查看更多>>摘要：This is the second part of our study on the resistivity curve responses of marine shale gas reservoirs. The characteristics of the effects of low-porosity systems on electrical conductivity have been explored previously. However, the effects of the pore system and reservoir type should also be carefully considered. The features of the pore system that have the greatest impact on resistivity must be identified so that they can be considered in subsequent studies. This paper shows that the pore type has the most direct effect on the rock resistivity. The relationship between the porosity and resistivity of each pore type is very close. The pore types must be distinguished when considering the application of shale conductivity features. Among the reservoir classification methods considered, those based on reservoir quality characteristics and clustering have the best correspondence with the resistivity curve. In addition, this paper shows that the existing common saturation models are insufficient to evaluate the saturation of shale gas reservoirs. Subsequent research, including the derivation of conductivity models or the performance of shale resistivity experiments and simulations, should fully consider the characteristics of the mineral composition, organic matter and pore types of the rock. This series of analyses paves the way for research on shale gas electrical conduction mechanisms and saturation models, which are for the study of shale gas reservoir petrophysics. This study helps to address the lack of deep rock geophysical research on the large shale gas reserves that have been discovered.
查看更多>>摘要：CO2 huff and puff (HNP) is one of the most effective methods to improve tight oil recovery after the primary depletion process. The seepage mechanisms between CO2 and crude oil are complicated in porous media during CO2 HNP process. Therefore, in this paper, the CO2 HNP process of Chang-7 tight oil reservoir, Ordos Basin, China, was studied by nuclear magnetic resonance (NMR) technology, microscopic observation and numerical simulation. Experimentally, using NMR technology and microscopy methods, the distribution characteristics of residual oil during CO2 HNP process were measured intuitively. Numerically, a group of core-scale and field-scale simulations considering molecular diffusion and asphaltene precipitation were established to further verify and elongate the experimental results. The results show that at the initial state, the crude oil in the tight core was mainly distributed in nanopores, sub-micro-nanopores and sub-micropores, where the oil content exceeded at least 73% in these pores. During CO2 HNP process, the oil recovery was more pronounced for the 1st and 2nd rounds than for 3rd to 5th rounds. Notably, even if the cores with more nano-pores were more favorable for the 4-5th CO2 HNP rounds, the oil molecules in nanopores were still difficult to be available. Moreover, the CO2 sweep scope could be divided into displacement affected region and diffusion affected region. CO2 could effectively drive the crude oil in the displacement affected region. While the oil could be successfully displaced by dissolved gas flooding in the diffusion affected region only under the appropriate conditions. Meanwhile, the core-scale numerical models confirmed that it was necessary to consider molecular diffusion and asphaltene precipitation factors, which would make the simulation results in line with the experiment. In terms of the ultimate oil recovery, the field-scale model only considering the diffusion (2.456%) > the model both considering the diffusion and asphaltene (2.436%) > the model without considering the diffusion and asphaltene deposition (2.412%) > the model only considering the asphaltene deposition (2.388%).
查看更多>>摘要：The relative permeability of immiscible multi-phase flow in Layered 2D porous media is investigated employing the diffuse interface Lattice Boltzmann model. The interfacial tension is set to small value to mimic the near miscible condition of the fluids. The model is validated with static and dynamic analytical solutions. Three classes of porous media are examined;; A high permeable porous media, a low permeable porous media, and layered dual permeable porous media. For the later case, parallel and serie conditions were considered. For each condition, three proportion of layers were studied;; I-25% of the high permeable layer, II-50% of the high permeable layer, and III-75% of high permeable layer. For each condition, the viscous coupling effects due to viscosity ratio, the capillary number and the effect of the fluid patterns on the relative permeability curves were investigated. The simulation results showed very small errors compare with the analytical permeability solutions of layered porous media. The findings showed that despite the dual permeable serie system, the relative permeability curve of dual permeable parallel geometry is closely matched with the analytical solution.
