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A method using multi-fluid Eulerian computational fluid dynamics (CFD) model to study the migration of pulverized coal in coal-bed methane (CBM) wellbore is presented in this paper. The study aims to predict the condition of discharging pulverized coal out of CBM wellbore and decrease downhole failures such as low efficiency, pump leakage and stuck pump caused by the deposition of pulverized coal. On basis of production conditions of CBM wells in Ordos Basin of China, the transient model of pulverized coal-liquid two-phase flow in the annulus between sucker rod and tubing is established by CFD software, and the effects of pulverized coal size and well liquid inflow velocity on the output of pulverized coal are investigated. On the process of simulation, the distribution and volume fraction changes over time of pulverized coal in the annulus are analyzed, the critical drainage volume of CBM well for discharging pulverized coal is determined, and the output of pulverized coal in every case is predicted. Based on simulation results, the recycle water supplement technology to cleanout pulverized coal in the wellbore is put forward and tested in CBM field. The satisfactory performances of tests show the validity of the CFD study results and the practicability of the recycle water supplement technology. [ABSTRACT FROM AUTHOR]

Natural gas hydrate (NGH) is widely considered as an alternative energy source due to its tremendous reserves, cleanness and high energy density. During the exploitation process, discharging the gas-liquid phase to the surface for separation not only affects the pump performance but also increases the space requirements of the offshore platform. Taking NGH production test data in South China Sea for example, a downhole spiral gas-liquid separator is designed for high gas-liquid ratio (liquid content is less than 10%) in this paper. The forces of droplets in the separator are analyzed and the CFD model for gas-liquid two phase flow is established. The RNG k-ε turbulence model is used for analyzing the velocity field distribution and the pressure field distribution in the separator. The influence of structure parameters (pitch, cycle number of spiral piece, and the outer diameter of spiral pipe) and scale on the separation performance is investigated. The energy loss increases sharply after scaling in the separator and some necessary measures should be taken to avoid the generation of the sale and the secondary hydrate. Based on steepest ascent design, response surface methodology and particle swarm optimization, the optimal structure of the separator with high separation efficiency 87.26% and low pressure drop 2614.19Pa is obtained. The experimental platform is built for testing the gas-liquid separator. The comparison of numerical simulations and experiments show that the calculation model for the hydrate gas-liquid separation is correct and feasible. The separation device with the optimal structural parameters has good separation performance. • A spiral gas-liquid separator suitable for NGH underground mining is proposed. • The flow field and the separation performance of the separator are analyzed. • A parametric study on the separation effect yields an optimal separator. • The optimal geometry has a better separation performance for NGH wells. [ABSTRACT FROM AUTHOR]

Fault diagnosis of the sucker rod pumping system (SRPS) is a challenging problem in the oil industry. Recently, the computer-aided indicator diagram (ID) recognition techniques are becoming useful measurements to help engineers monitor the wells. However, the slow variation of SRPS state makes it difficult for a well to experience all the fault conditions. Using the IDs collected from other oil wells as training data will lead to a large difference between the distribution of training data and target data because of the interference information including noise and system operation characteristics in IDs. Moreover, the different occurrence probability of each fault leads to the imbalance of training data, therefore the fault tolerance of the diagnosis models will result in lower accuracy in identifying the fault IDs with less training samples. In addition, due to one-off training, the parameters of diagnostic model are always fixed resulting in lack of adaptive ability. To address this issue, an evolutional support vector machine (SVM) method for SRPS diagnosis is proposed. First, to obtain balanced training data with similar distribution to the target data, a novel model describing the working process of SRPS under various fault conditions is established. Subsequently, the static apparent stiffness feature and its extraction algorithm is proposed to fully retain the fault information of SRPS in IDs. Then, the incremental SVM is used to construct the diagnosis model based on generated IDs. At last, the proposed method is verified experimentally through the system parameters and IDs of many wells collected from oilfields, and then some conventional techniques are employed in the comparison studies. The obtained results show that the accuracy of the diagnosis model trained by simulated IDs is 11.2% higher than that trained by collected IDs. Besides, the parameters of proposed diagnosis model can be continuously evolved to improve the diagnosis accuracy and generalization ability. Furthermore, the proposed diagnosis model also has advantages in training efficiency and memory consumption. • A novel model describing the working process of SRPS under various fault conditions is established to generate the training data for diagnosis model. • A novel feature of static apparent stiffness and its extraction algorithm is proposed to eliminate the interference component in indicator diagram. • Incremental algorithm and generated indicator diagram are used to continuously improve the performance of SVM diagnosis model. [ABSTRACT FROM AUTHOR]

