Parallel numerical simulation for a super large-scale compositional reservoir

 A compositional reservoir simulation model with ten-million grids is successfully computed using parallel processing techniques. The load balance optimization principle for parallel calculation is developed, which improves the calculation speed and accuracy, and provides a reliable basis for the design of reservoir development plan. Taking M reservoir as an example, the parallel numerical simulation study of compositional model with ten million grids is carried out. When the number of computational nodes increases, message passing processes and data exchange take much time, the proportion time of solving equation is reduced. When the CPU number increases, the creation of Jacobian matrix process has the higher acceleration ratio, and the acceleration ratio of I/O process become lower. Therefore, the I/O process is the key to improve the acceleration ratio. Finally, we study the use of GPU and CPU parallel acceleration technology to increase the calculation speed. The results show that the technology is 2.4 ∼ 5.4 times faster than CPU parallel technology. The more grids there are, the better GPU acceleration effect it has. The technology of parallel numerical simulation for compositional model with ten-million grids presented in this paper has provided the foundation for fine simulation of complex reservoirs.Cited as: Lian, P., Ji, B., Duan, T., Zhao, H., Shang, X. Parallel numerical simulation for a super large-scale compositional reservoir. Advances in Geo-Energy Research, 2019, 3(4): 381-386, doi: 10.26804/ager.2019.04.0

Injection parameters optimization of crosslinked polymer flooding by genetic algorithm

The crosslinked polymer flooding, which is developed on the basis of polymer flooding, is a new type of flooding technology. As an EOR method, cross-linked polymer flooding has become a research hotspot. In the process of cross-linked polymer flooding, if the concentrations of the polymer and the crosslinking agent are small, the viscosity of the solution is low, and it will not achieve the oil displacement effect. Meanwhile, if the concentrations of the polymer and crosslinking agent are large, the viscosity of the solution is high, it needs high pressure to drive it flowing in the formation. Further, with the increasing injection of chemical agents, the contradiction between reduced production and increased cost has presented. The performance of crosslinked polymer flooding depends on the interaction of these two factors. Therefore, the concentrations of polymer and crosslinking agent should be optimized. In this paper, an optimal design method is proposed by using genetic algorithm with global optimization characteristics algorithm, combining with the chemical flooding numerical simulation software UTCHEM, the concentrations of the chemical agents are optimized. Firstly, the cumulative oil production is calculated by numerical simulation software UTCHEM, then the concentrations of the chemical agents are randomly generated by the genetic algorithm in the encoding process, and the fitness function takes the profit of cross-linked polymer flooding. Given a set of initial values, through crossover and mutation of population, optimized injection concentrations of the polymer and cross-linking agent are obtained by the multi-generational calculation.Cited as: Lian, P., Li, L., Duan, T. Injection parameters optimization of crosslinked polymer flooding by genetic algorithm. Advances in Geo-Energy Research, 2018, 2(4): 441-449, doi: 10.26804/ager.2018.04.0

Characteristics of gas-oil contact and mobilization limit during gas-assisted gravity drainage process

Gravity can reduce the instability of the gas-oil contact that is caused by gas channeling in locations with low flow resistance, such as high-permeability layers, macropores, and fractures during the gas-assisted gravity drainage process. Herein, the microscopic forces during the gas-assisted gravity drainage process were analyzed and combined with the capillary model to study the occurrence boundary of gas-assisted gravity drainage process, and the characteristics of the gas-oil contact in the gas-assisted gravity drainage process was discussed. The results show that free gravity drainage occurs only in pores where a certain height of the oil column and pore radius are reached. Furthermore, the lower the oil-gas interface migration rate, the easier free gravity drainage occurs. In other scenarios, additional gas injection is required. During the gas-assisted gravity drainage process, the gas-oil contact moves down stably as a transition. The width of the transition zone and the available pore radius are related to the gas-oil contact migration rate and the oil viscosity; the smaller the gas-oil contact migration rate and the lower the oil viscosity, the smaller pore throat can be involved in mobilization. Optimizing the gas injection rate and reducing the oil viscosity can delay the gas channeling maturity time, which is beneficial for the realization of the gas-assisted gravity drainage process. Finally, a method considering micropore heterogeneity is established for determining the critical gas injection rate, while the mainstream pore throat can be involved in mobilization and the gas-oil contact can be stabilized at the same time. The method of determining the critical gas injection rate can help researchers and reservoir engineers to better understand and implement the gas-assisted gravity drainage process.Cited as: Kong, D., Gao, J., Lian, P., Zheng, R, Zhu, W., Xu, Y. Characteristics of gas-oil contact and mobilization limit during gas-assisted gravity drainage process. Advances in Geo-Energy Research, 2022, 6(2): 169-176. https://doi.org/10.46690/ager.2022.02.0

Genome-wide Association Study (GWAS) of mesocotyl elongation based on re-sequencing approach in rice

Annotation of candidate genes anchored by associated SNPs. (XLSX 34 kb

A Review of Converter Circuits for Ambient Micro Energy Harvesting

The Internet of Things (IoT) has a great number of sensor nodes distributed in different environments, and the traditional approach uses batteries to power these nodes: however, the resultant huge cost of battery replacement means that the battery-powered approach is not the optimal solution. Micro energy harvesting offers the possibility of self-powered sensor nodes. This paper provides an overview of energy harvesting technology, and describes the methods for extracting energy from various sources, including photovoltaic, thermoelectric, piezoelectric, and RF; in addition, the characteristics of the four types of energy sources and the applicable circuit structures are summarized. This paper gives the pros and cons of the circuits, and future directions. The design challenges are the efficiency and size of the circuit. MPPT, as an important method of improving the system efficiency, is also highlighted and compared

