查看更多>>摘要：Permeability is a key factor influencing the recovery of gas resources from gas hydrate reservoirs. During the production process, reservoir permeability increases as the hydrate saturation decreases, which causes difficulties in permeability prediction. However, predictions using classical permeability models do not provide a good match to most of the experimental data. This study proposes a new Cubic model to calculate the permeability increase induced by hydrate dissociation. A series of permeability experiments with variable hydrate saturations were conducted to validate the provide models. Results show that most experimental permeability data points fall between two fitted line segments of the provided models;; i.e. the Cubic pore wall coating and Cubic pore center occupying models. These results also indicate that the behaviors of pore wall coating and pore center occupying hydrates coexist in the process of hydrate synthesis and thus a hybrid growth pattern provides better explain for the experimental and simulated results in this study. Additionally different hydrate growth patterns in the experimental samples reveal that in the reservoirs with low porosity and low permeability, the coating hydrates appear to be more common than center occupying hydrates. The proposed model can be applied to predicting permeability change during gas production, and it also helps understand microscopic hydrate growth mechanisms.
查看更多>>摘要：Directional well trajectory planning, which includes the optimization of the drilling site location and the trajectory between the drilling site to the completion interval, plays an important role in reducing subsea feld development cost. The traditional well trajectory planning methods are based on the projected 2D profle of the wellbore trajectory with empirical knowledge or trial-and-error method to select a proper drilling site. In this study, we propose a new effcient optimization method based on the 3D Dubins curve, which has been widely used in autopilot for path planning but has never been mentioned in drilling industry. In short, we use gradient descent method to fnd the best drilling site location while adopting the 3D Dubins curve as the optimal wellbore trajectory to reach each completion interval so that the “1-site-n-wells” problem can be easily solved. Abundant case studies including both mathematically representative cases and the real practical feld cases are conducted to demonstrate the feasibility and effciency of our method. Wider application of our method for more complex situations are also discussed. This work is the frst of a series of papers which systematically introduce an effcient method for subsea feld layout optimization to minimize the development cost.
查看更多>>摘要：In recent years, thermal non-condensable gas injection was widely used in petroleum industry to enhance oil recovery. However, the research on the heat transfer process and thermodynamic characteristics analysis along wellbore is almost in blank under the condition of cold and hot non-condensable gases simultaneously flowing in wellbore. In this paper, a complicated mathematical model was established considering simultaneous hot and cold gases injected into tube and annulus. Meanwhile, a coupling calculation method was introduced based on temperature equations, pressure equations, and thermodynamic properties. The model can be used to analyze temperature and pressure distribution, the depth of phase transition, the heat transfer pattern and the thermodynamic characteristics. The accuracy of the model was verified and sensitivity analysis of some parameters was conducted. It is found that;; (a) The injection method (hot N2 is injected into tube and cold CO2 is injected into annulus) is optimal, which produces fainter heat loss and maintains higher total energy;; (b) Some factors, such as, the injection temperature, the injection mass ratio of hot and cold gases, and the injection velocity, have a dramatic effect on temperature and pressure distribution, fluid thermophysical parameters, and fluid phase state, (c) According to the calculation results, the optimal temperature of nitrogen is 350 °C, the optimal injection mass ratio of N2 to CO2 is 15:1, and the optimal injection velocity of CO2 is 120 t/d;; (d) The temperature along wellbore changes intensively at the beginning of injection while it becomes stable when the injection time exceeds 10 days. The ingenious coupling model with intricate iterative processes can perfectly simulate the injection process of hot and cold non-condensable gases and obtain the temperature and pressure distribution along wellbore, which can provide tremendous guidance and assistance for injection operations in the oilfield.
查看更多>>摘要：The oil-based drilling fluids are widely used in well drilling. An experimental study on the effect of the addition of silicon oxide nanoparticles of various concentrations on the oil-based drilling fluids properties has been carried out. The range of nanoparticles concentration in drilling emulsions was taken from 0.25 to 2 wt%. The influence of nanosized particles on the viscosity and rheological properties, filtration and antifriction properties, as well as on the colloidal stability of oil-based drilling fluids is considered. This is the first time such a comprehensive study has been carried out. It is shown that the addition of nanoparticles to drilling fluids has a beneficial significant effect on their properties, and even a minute concentration of nanoparticles allowed to observe a change in all parameters. This indicates that the use of nanoparticles can become a promising direction in the field of further improvement of oil-based drilling fluids.
