查看更多>>摘要：Some subtle reservoirs are hidden in the weak reflection areas and thin layers in seismic profiles, and they cannot be identified easily. Thus, the thin layer interpretation and the subtle reservoir prediction are the essential in reservoir management plan while field development and production stage. To improve the recognition capability in the weak reflection areas and resolution, the fixed-point (FP) algorithm is employed to obtain the inversion results since the conventional FP seismic inversion (CFPSI) is sensitive to the weak changes in seismic signals. However, the CFPSI suffers from low convergence. Therefore, the new iterative equations of pre- and post-stack FP seismic inversion are designed to improve the computational efficiency and convergence. Besides, a new constraint, which is derived from the instantaneous phase of the seismic trace, is also sensitive to the weak changes of the seismic signal. The instantaneous phase constraint is then involved in the objective function, contributing to a significant improvement of identification capability in weak reflection areas and the resolution of inversion. Additionally, the initial model constraint is introduced into the objective function to weaken the multi-solution and noise sensitivity. The synthetic examples demonstrate that the computational efficiency, recognition capability in the weak reflection areas and resolution of the proposed approach are higher than those of the CFPSI. The field examples suggest that the subtie reservoirs and thin layers, which are hidden in the weak reflection areas in the field data, are accurately identified using our method. Thus, the proposed method is useful for improving the recognition capability in weak reflection areas and resolution of the inversion results.
查看更多>>摘要：Pressure prediction has long been one of subject of research focuses in petroleum geology and exploration, but is traditionally limited to moderately overpressured formations due to disequilibrium compaction based on the empirical velocity-pressure model. Overpressures in the Xihu depression are caused by fluid expansion due to the generation of natural gas in source rocks. The resulting abnormally pressured gas reservoirs manifest as a high-pressure structure with the thick mud-coated thin sand (MCS) that remains largely unaddressed in prediction. Such gas-producing overpressures make traditional prediction methods unapplicable because of the significant influence of high gas contents on seismic velocities. We employ a frequency-dependent quality factor Q-pressure petrophysical model because of the sensitivity of acoustic attenuation to overpressures. However, acoustic attenuations from rock physics and sonic logging present an uncertain dependence on pore pressures. This implies that overpressure prediction is a typical physical system that is characterized by both deterministic mechanism and statistical behavior, which resorts to physics-informed deep learning methods. We take the Q-pressure petrophysical model as the activation function of Caianiello convolutional neurons with an attempt to combine deterministic and statistical mechanisms for overpressure prediction. Such convolutional neurons render strong feature extraction and powerful learning ability and are used to construct physics-informed Caianiello convolutional neural networks (CCNNs) for overpressure prediction in the Xihu depression. The comprehensive CCNNs-based seismic inversion scheme for overpressures consists of reservoir petrophysical modeling, deep learning for neural wavelets, well-seismic correlation analysis, deconvolution-based inversion for an initial pressure model, and input-signal reconstruction to improve the initial pressure model. With drill stem tests (DSTs), well logs, and 3D seismic data, we conduct the overpressure prediction associated with cross validation in the Xihu depression, which demonstrates the applicability of the physics-informed CCNNs inversion scheme. Predicting reliability away from the training wells usually depends on the geological complexity of areas under study. Nevertheless, the information representation in the trained CCNNs can be improved gradually by feeding new well data during the development of an oil field.
查看更多>>摘要：The high efficiency of Low Salinity Water (LSW) injection in carbonates, leading to rock wettability alteration from oil-wet to water-wet and, hence, resulting in better oil displacement, has been confirmed by numerous studies. In recent years, the combination of LSW injection with other Enhanced Oil Recovery (EOR) techniques has been widely discussed, to activate the synergistic effects of hybrid EOR methods leading to additional oil recovery. The idea of combining LSW injection with a thermal approach, known as Low Salinity Hot Water (LSHW) injection, is a highly promising hybrid EOR method for heavy oil carbonate formations. In this study, the performance of LSW and hybrid LSHW injection was experimentally evaluated for heavy oil carbonate cores by different measurements of rock-fluid interactions and core flooding experiments. Contact angle measurements were conducted to investigate the optimal dilution of seawater (SW) and evaluate the performance of different variations of Potential Determining Ions (PDIs) concentration on wettability change. Appropriate dilution and ion management was applied to design LSW and engineered water (EW) for oil displacement at different temperatures (from 20 to 70 °C) in order to evaluate the standalone LSW and hybrid LSHW injection performance. The injection of LSW and EW was estimated to be inefficient for heavy oil carbonates, while hybrid LSHW flooding showed a significant increase of oil recovery with the best performance of the brine spiked by PDIs, where 60% and 55% of the residual oil was displaced at 50 °C and 70 °C, respectively. Moreover, the injection of LSHW directly after SW was found to be more practical than following LSW flooding. The application of the hybrid EOR method activates different mechanisms, such as oil detachment from the rock surface, due to the wettability alteration by EW/LSW and viscosity reduction by the thermal methods. Combined active mechanisms result in better performance, compared to the standalone EOR methods. Rock dissolution and multi-ion exchange by PDIs were identified as the main mechanisms of wettability alteration by EW/LSW via the results of ion chromatography analyses. The synergy between EOR methods affects the active mechanisms of LSW/EW flooding. For example, an increase in temperature showed more active multi-ion exchange and rock dissolution, which resulted in higher oil release from the rock surface.
