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The well performance in Coal-Bed Methane (CBM) reservoir is highly dependent on the conductivity of hydraulic fracture created to increase well production rate and contact area with the reservoir. Aimed at improving the effective fracture length of hydraulic fracture in CBM reservoir and the seam proppant concentration, the objective of this paper is to investigate the migration of variable density proppant particles in hydraulic fracture and seams using numerical modeling and simulation. In the proposed model, the interaction among fracture proppant particles distributed in a pseudo fluid model is taken into consideration. Comparison between the model calculation and field radioactive tracing logging interpretation shows that the proposed model is accurate and reliable in applications. Additionally, we carried out the sensitivity study on the viscosity of fracking fluid, fracture area, proppant density, injection rate and other factors. It is shown that, with the condition of a confining pressure of 69 MPa and an ambient temperature of 90 °C, the crush value of nutshell proppant is less than 2%, which meets the field application requirements. Furthermore, with the increase of both fracturing fluid viscosity and injection rate, the propped effective fracture length increases, and lead to a more uniform distribution of proppants. The increase in proppant particle diameter, inversely, results in a decrease in the effective fracture length. As for variable-density proppant, the effective crack support length would be longer than the single ceramic proppant, and the particle distribution of the case with variable density is more uniform. [ABSTRACT FROM AUTHOR]

Shale gas development in the Sichuan-Chongqing region in China has experienced a high level of casing deformation or failure during hydraulic fracturing treatment, which has resulted in significant productivity decline and economic losses. This problem has motivated many studies in the literature but focusing on the shearing deformation using the finite element method. This paper categorizes the casing failure modes and mechanisms in the region and presents casing collapse laboratory results. The designed laboratory tests rendered us critical data points in casing deformation under different loading scenarios. For multiple stage hydraulic wells in the region, we propose to use a strain-based protocol for casing design instead of the current design based on maximum stress. • Present laboratory experiments on casing deformation due to shearing stress. • Propose a model to predict the maximum allowable stress for a casing tubular. • Update statistics on casing deformations and failures in the Changning-Weiyuan region. • Introduce one of a kind laboratory experiment setup for full size tubular testing. [ABSTRACT FROM AUTHOR]

Casing failure during hydraulic fracturing is infrequent, but its consequence and impact can be significant for the shale gas wells. It may result in inaccessible cased hole and environmental and safety concerns over wellbore integrity during the shale gas reservoir development. Based on theoretical analysis, numerical simulation and field measurement, the failure mechanisms of casings in shale gas wells are revealed. Through parametric sensitivity analysis, the countermeasures are recommended. Results indicate that one of the casing failure mechanisms in shale gas wells is shear deformation induced by the slip of shear fractures. The simulated casing deformation is consistent with the lead impression. Casing curvature is introduced to assess the traveling capability and casing integrity. The maximum curvature is significantly larger than that of normal directional borehole, which causes the resistance of downhole tools passing through casing. Decreasing the crossing angle and employing the cement with a low Young's modulus or even no cementing can be the effective measures to prevent casing failure in this mode. The research findings provide new evaluation criterion and controlling methods for casing integrity in shale gas wells under hydraulic fracturing. [ABSTRACT FROM AUTHOR]

Erosive wear due to particle impact serves as the main cause of pipeline failure. During hydraulic fracturing, fracturing pipelines inevitably suffer erosion damage under high fluctuating stress. In this study, a novel erosion test rig was developed in order to reproduce erosion scenes under complicated fracturing conditions. Then the erosion experiments involving fluctuating stress were carried out for the first time, and the erosion characteristics under varying conditions were obtained. In the erosion tests, the impact angles of the slurry flow varied from 15° to 90°, the flow velocities varied from 7.5 m/s-20 m/s, the solid particle concentration was 10% (in wt.%). The target material was 35CrMo steel, and the flat tensile specimens of 4 mm thickness were used in all erosion tests. Furthermore, the erosion mechanism with consideration of applied stress was subsequently revealed according to micro-structural characterization as well as the rheological spring-slider model. The complex erosion behavior of fracturing pipelines under severe conditions was well unraveled at the laboratory scale. • A new erosion test rig capable of applying fluctuating stress was developed. • A series of erosive wear experiments involving fluctuating stress were performed. • Fatigue cracks were observed in the eroded area during erosive wear. • The stress-erosion mechanism was revealed with the consideration of rheological theory. [ABSTRACT FROM AUTHOR]