查看更多>>摘要：In oil well drilling, the Annular Pressure Build-up (APB) phenomena may lead to several damages in the formation and, in some cases, the well losing. Open shoes are generally used to mitigate this phenomenon, in which some spaces are maintained opened under the wall coating, at the well bottom. After the fluid expansion and pressure raising, the confined fluid flows directly to the rock formation. The sedimentation of the weighting material in the drilling mud in confined annular regions provides a thicker cake which may clog the shoe, turning the mitigation process inefficient. This research amis to study the effect of previous sedimentation and temperature on the filtrate volume and the mud cake properties for shear-thinning suspensions. To study the particles settlement, the falling dynamics were monitored by an online microscope coupled in a sedimentation test apparatus. Filtration experiments with and without previous sedimentation were performed. It was possible to conclude from experimental data that, for non-Newtonian fluids, filtration and sedimentation rates are increased with previous sedimentation. The main responsible factor is the presence of agglomerated particles vertically chained, increasing the permeability of the sedimentation cake. The observed mechanics are favorable to the annular pressure relief.
查看更多>>摘要：The current study is the first report of estimating kerogen type from petrophysical well logs implementing various machine learning techniques. The methodology is explained through a case study from the Perth Basin, Western Australia. Firstly, the statistical relationships between the petrophysical data (including gamma ray (GR), sonic (DTCO), neutron (NEUT) and density (RHOB) logs) and the Rock-Eval derived hydrogen index (HI) and oxygen index (OI) are investigated. Afterwards, the various machine learning (ML) techniques, including radial basis function (RBF) and multi-layer perceptron (MLP) artificial neural networks, random forest (RF), support vector machine (SVM) and decision tree (DT), are applied to estimate the hydrogen and oxygen index values. Additionally, the MLP network is optimized by the grey wolf optimization (GWO), genetic algorithm (GA) and particle swarm optimization (PSO). The outputs of the various ML approaches are integrated, employing both simple averaging and weighted averaging committee machines. Three statistical parameters of root mean square error (RMSE), mean absolute error (MAE) and correlation coefficient (R) are employed to evaluate and compare the performance of the machine learning ensembles. In general, employing optimization algorithms on the MLP network reinforces the network's performance for the hydrogen index (HI) estimation by increasing overall R and decreasing RMSE and MAE for test data. Likewise, RMSE and MAE values of test data for the oxygen index (OI) decrease using all three optimizers, although R values decrease as well. However, GWO is the most efficient optimizer in diminishing RMSE and MAE and rising R values of test data for the hydrogen index estimation. This algorithm also provides the minimum RMSE and MAE for the oxygen index (OI) estimation. Ultimately, among the proposed intelligent approaches, the weighted averaging committee machine (WACM) provides the maximum correlation coefficient (R) and minimum errors (RMSE and MAE) for both hydrogen index (HI) and oxygen index (OI) estimating. The estimated oxygen and hydrogen indices values are then successfully employed to predict the kerogen types based on the van Krevelen diagram.
查看更多>>摘要：This work systematically studied the significant geochemical heterogeneity of natural gases inside and outside the buried hills of the Xinglongtai area, West Sag, Liaohe Depression, Bohai Bay Basin. The gases inside the buried hills are thermogenic, whereas those outside the buried hills are dominated by secondary microbial gases, with a biodegraded thermogenic gas contribution. The humic-and sapropelic-type gases are primarily derived from the ES3 and ES4 source rocks, respectively. The gases inside the buried hills are primarily derived from the ES3 source rocks, and decreasing δ~(13)C1 and C1/C1.5 ratio towards the northeast are a result of the decreasing maturity of the adjacent ES3 source rocks. The different geochemical characteristics of the gases outside the buried hills results from the relative contribution of secondary microbial and thermogenic gases, the maturity and organic type of the thermogenic gas, and biodegradation. In the Xinglongtai area, secondary microbial gas is an important shallow Paleogene exploration target, and the natural gas inside the buried hills is primarily enriched near the ES3 source rocks. The findings and methods of this work are significant for studies on the origin and accumulation of natural gas inside and outside the buried hills in other petroliferous sags of the Bohai Bay Basin. Considering the geological and geochemical significance of the spatial geochemical heterogeneity of natural gas is essential for researching the origin and accumulation mechanism of gas and oil in complex exploration areas with multiple source rocks.