查看更多>>摘要：The objectives of this study are to characterize the properties of water-SiO2 nanofluid and quantify its flooding efficiency in an initially oil-filled micro-porous medium of two different surface wettability conditions, i.e. water, wet and neutral-wet. The average nanoparticle size (as a result of aggregation) in water-SiO2 nanofluid is characterized using dynamic light scattering method. Viscosity and surface tension of water-SiO2 nanofluid are measured respectively by vibration string and drop volume methods. For the flooding experiments, a transparent PDMS microcharmel with internal square obstacles mimicking a porous medium is designed and fabricated. The wettability of PDMS over time, as a result of aging, is investigated. The effect of SiO2 nanoparticles on 3-phases contact angle (nanofluid, crude oil and PDMS) is reported. The flooding efficiency of water-SiO2 nanofluid is then quantified. The results reveal that the best oil recovery process occur when the water-SiO2 nanofluid flooding is used in a neutral-wet surface condition. As the injection rate increases, the oil displacement efficiency decreases. This oil recovery behavior implies the dominant nature of viscous forces at low flow rate. At high flow rate, the effect of viscous force is not obvious.
查看更多>>摘要：This work focuses on a typical low-permeability carbonate reservoir in Middle East that has been developed by miscible hydrocarbon (HC) gas flooding for more than 10 years. The oilfield is now suffering from gas channeling, high gas/oil ratio (GOR), and invalid gas circulation. To figure out the reasons and propose an optimized development plan, it is necessary to accurately determine the characteristics and behavior of miscible gas flooding. To achieve this, a comprehensive performance evaluation method for miscible gas flooding is established in this work by integrating production data, inter-well gas tracer test, saturation surveillance, pressure surveillance, minimum miscibility pressure (MMP) variation, and streamline simulation. The following miscible HC gas flooding characteristics are interpreted, including typical gas flow path, miscibility behavior, major controlling factors impacting performance, and the main challenges of the current development scheme, which provides a fundament for proposing mitigation plan. By using this evaluation method, the behavior of gas flow in the ongoing miscible flooding process is precisely characterized, which is a 'gravity override-gas coning' mode in which gas override is formed by an upward injected gas flow and then gas flows through gas cap to producers that leads to gas coning, resulting in high GOR and invalid gas circulation. This flow mode mainly resulted from the unsatisfied miscibility that led to gas escaping from miscible phase and gas channeling. Furthermore, it was found out that pressure difference is the dominating factor for gas channeling. In addition, we also found that MMP varies during HC gas injection process due to the change in the oil composition, which emphasizes the importance of recovering and maintaining pressure. Based on these findings obtained from extensive dynamic performance analysis and numerical simulations, an optimization strategy is finally proposed for improving the performance of miscible HC gas flooding.
查看更多>>摘要：Molecular diffusion of acid into a porous carbonate medium is usually referred to as acid imbibition. Accurate prediction of acid penetration into a formation and reaction with rock is not possible without a comprehensive understanding of the acid diffusion process and associated parameters. This work aimed to derive an analytical solution for mineral-dissolution reactive diffusion when acid imbibes into a rock surface and where there is no flow condition under laboratory conditions. For the experimental part of the study, different disk samples of Eagle Ford shale were selected, and the effect of acid diffusion on the rock surface was fully investigated. Digital microscopic images confirm that with differing concentrations of consumed acid and saturation front movement, varying degrees of reactivity are conceivable, including surface reaction, surface dissolution, matrix acidizing, and induced fracturing. For the mathematical modeling section, a continuity equation without an advection term and only a diffusion term was considered. An analytical solution was found for the dissolution of minerals as a result of reactive imbibition in a porous medium with porosity variations. The final form of the equation and the analytical solution is proposed here for the first time. Additional experiments were performed on Indiana limestone samples as control tests, with all experimental results matching perfectly with the developed analytical solution. Data from the literature relating to different temperatures also matched appropriately with the mathematical solution, effectively affirming the validity of the suggested solution. The proposed approach can be used as a predictive tool to verify the reactive models leading to porosity creation in the field scale.