查看更多>>摘要：Production optimization is an effective technique to maximize the oil recovery or the net present value in reservoir development. Recently, the stochastic simplex approximation gradient (StoSAG) optimization algorithm draws significant attention in the optimization algorithm family. It shows high searching quality in large-scale engineering problems. However, its optimization performance and features are not fully understood. This study evaluated and analyzed the influence of some key parameters related to the optimization process of StoSAG including the ensemble size to estimate the approximation gradient, the step size, the cut number, the perturbation size, and the initial position by using 47 mathematical benchmark functions. Statistical analysis was employed to diminish the randomness of the algorithm. The quality of the optimization results, the convergence, and the computational time consuming were analyzed and compared. The parameter selection strategy was presented. The results showed that a larger ensemble size was not always favorable to obtain better optimization results. The increase of the search step size was favorable to escape from the local optimum. A large step size needed to match a large cut number. The increase of cut number was beneficial to increase the local searchability, but also made the algorithm more easily fall into the local optimum. The random initial position was beneficial to find the global optimal point. Moreover, the effectiveness of the parameter selection strategy was tested by a classical reservoir production optimization example. The final net present value (NPV) for water flooding reservoir production optimization substantially increased, which indicated the excellent performance of StoSAG by adjusting the key parameters.
查看更多>>摘要：To study the scaling process in sub-sea pipelines, a mesoscale experimental loop was developed, it was used to generate inorganic salt deposition in a one-inch diameter pipe. A specially monitored test section was developed, it would be removed and weighed after the experiments to study the scale build-up over time. Changes on the experimental conditions such as flow rate and fluid concentration allowed us to understand how calcium carbonate accumulation affects pipeline surfaces over time. The calcium carbonate concentration of the fluid passing through the pipe was controlled using a turbidity meter. The size of the loop, a novelty on the field, allowed us to generate extensive data on the calcium carbonate scaling process, conduct longer experiments, and visualize smaller changes in temperature or accumulation using non-intrusive infrared (IR) technology. The experiments were conducted using IR images and chemical analyses by Energy dispersion X-ray spectroscopy (EDS) and the results were compared with predictions from analytical models.
查看更多>>摘要：The continuous-wave mud pulse telemetry is currently one of the most advantageous methods for wireless downhole transmission. The rotary valve orifice of a continuous-wave mud pulser must be optimized to generate highly similar sinusoidal pressure waves for high-speed and reliable transmission. In this study, an improved fan-arc-straight-based valve orifice is designed based on a general fan-based valve orifice by analyzing the relationship between throttle area and relative rotation angle of the rotor/stator on the basis of thin-walled cutting edge differential pressure generation mechanism. Then, CFD simulation studies are investigated. It is indicated that the peak-to-peak value of the differential pressure is proportional to the square of the inlet flow;; and with the increase of axial clearances between the stator and rotor, the peak-to-peak values of the differential pressure signals show a negative exponential decrease trend, while the correlation coefficients also decrease monotonously. Furthermore, surface hydraulic system experiments have also been implemented;; and the actual 8 Hz and 12 Hz pressure waves with correlation coefficients greater than 0.99 are obtained compared with the corresponding sinusoidal signals. It is believed that the optimized valve can achieve highly similar sinusoidal pressure waves with acceptable amplitudes during practical operation to meet the field operation requirements.
