Abstract
Complex geology and fracturing operations have led to frequent sand production problem in the shale gas well. Sand production brings huge engineering risks and seriously affects the normal production of the shale gas well. In order to study the property and source of the yielded sand, sand samples in three production periods of flowback, production test and gas production are collected from Sichuan Basin of China. Combining the methods of particle size analysis, microscope observation, scanning electron microscope, CT scanning, infrared spectroscopy and energy dispersive spectrum analysis, the multi-scale structure and composition characteristics of the yielded sand from different production periods were investigated. Results show that the sand size is the largest in the production test period and the smallest in the gas production period. The large-size sand is blocky in the flowback period, while it is flaky in the period of production test and gas production. The roundness of sand becomes worse as the sand size decreasing. Sand composition has the characteristics of fracturing proppant and shale mineral. Cementing material between large-size sands has the network structure and the higher content of aluminum and iron. Organic chemicals are found to be adhered to the sand surface in all three periods. Both shale fracture and proppant failure can generate particles that provide the material source for sand production. This research provides the source of the yielded sand and a theoretical guidance for the sand production mechanism.
Highlights
Staged fracturing of the horizontal well is the dominant technology for commercial exploration of shale gas, but the consequent problem of sand production has become an inevitable problem in oil and gas exploration
The 3# sample is yellow coming from the well in the gas production period with a mass of 378.00 g, and this well was fractured into 89 stages using
These results indicate that the particle size of the yielded sand in the period of production test is dominated by large–size sand with good roundness, while the small–size sand is mainly in the period of gas production
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Drilling into reservoirs and exploration of oil and gas can cause redistribution of stresses in the formation, and changes in stresses often result in rock failure that can trigger sand production. During oil and gas exploration, scholars have used the stress redistribution caused by oil and gas exploration to obtain a formation fracture model and critical production pressure difference for predicting sand production [7,8]. Sand production caused by fluid action is often considered a negative factor in oil and gas exploration, but it can have a positive effect in heavy oil exploration [9]. Computational Fluid Dynamics-Discrete Element (CFDDEM) coupling method is used to study liquid-induced erosion in loosen formation and found that increased axial pressure exacerbated erosion and increased radial pressure caused continuous sand production [14]. Base on the results of experimental evaluation and theoretical analysis, the formation mechanism and influencing factors of the yielded sand was demonstrated
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