Fabrication And Research Of Low-Density Proppants Using Lint Clay And Coal Gangue

Proppant is a kind of strong solid particles to support rock seam in the hydraulic fracturing process, whose performance has great influence on supporting fractures, preventing fractures from reclosure and improving oil and gas recovery rate. At present, in order to meet the compatibility with low viscosity clean fracturing fluid, the exploration and development of deep low permeability oil and gas resources including tight oil and shale gas requires proppant to possess low cost, low density, high strength and high crushing ability.In this paper, the ceramic proppants with low density and high strength were fabricated using flint clay and coal gangue as raw materials. The composition and phase of flint clay, tailing and coal gangue were analyzed; the influence of the composition, pulverizing, granulating, sintering and screening on the product performance was investigated; and the relationship between proppant conductivity and particle size and morphology was explored with the aid of X-ray diffraction (XRD) and Scanning electron microscopy (SEM) and broken rate tester. The main research contents and results are as follows:1. Based on the composition and preparation optimization, good-performance and low-density ceramic proppant was prepared successfully at 1400-1450℃ by using flint clay and coal gangue as the raw materials, which meets the industry standards of SY/T5108-2014.2. The properties of flint clay, tailings and coal gangue were analyzed. The results indicate that the main chemical composition of the calcined flint clay, tailings and coal gangue is Al2O3 and SiO2, and the mineral composition is mullite and quartz. The loss of coal gangue is more than 30% during calcination process. The coal gangue are well densified in the range of 1450-1500℃.3. The effect of coal gangue content on proppant performance was investigaed. The results show that the apparent density of the proppant decreases with the addition of coal gangue less than 5%. With the content up to 25%, coal gangue promotes the formation of a large number of closed pores inside the ceramic proppant, so that the apparent density decreases further, and the crushing rate increases. The apparent density of the ceramic proppant was 2.65g/cm3, and the crushing rate under 69MPa was 7.9% with the coal gangue amount of 15wt.% and the sintering temperature of 1410℃. The main crystalline phase is mullite and quartz by XRD analysis.4. The effect of preparation technology on ceramic proppant performance was studied. The results show that the powders with small particle size and uniform distribution are obtained by wet milling process. The surface morphology and strength were improved effectively by adding 0.25wt.% CMC solution as a binding agent and controlling the feeding interval of 180s in the granulation process. The method of pre-screening and screening with a forced ventilation system is helpful for obtain of ball bodies with smooth surface. Raising the sintering temperature promotes the removal of pores and the densification of the bodies, and improving the ability of breaking resistance. However, excessively high sintering temperature may increase the liquid phase, leading to increasing crushing rate.5. The effect of particle state of proppant on its conductivity was studied. The results show that the particle size, distribution, sphericity and surface finish of the proppant affect its conductivity and permeability. Under the same conditions, the proppant with increased particle size, more concentrated distribution, more close to sphericity and better surface finish possesses higher conductivity and permeability.