Papers by Author: Yu Huan Bu

Abstract: In this article, we prepare the physical model with the high density epoxy resin and different sizes of coin shaped silicone pieces which can simulate the directional arrangement of fracture medium. On the basis of this, we analyze the influences of fracture angle on the ultrasonic compressional wave velocity using the pulse transmission method and compare the experimental results with the Hudson effective medium model. The experimental results show that, velocity decreases linearly with the increase of fracture angle within the interval of [0°~90°]. In a similar aspect ratio and same angle case, the increase of fracture porosity will result in the decrease of the velocity which is weakened by the increase of fracture porosity. At high fracture porosity, fracture angle becomes the important influence factor on the velocity changing. The calculation results of the Hudson model have a small deviation which is less than 5% compared with the experimental results but show a difference in different angle interval. The combination of the two methods will provide a certain basis for the indoor experiment and the measurement of the velocity in field.

Abstract: Particle morphology which affects the packed state of particles is a factor that cannot be ignored in the study of gradation model. Floating beads, as the most commonly lightweight additive used in cement slurry, are always regarded as ideal spherical particles, thus the effects of its circular degree on close packing are overlooked. In order to quantitatively characterize the circularity of floating beads , based on image processing methods of powder particles, combined with image processing software(Photoshop and MATLAB), replaced the watershed segmentation method with removing linking particles, the calculating method of the circularity of powder particles was put forward, and finally the average circularity of floating beads was obtained (about 0.929＜1). Although floating beads have high spherical degree, they still aren’t ideal spherical particles, so their morphology feature should not be ignored in the study of particle size distribution.

Abstract: In view of the complicated issue that how to improve the cementing quality of the second interface in cementing engineering, experimental and theoretical research on slag MTC slurry improving the quality of the second interface was carried out in the paper. Experimental study shows that slag MTC and mud cake can achieve overall cementing; the volume shrinkage ratio of slag MTC is far less than the cement slurry system; and the strength of slag MTC cannot be affected by the presence of mud cake and is greater than low-density cement slurry. Theoretical analysis shows that the alkali activator and Ca(OH)₂ produced by hydration can react with SiO₂ which exists in mud cake and dead mud to get C-S-H gel with a low ratio of calcium to silicon, and improving the quality of the second interface. The study on the chemical shrinkage ratio of the products of slag MTC hydration was made by using the method of chemical analysis, and low-shrinkage mechanism of MTC was revealed. The results show that mud cake solidification, dead mud solidification and low-shrinkage ratio are fundamental to improve the cementing quality of slag MTC and formation.

Abstract: The fluid loss control additive plays a key role in reducing reservoir damage and improving the cementing quality of an oil well. Aiming at good fluid loss control ability and excellent dispersibility, a new dispersive type fluid loss control additive was synthesized through orthogonal experiment with 2-acrylamido-2- methyl propane sulfonic acid, acrylamide, N, N-dimethylacrylamide and maleic anhydride. The orthogonal experiment result shows that the influence on the properties of FLCA decreases in the order: PH value > monomer concentration > monomer mole ratio > initiator concentration > temperature. The result indicates that the optimal conditions for FLCA were 4/2.5/2.5/1 of mole ratio of AMPS/AM /NNDMA/MA, 32.5% total monomer concentration in deionized water, 1.0% (by weight of monomer) ammonium persulfate/sodium bisulfite, 4 of PH value, 40°Cof temperature. The synthesized copolymer was identified by FTIR analysis. The results show the dispersive type fluid loss control additive has excellent dispersibility, fluid loss control ability, thermal resistant and salt tolerant ability. As the temperature increases, the thickening time of the slurry containing the synthesized additive reduces. The copolymer is expected to be a good fluid loss control additive.

Abstract: Crack universally existing underground is an important kind of pores. In order to study the elastic wave propagation in fractured medium through experiment, a new method to make artificial core with certain cracks using oil well cement and camphor sheet or thin steel sheet is put forward. Geometric parameters of the crack, such as shape, size and aspect ratio, are approximately equal to that of camphor sheet or thin steel sheet. Using the thin steel sheet to make crack can be more easy and accurate to control the crack angle than using camphor sheet. The crack opening scales at millimeters. The aspect ratio of cracks formed by camphor sheet ranges from 1.4 to 8, and aspect ratio of cracks formed by thin steel sheet ranges from 2.5 to 70. This method is proved simple and feasible by experiment practice, which can provide artificial cores with certain crack for acoustic wave propagation study.