查看更多>>摘要：Shale oil formations are highly heterogeneous laminated systems containing organic matter (OM). In this study, oil/water flow in laminated shale oil formations are investigated from the pore-scale perspective using the lattice Boltzmann method (LBM). The effects of the pore size and wettability heterogeneities including different pore sizes, contents of OM, wettabilities of OM, and OM distributions on oil/water flow are analyzed. The relative permeability curves of water and oil are calculated and then substituted into the model of numerical simulations to analyze the variations of oil production for each case. Results showed that the relative permeabilities of the mudstone and sandstone laminae are different, and that using the average relative permeabilities of the two laminae can lead to significant errors in the calculation of oil production. With the content and the hydrophobicity of OM increasing and with OM locating in the middle of the mudstone, more oil occupies the pore space around OM and thereby increases the relative permeability of oil (fero) in the mudstone, but conversely decreases kT0 in the sandstone, which in turn affects the proportions of oil production through the mudstone and sandstone.
查看更多>>摘要：Deep learning technology can fit the nonlinear relations between different logging sequences. It solves the prediction problems that cannot be effectively disposed by traditional physical or empirical models. However, these deep learning models lack uncertainty analysis, which affects the popularity of logging prediction models in the petroleum engineering application. In this study, we investigate the nonlinear well logging prediction and uncertainty analysis methods based on recurrent neural network (RNN) with attention mechanism and Bayesian theory. A codec structure model based on gated recurrent unit (GRU) neural network and attention mechanism is established for data prediction. Integrating Bayesian theory into GRU neural network, a GRU Bayesian framework is presented to capture model uncertainty and data uncertainty. The importance of different logging sequences to the predicted goal at the same depth and a certain depth range is considered by using the attention mechanism, which improves the prediction accuracy and reduces the uncertainty of the prediction. Compressional waves sonic log (DTC) data of carbonate reservoir is predicted by using the existing logging attributes (density, spontaneous potential, natural gamma ray and deep investigate double lateral resistivity). Compared with the traditional RNN models, the accuracy of the constructed model has increased by 7.95% (R2 = 93.07%) and the error decreased by 1.7166% (KMSE = 2.9261%) in the field data. More importantly, the proposed method can quantitatively analyze the uncertainties of the predicted results, which effectively heightens the application of the logging prediction model in the petroleum engineering field.
查看更多>>摘要：The Lower Cretaceous Baxigai Formation (K]b) is reservoir for large accumulations of hydrocarbons in the western Yingmaili Area of the Tabei Uplift, Tarim Basin, China. Porosity evolution is a vital influence on reservoir quality. In this study, based on core observation, physical properties, casting thin section, cathodoluminescence (CL), scanning electron microscopy (SEM) and grain-size analysis (GSA), combined with the burial history-thermal history of the Baxigai Formation, the porosity evolution of the K1b sandstone reservoir was quantitatively restored. The K1b experienced early stage of slow shallow burial (with burial depths less than 2400 m) and later stage of rapid deep burial, the diagenetic evolution sequence;; chlorite film→slow shallow burial and compaction→early calcite cementation/anhydrite cementation→ econdary quartz enlargement→late rapid deep burial and compaction→dissolution of feldspar and carbonate cement→kaolinite precipitation→late ferriferous calcite cementation. Based on the pore structure characteristics, the porosity contribution of each diagenetic can be quantitatively calculated, to restore the actual porosity evolution history. The results indicate that two types of reservoirs exist in the Kib. Due to the influence of depositional environments and later diagenetic (for type I reservoirs, Φ_0 = 37.38, moderate compaction and weak cementation;; for type II reservoirs, Φ_0 = 35.95, moderate compaction and medium cementation), the current reservoirs have differential distribution characteristics. Effective porosity (greater than 15%) of the reservoirs during the two hydrocarbon accumulation periods promoted the formation of oil and gas reservoirs.
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