查看更多>>摘要：With the acceleration of deep oil and gas development, the problem of high temperature and high salinity in the formation is prominent, which seriously affects the rheology and filtration performance of water-based drilling fluid and causes drilling accidents such as formation collapse and wellbore instability. Therefore, in this work, a novel thickening and fluid loss control additive (i.e., ASML) with significant hydrophobic association characteristics as well as outstanding temperature-and salt-resistance was synthesized using acrylamide, sodium p-styrenesulfonate, maleic anhydride and lauryl methacrylate as monomers. The experiments of fluorescence spectroscopy, SEM, Zeta potential, rheology and filtration show that ASML makes the drilling fluid have more networked structure under the conditions of high temperature and high salt through hydrophobic association. At the same time, it also brings more negative charge to the bentonite by adsorbing ASML on the surface of bentonite, which effectively maintains its uniform colloidal dispersion, leading to higher viscosity, denser mud cake, and lower fluid loss under high temperature and high salinity conditions. Under the condition of 200 °C and 30 wt% NaCl, the fluid loss of ASML-based drilling fluid is only 5 ml, which is 94.3% lower than that of carboxymethyl cellulose-based drilling fluid. This study provides a new strategy for the development of temperature-and salt-resistant drilling fluid treatment agent, which is important for accelerating the efficient development of deep oil and gas.
查看更多>>摘要：Heavy oil wells in Talie oilfield are exploited by injecting light hydrocarbon mixing into annulus to reduce viscosity, and system efficiency prediction is of great significance for the evaluation of the energy consumption and management level of the production system. However, system efficiency of the pumping unit well with light hydrocarbon mixing (PW-LHM) is affected by many factors, and it is difficult to use traditional methods to make comprehensive evaluation and quantitative prediction. In order to accurately predict the system efficiency and evaluate the viscosity reduction effect, this paper used the Pearson correlation coefficient analysis method to analyze the correlation between production data, diluting attributes and system efficiency, and principal component analysis (PCA) was utilized to conduct data dimension reduction and controlling parameters determination. Considering the change trend and correlation of the artificial lifting equipment and mixing equipment working conditions, a time series prediction model for system efficiency was established based on the long short-term memory (LSTM) algorithm. Filed application results show that the prediction model based on LSTM can perform accurate prediction of the system efficiency, early forewarning of the production conditions and timely adjustment of the lifting and mixing parameters of the PW-LHM.
查看更多>>摘要：Scholars have conducted in-depth research on the seepage mechanism of oil and gas reservoirs, large-scale fracturing well productivity simulations, and reservoir phase behavior simulations, and corresponding models have been developed. However, models for calculating the productivities of fractured horizontal wells considering phase changes have not been reported. In this study, the productivities of fractures in a horizontal well were assumed to be unequal. The productivity equations for horizontal wells reported previously were modified and combined with the Peng-Robinson equation of state to describe the productivity in an actual production process. An example calculation showed that the number of fractures and the fracture conductivity have significant influences on the productivity. When the bottom hole pressure was 0.1 MPa, taking the fractured horizontal well with four fractures as an example, the tip pressure of the fourth fracture was 67.63% higher than that of the first fracture. The productivity contribution rate reached 30.48%. Using the proposed equation, we can calculate the open flow rates of gas wells and the amount of condensate oil in the fractured horizontal well gas reservoir's development process. This paper provides a reference for the selection of the gas reservoir production mode and the optimization of the fracture parameters.
查看更多>>摘要：As an enhanced oil recovery method, the air injection process (AIP) has been applied for decades. However, deviations are still being identified between laboratory tests and field applications. One possible reason for such deviations is the formation minerals of the crude oil reservoir. Some natural minerals are beneficial for the oxidation of hydrocarbons and may affect the AIP behavior. Herein, the accelerated-rate calorimetry (ARC) was adopted to study the crude oil oxidation when containing pyrite or iron oxide under adiabatic and high-pressure conditions. The temperature profiles and detailed kinetic data from the ARC tests were compared for the crude oil oxidation traits, with different ground mineral particles presented in the ARC vessel, to figure out the catalytic effects of iron minerals on the crude oil oxidation. Results indicate that iron oxide showed a catalytic effect on the high-temperature oxidation period of crude oil, whereas the pyrite could not generate enough iron oxides to catalyze crude oil oxidation under limited oxygen conditions. During the test, since pyrite oxidizes before the crude oil, the enthalpy from pyrite oxidation could benefit the onset of crude oil oxidation. Hence, this study could be beneficial for future AIP engineering design and AIP candidate reservoir screening.
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