It is a wildly accepted approach to study the working mechanism of the single abrasive grain by experiment and numerical simulation to improve the working performance of the milling tool in the development of unconventional oil and gas resources. In this study, a mechanical analysis model and a 2D numerical simulation model of single abrasive grain were established to analyze the working mechanism of the milling tool. Then a milling tool with single abrasive grain and an experimental system for milling tools were developed to verify the numerical results. Also, the working process was recorded by a high-speed camera to analyze the chip formation mechanism and the thermal field was obtained by the 2D numerical simulation model to improve service life. Besides, the influence of different working parameters including weight on bit (WOB) and rotating speed was conducted to improve efficiency and safety of the milling tool. Study results indicate that the error between simulation and experiment is within 7.43%, which verifies the accuracy of the 2D numerical simulation model. Both the chips of simulation and experiment are jagged chips without cooling and the error of the chip morphology is only 5.88%. The temperature on the cutting edge increased faster than other positions with some fluctuation while that on the rake face reached a peak at 658.5 °C with some fluctuation. These studies are significant for the design and application of the milling tool with high performance. A mechanical analysis model and a 2D numerical simulation model of single abrasive grain was established to analyze the working mechanism of the milling tool. Then a milling tool with single abrasive grain and an experimental system for milling tools were developed to verify the numerical results. Also, the working process was recorded by a high-speed camera to analyze the chip formation mechanism and the thermal field was obtained by the 2D numerical simulation model to analyze the heat generation mechanism. Image 1 • A analysis model and a 2D numerical simulation model of single abrasive grain were established. • A milling tool with single abrasive grain and an experimental system for milling tools were developed to verify the numerical results. • The working process was recorded by a high-speed camera and the thermal field was obtained by the 2D numerical simulation model. • Influence of different working parameters was conducted to improveworking performance of the milling tool. [ABSTRACT FROM AUTHOR]

Carbon dioxide injection or storage in mature or partially depleted oil reservoirs is an effective way to reduce carbon dioxide emissions and improve oil recovery. However, the corrosion defects greatly reduce the residual mechanical strength of the tubing with the effect of frost heaving force, which seriously limits the carbon dioxide enhanced oil recovery technology widely application. Therefore, the residual mechanical strength of corroded tubing in cryogenic carbon dioxide injection well is investigated in this paper. The results indicate that: (a) The residual mechanical strength of corroded tubing with the effect of frost heaving force is about 68% less than that without frost heaving force. (b) The effect of corrosion depth and location are sensitive, while the corrosion shape is relatively weak. (c) It is a meaningful method to increase working pressure to improve the residual mechanical strength of corroded tubing in the frozen section. • Frost heaving force reduces the strength of the tubing by about 68%. • Corrosion depth and location are more sensitive than corrosion shape. • Increasing working pressure is conducive to improve the residual mechanical strength. [ABSTRACT FROM AUTHOR]

