obtained indicate that the external vibratory excitation acting on the model has positive effect on the flow and mobilization of the oil slug in the model. It is found in the research, with the application of the excitation, the contact angle between the oil slug and tube-wall is changed; the maximum pressure required to mobilize the oil slug is reduced accordingly; and the oil slug travel distance is increased in comparing with that without external excitations. This research contributes to the comprehension of improved liquid mobilization in porous media under the application of external excitations. The finding of the research is significant for studying the two-phase liquid flow in porous media subjected to external excitations and provides insights for Enhanced Oil Recovery with waterflooding and vibratory stimulations.

The permeability of the rock is usually measured by the injection of gas using Darcy's flow model (pulse-decay). For oil formations, helium and nitrogen are the most common gases used to measure the permeability of the rock. However, recent approaches are based on the use of methane as it minimizes the properties difference between the testing fluid and reservoir fluid. This work focused on the latter approach to compute the correction of gas adsorption. The most widely used model is Cui et al. model that is based on Langmuir adsorption isotherm. In this work, we introduced a modified model that is based on Freundlich isotherm. This model also includes the correction for gas adsorption such as Freundlich isotherms proved to be more appropriate for the adsorption on intact reservoir rock. The model is based on gas and rock properties and reduced pressure and temperature were used to accommodate the gas compressibility. The modified model can also capture effective porosity of adsorption (ϕa) that can correct the pulse-decay storage capacity parameters a and b. The permeability estimation of ultra-tight samples using the modified approach is enhanced owing to the correction in the storage volume and rock porosity. Including the proper adsorption isotherm enhanced the porosity estimation because Langmuir isotherm yielded 11% porosity and Freundlich isotherm yielded 12% porosity. Similar results were obtained in the permeability estimation, Langmuir isotherm resulted in a 1.5% error compared to zero error in the Freundlich isotherm estimation.

Guar gum and its derivatives have been the most commonly used polymers to increase the viscosity of fracture fluids. Ceramic proppants are vital products for enhancing oil and gas well productivity in low-permeability reservoirs. In the last several decades, abundant studies have been found in the investigation of proppant size, shape, compositions on the fracture conductivity. However, few types of research can be found to study the proppant wettability effect on the oil and gas flow efficiency. In our research, eight experiments were conducted using traditional guar gum fracturing fluid. Results of this work indicated that ceramic proppant promotes oil flow efficiency from sandstone core samples to proppant packs and thus should promote oil well productivity. The mechanism behind this phenomenon is believed to be the formation of oil flow channels across the fracture face due to the imbibition of oil in the core onto the oil-wet surface of the proppant, promoting oil flow from the core to the fracture. After guar gum was added the results inverted, this phenomenon for water-wet proppant is believed to be increased by the viscosity of fracture fluids which increased the viscosity of water, promoting oil flow from the core to the fracture. Nevertheless, the stimulation effect of oil-wet proppant on oil flow efficiency can be reduced by the presence of guar gum solution. Inside the proppant matrix filled with guar gum fracturing fluid, oil can be blocked inside the proppant matrix as a discontinuous phase while the aqueous phase can be easily mixed with the guar gum fluid and then be transferred out.

During cementing operations involving cement slurry contamination, problems often occur due to the inaccurate calculation of the space fluid volume. This study, based on the turbulent dispersion theory, developed a minimum volume calculation model of spacer fluid to prevent cement slurry contamination. This model was used to analyze influence factors and practical calculations. The results indicated that the minimum volume of spacer fluid increase with the eccentricity of casing and injection rate and decrease with the density of cement slurry. Additionally, the better rheological properties of the cement slurry and spacer fluid would increase the volume of the spacer fluid. Furthermore, this model fitted actual field data better than other heat calculation models.