Numerical Simulation Modeling of Carbonate Reservoir Based on Rock Type

There are many types of carbonate reservoir rock spaces with complex shapes, and their primary pore structure changes dramatically. In order to describe the heterogeneity of K carbonate reservoir, equations of porosity, permeability, and pore throat radii under different mercury injection saturations are fitted, and it shows that 30% is the best percentile. R30 method is presented for rock typing, and six rock types are divided according to R30 value of plugs. The porosity-permeability relationship is established for each rock type, and the relevant flow characteristics of each rock type have been studied. Logs are utilized to predict rock types of noncored wells, and a three-dimensional (3D) rock type model has been established based on the well rock type curves and the sedimentary facies constraint. Based on the relationship between J function and water saturation, the formula of water saturation, porosity, permeability, and oil column height can be obtained by multiple regressions for each rock type. Then, the water saturation is calculated for each grid, and a 3D water saturation model is established. The model can reflect the formation heterogeneity and the fluid distribution, and its accuracy is verified by the history matching

Updating and application for a reservoir geological model of deep-water turbidites: A case study of a 4D seismic survey from the PU Oilfield in Angola

During traditional updating processes of reservoir models, the final optimal modelis mainly selected referring to the historical matching results from individual drilling wells, as there is a lot of uncertainty in the distribution prediction of remaining oil crosswells. 4D seismic survey is one of the important modern methods for oil reservoir monitoring, and it has a strong advantage forguiding the distribution prediction of remaining oil cross wells. 4D seismic monitoring information is incorporated into conventional updating processes of geological models, to improve the updating accuracy of reservoir geological models. Fluid evolution information provided by 4D seismic surveys lends solid basis for developing an iterative update method with 4D seismic monitoring, geological modelling, and reservoir simulating.Results in this study suggests that ①4D seismic dynamic information can help improve the numerical modelling loops; ②4D seismic surveys can provide important evidence for the cross-well model parameter adjustment, which help promote the quantitative monitoring of remaining oil and improve the accuracy of reservoir model predictions. This method has a good application effect in deep-water turbidite reservoirs and has practical significance for the development of numerical modelling loops

A study of petrophysical properties based on digital core technology: A case study of a porous carbonate reservoir in the overseas J Oilfield

Developing overseas petroleum exploration and production businesses is a necessary way to guarantee the energy security in China. However, in evaluating overseas reservoirs or designing development plans, due to lack of the first-hand data, the pore structures and seepage mechanisms cannot be well understood and the evaluation effects are influenced. In this study, with the porous carbonate reservoir of the overseas J Oilfield as a case study, the digital core technology is proposed to analyze the pore structure and seepage mechanism. ①With the thin section images of different flow units as the input data, after preprocessing of the medium filtering and threshold segmentation, the digital cores are reconstructed based on the Markov Chain Monte Carlo numerical reconstruction algorithm. ②The bore throat distribution, pore throat connectivity and porosity of the digital cores are analyzed. ③The lattice Boltzmann method is adopted to perform a single phase and two phase oil-water flow simulation in the digital cores, and the absolute permeability and relative permeability curves are calculated based on the simulation results. The reconstructed three-dimensional digital core can describe the differential characteristics of the pore throat radius distribution and pore throat connectivity of porous carbonate rocks in different flow units. The digital core porosity is highly consistent with the porosity of thin section images, and the digital core permeability shows a good positive correlation with the core permeability, thus conforming to the flow unit of the real core. The relative permeability curves of oil-water two-phase flow simulation show differences in the two-phase seepage capacity of different flow units, which can be used as the input of numerical simulation and the estimation of reservoir recovery. The results of digital core analysis are consistent with the results of physical experiments, thus verifying the reliability of the digital core analysis technique. This study provides a new strategy for reservoir evaluation and seepage study in case of data insufficiency and is valuable for reservoir description and effective development

Fractal Analysis of Microscale and Nanoscale Pore Structures in Carbonates Using High-Pressure Mercury Intrusion

This paper investigated fractal characteristics of microscale and nanoscale pore structures in carbonates using High-Pressure Mercury Intrusion (HPMI). Firstly, four different fractal models, i.e., 2D capillary tube model, 3D capillary tube model, geometry model, and thermodynamic model, were used to calculate fractal dimensions of carbonate core samples from HPMI curves. Afterwards, the relationships between the calculated fractal dimensions and carbonate petrophysical properties were analysed. Finally, fractal permeability model was used to predict carbonate permeability and then compared with Winland permeability model. The research results demonstrate that the calculated fractal dimensions strongly depend on the fractal models used. Compared with the other three fractal models, 3D capillary tube model can effectively reflect the fractal characteristics of carbonate microscale and nanoscale pores. Fractal dimensions of microscale pores positively correlate with fractal dimensions of the entire carbonate pores, yet negatively correlate with fractal dimensions of nanoscale pores. Although nanoscale pores widely develop in carbonates, microscale pores have greater impact on the fractal characteristics of the entire pores. Fractal permeability model is applicable in predicting carbonate permeability, and compared with the Winland permeability model, its calculation errors are acceptable