Remote monitoring of sucker rod pumping system (SRPS) based on polished rod dynamometer cards (DC) is an effective means to reduce the operating costs and realize the real-time control. Nevertheless, how to obtain the working process and the production rate of SRPS from polished rod DC is always a puzzle because of complex down-hole motions. The typical solution for this problem is deriving the pump DC via the wave equation to achieve the effective stroke of plunger. But some key parameters involved in this approach such as valve leakage and the fill factor are difficult to determine accurately, especially under fault conditions, which may influence the accuracy of output metering. In order to address this tough issue, in this paper, a novel method of output metering with DC is proposed based on quantitative analysis of fault. The method consists of two parts, the first part is an approach to simulate the working process of SRPS under fault conditions, specifically it's an improved simulation model characterized by a set of fault parameters, which is presented through analyzing the mechanisms of sucker rod pumps at normal and several faulty scenarios. And the second part is a method implemented by genetic optimization algorithm to determine the fault parameters set of the actual SRPS. Using parameters of typical well, the analysis of effects of faults on SRPS is carried out. The simulation results show that valves leakage reduces the flow rate of liquid significantly in the period of effective stroke, which leads to the distortion of output metering results of effective stroke method. Compared with single faults, coupling faults aggravate the production reduction of SRPS. Furthermore, when the well fluid contains gas, the impact of traveling valve leakage on the reduction of production is greater than that of standing valve leakage, but the consequence is opposite when formation energy is insufficient. Besides, the carbon fiber rod and fiberglass rod SRPS are more sensitive to valve leakage, while the steel rod and wire rope SRPS are more sensitive to the condition of insufficient liquid supply. Eventually, the proposed method is verified experimentally through the productive parameters and measured DC of actual wells collected from an oilfield. The obtained results demonstrate the effectiveness of the proposed method for output metering and fault diagnosis as well. Image 1 • An improved model of SRPS is presented to obtain the working process and production rate under fault conditions. • A novel method of output metering with DC for SRPS under fault conditions is proposed based on optimization algorithm. • Field data is adopted to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Fracturing tools such as sliding sleeves, fracturing balls, and ball seats are extensively used for downhole fluid and pressure control. The ball seat is one of the most important components in the multistage fracturing system. After the hydraulic fracturing treatment is complete, the traditional ball seat restricts the production flow and thus must be removed. Extra mechanical interventions are then required to mill out the ball seat after fracturing treatment. In this work, an innovative fracturing ball seat that can be dissolved was proposed and investigated using a controlled electrolytic method (CEM). The newly designed ball seat can be removed through a specific corrosion rate to facilitate an unrestricted flow path for oil and gas production. Comprehensive experiments on the CEM were conducted. The effects of various electrolytic parameters, such as electrolysis current, electrode distance, electrolytes, and tool thickness, on the material removal rate of the ball seat and sliding sleeve were investigated. Experimental results show that the electrolytic parameters significantly affected the electrolytic characteristics. Aluminum alloy is suitable for the manufacture of dissolvable fracturing tool because of its good strength and high electrolytic rate. The study on the newly proposed CEM could provide insights into the design of novel fracturing tools and intelligent well completion systems. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing treatment has been widely applied to simulate oil and gas reservoirs. Ball seat is the most important component in the ball and seat multistage fracturing system. This work aims to study the proppant-carrying fluid two-phase flow and optimize the outlet structure of ball seat. Computational fluid dynamics (CFD) with standard k-ε turbulence model and particle trajectory model is used to simulate the internal flow when fracturing fluid flows across the ball seat. The influence of outlet structure on velocity streamlines, pressure drop, proppant trajectories, proppant concentration and erosion rate are investigated. Compared with the original structure, it is found that the optimized outlet structure with smooth curve can improve the flow status significantly. On-site fracturing experiments have been conducted to validate the CFD study results in a well of Sheng li Oilfield. The experimental results confirm that the optimized outlet structure contributes to lower pressure drop and better erosion resistance. Based on comprehensive analyses, it can be summarized that a general agreement between the numerical simulation and on-site fracturing experiments is obtained. Besides, the obtained results indicate that the CFD approach combining with experimental approach can be an effective method for the design of ball seat and other downhole fracturing tools. [ABSTRACT FROM AUTHOR]

Aiming at solving the problems of small footage, easy skid and immovability of milling during the process of milling multistage fracturing ball seats by milling tools, and considering simultaneously the difficulties of establishing a full-sized simulation model of the milling tool due to the irregular structure and wide variety, a novel method for analyzing the working performance of milling tools based on reverse engineering was proposed to improve the working efficiency on the premise of construction safety. In this paper, a 3D scanning model of the MX97 milling tool was obtained through a 3D laser scanner, and a full-sized simulation model was established based on reverse engineering for finite element analysis. Besides, an experimental system for milling tools was developed to verify the simulation result. Also, the systematic analysis of the influence rule of working parameters on working performance based on the full-sized simulation model was performed, and a selection database of working parameters in the form of charts was established. The analysis results show that the error between simulation and experiment is only 9.9%, which verified the accuracy of the analysis method based on reverse engineering. The surface morphology of the workpiece after simulation and experiment are both circular cuts, and the bottom surface of the milling tool should be designed as an eccentric structure to avoid the zero point of cutting speed that affects the working efficiency. WOB and rotating speed of milling tools affect and interact with each other, which jointly determine the working performance of milling tools. It is necessary to comprehensively use the data from the selection database to accurately determine the working parameters to improve the working performance of the milling tool. • A 3D scanning model of the MX97 milling tool was obtained through a 3D laser scanner. • A full-sized simulation model was established for finite element analysis. • An experimental system for milling tools was developed to verify the simulation result. • A selection database of working parameters was established to improveworking performance. [ABSTRACT FROM AUTHOR]