查看更多>>摘要：In situ stress is one of the key engineering parameters that ensures caprock integrity in steam-assisted gravity drainage (SAGD) operations. Massive steam injections during an SAGD operation leads to significant changes in the pore pressure, temperature, stress, and volumetric strain in the rock formations. These changes trigger deformation and stress redistribution in the overburdened strata, which could lead to a containment breach of the caprock through shear or tensile failure. To ensure subsurface steam containment, both to satisfy public safety considerations and instill confidence that the steam containment will continue over the necessary time-scales, the Alberta government requires every SAGD operator to measure the in situ stress conditions in the oil sands reservoir and its caprock. Minifrac test is a suggested method that can measure the minimum principal stress with high confidence. A safety factor (SF) of 80% is used to determine the maximum operation pressure (MOP) for safe SAGD operations; in other words, MOP = 80%~*σ_(min), where σ_(min) is the minimum principal stress at the base of the caprock. In most cases, this 80% SF safeguards the SAGD injection pressure to always remain lower than the σ_(min) at the base of the caprock, ensuring that no tensile fractures are initiated at the caprock. In this study, we compiled a database containing in excess of 100 minifrac datasets across the Athabasca oil sands region and constructed an in situ stress map. Based on our in situ stress dataset, we developed a quantitative risk model to analyze the effects of uncertainties on the probability of exceedance (i.e., the probability that the MOP exceeds the fracture pressure at the base of the caprock). The risk model involves denning probability distributions to quantify the uncertainties at the shallowest depth and minimum stress gradient. The output of the risk model was a set of predictions of exceedance probabilities, which were computed using Monte Carlo simulations. Through a statistical analysis of this in situ database and risk-based simulation analysis, this study demonstrates the reliability of a SF of 80%.
查看更多>>摘要：Accurate three-dimensional modeling has an important influence on the evaluation and prediction of the physical properties of porous media. In view of the inherent natural structures, pores are multiscale in many porous media. As a result of the tradeoff between the field of view (FOV) and resolution, it is difficult to obtain high-resolution and large-scale images using single-resolution imaging equipment. Generally, low-resolution images with a large FOV lack detailed features, while the FOV of high-resolution images is too small to contain the information of the entire microstructure. Therefore, fusing images from different resolutions and scales to reconstruct models is an promising solution for addressing these issues. In this study, an improved method for reconstructing a high-resolution and large-scale model based on three-dimensional pattern matching in proposed. The algorithm can fuse two models from different resolutions and scales, in which the structures of large-scale pores in the low-resolution model are used as background and a high-resolution model is applied to build pattern sets to reconstruct fine-scale pores based on the background. The final result is a model containing large-scale and fine-scale pores. The accuracy and stability of the proposed method were tested by using two samples. From subjective and objective perspectives, through the comparisons of visual effects and statistical properties between generating models and target models, we found that the method can reconstruct accurate models.
查看更多>>摘要：3D models of the 300 t/d Gas Full Circulation Retort are developed to investigate the flow behavior of oil shale particles in the retorting process using the discrete element method (DEM). The results show that the flow patterns of oil shale particles gradually change from horizontal to waved along the radius direction in the descending process due to the friction between particles and walls. The cumulative contact energies are mainly concentrated at the top of the center pillar and the bottom half of the three support structures. With the addition of the conical structure for gas-oil mixture gathering and the triangular structures for particle distribution, the oil shale particles distribute more uniformly in the retorting zones. The interaction force among particles decreases obviously under those added structures, which is conducive to the enhancing of the convective heat transfer between gas heat carrier and particles. And the cumulative contact energies on the center pillar and three support structures decrease obviously, which could decrease the abrasion of refractory brick structures of the retort.
查看更多>>摘要：In this work, the freezing process has been expedited with elevating the concentration of nanoparticles and increasing their shape factor. The driving force of solidification is conduction mode and it is reasonable proposition to neglect the buoyancy force in deriving the mathematical model. Due to absence of velocity term, only temperature equation with involve of unsteady source term of phase changing have been involved. For better visual presentation of speed of freezing, solid front has been portrayed for various cases. The impacts of shape factor and volume concentration of copper oxide have been demonstrated in outputs. The patterns of grid demonstrate the adaptive grid and the code were verified according to previous publication. With growth of concentration of CuO, the period declines around 11.72% which is associated with elevation of conductivity. Moreover, outputs revealed that with imposing higher shape factor, the process finished in lower time about 5.96%.
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