Compounding polymer AP-P4 with high viscosity-reducing Gemini Surfactant HD, which is used as an emulsifier viscosity reduce, to improve the stability of the O/W emulsion while the viscosity reduction rate is kept. A polymeric surfactant emulsification and viscosity reduction system capable of forming a relatively stable O/W emulsion of heavy oil (0.5% HD+0.1% AP-P4) is then compounded. The system has been characterized as a high viscosity reduction rate and high stability. Meanwhile, the production liquid does not need to be added with a demulsifier and only needs to be heated to 70 °C to achieve effective demulsification. The influencing factors of the performance of the polymetric surfactant emulsification and viscosity reduction system were studied. When the oil-water ratio was 70:30 and 60:40, the viscosity reduction rate was 97.47% and 99.09%, respectively; after 15 h at 30 °C, the dehydration rates were 95.8% and 99.2%, respectively. The dehydration rate after 15 h at 70 °C was 98.1% and 99.4%, respectively; at 30 ~ 50 °C, the water phase temperature has a greater impact on the viscosity; at 60 °C, 70 °C, the water phase temperature has little effect on the viscosity; as the temperature of the aqueous phase increased, the stability of the emulsion deteriorated. When the aqueous phase temperature was 30 °C, 50 °C and 70 °C, the dehydration rates of the emulsion after 15 h were 95.8%, 96.7% and 98.1%, respectively; As the degree of mineralization increases, the viscosity reduction rate decreases, and the stability of the emulsion deteriorates. The system has been used in field test for 2 injection wells, and the production rate of the two wells increased with a peak value of 25 m³/d and 20 t/d, respectively.

The expansibility and mechanical properties of shale are significantly influenced by water-based muds (WBMs); thus, it is necessary to mitigate this effect to avoid borehole instabilities in drilling operation. Potassium chloride (KCl) is usually used as inhibitor to reduce hydration of shales. In this study, we investigated the inhibitory efficiency of KCl on shale through a series of experiments, including dynamic linear swelling (DLS) tests and uniaxial compressive strength (UCS) tests, to provide reference for the design of WBMs. These tests were conducted on shale samples soaked in KCl solution for 24, 48, 72, and 96 h with saline concentrations of 0%, 2%, 4%, 6%, and 8%. Experimental results show that samples with microcracks and bedding fissures have the highest swelling increase and the largest strength reduction after immersion in solution. The swelling potential decreased with increasing KCl concentration. In addition, KCl exhibited a certain inhibitory effect on the weakening of the mechanical properties of samples. An increase in the KCl concentration increases the compressive strength and elastic modulus, and decreases the Poisson's ratio. However, in terms of homogeneous samples, the UCS test results show that exposure to water is weakly related to weakening of the mechanical properties of shale samples. We found that immersing the shale in KCl solution for a longer time decreases the compressive strength, increases the Poisson's ratio, and decreases the elastic modulus.

An experimental study was conducted to investigate the effects of four different additives on pour point and cloud point temperatures of a diesel fuel. Sample mixtures were prepared in different volumetric percentages of four different additives (Ethanol, Toluene, n-Heptane and Xylene) and diesel fuel mixture. Pour point and cloud point temperatures of the blends were measured using standard ASTM D2500 and ASTM D97-96a methods, respectively. Introducing the additives to the diesel fuel did not lead to a significant reduction in cloud point temperature of the fuel. In fact, the greatest obtained reduction in cloud point temperature was achieved using 20 vol% or more of Toluene-diesel fuel mixtures. Although cloud points did not change significantly, even the slightest amounts of additives caused a high reduction in the pour point temperature of the fuel. Ethanol was the most effective additive in lowering the pour point temperature of the fuel. A 20% ethanol-fuel mixture caused nearly a 30° reduction in the fuel pour point temperature. Therefore, knowing that none of the additives has a significant effect on cloud point temperature, while the greatest reduction in pour point temperature is achieved using ethanol even in low Vol%s, it can be concluded that the most efficient additive among these four additives to alter cold flow properties of a certain diesel fuel is Ethanol.

When a pig mounted with permanent magnets gets stuck in the pipeline, it can be located by detecting the magnetic anomalies on the ground using a single-axis magnetic sensor. In order to collect the magnetic anomaly efficiently through single-axis magnetic sensor, a geometric detection model and calculation method for single-axis magnetic anomaly detection is established in this paper. The distribution of magnetic inclination and declination of the measuring points is obtained. The results indicate that the magnetic inclination of all measuring points vary within a small range of 2°, and this value is highly dependent on the magnetic sensor which is configured aboveground around the geomagnetic inclination. However, the magnetic declination at different points of detection surface is subject to the geomagnetic components and the Y-axis component of the magnetic field of magnets. The magnetic declinations distribute irregularly and vary in a wide range. Therefore, to achieve a high-efficiency detection with the single-axis sensor, the sensor shall be placed in such a manner that the magnetic inclination thereof coincides with the geomagnetic inclination. The magnetic declination of the sensor can be calculated using s, the superposed Y-axis component induced by the permanent magnets, and the corresponding formula given in this paper. The article demonstrates the feasibility of locating a blocked pig in the pipeline based on the single-axis magnetic anomaly detection. It will have a practical significance in guiding the engineering detection.