Influence Of Mineral Additives On The Properties Of Fracturing Proppant

China is rich in bauxite resources, and bauxite with high alumina content has a wide range of applications in industrial production. Whereas, the utilization of low-grade bauxite resources is relatively low. Consequently, expanding the application of low-grade bauxite resources, and improving resource utilization are of great significance. In the exploitation of oil and gas fields, the fracturing proppant can be used to support oil and gas well hydraulic fracturing the formation of cracks and improve the permeability of flow path of the crude oil, and to help maximize the yield of the oil and gas wells. The fracturing proppant production is mainly prepared from raw materials sintered bauxite.In this paper, fracturing proppant was prepared by pressureless sintering process with starting materials of low-rank bauxite (67wt%Al2O3) and additives of dolomite, pyrolusite and chromite. The influence of different mineral additives on the property of fracturing proppant such as sphericity, bulk density, apparent density, and breakage ratio is studied. Andthe crystal structure and morphology of the sintered samples are analysed by X-ray diffraction (XRD), optical microscopy, transmission electron microscopy (TEM), scanning electronmicroscopy (SEM) and energy spectrum analyzer (EDS). The conclusions are divided into the following several parts.(1) Through the formulation and optimization of the firing system,the fracturing proppant was prepared successfully in the temperature range of1300°C to1480°C using low-grade bauxite as raw materials.All the properties, including sphericity, bulk density, apparent density, and breakage ratio,can meet the SY/T5108-2006requirements according to oil industry standard. And the samples are suitable for deep well operation.(2) The results indicate that the additive of chromite promotes the formation of solid solution of chrome-corundum (Al2-2xCr2xO3,0<x<1) and rod-shape mullite phases, both of which are believed to strengthen the fracturing proppant. Additionally, liquid phase is formed by excessive ferrum located between the ceramic grains at relatively high sintering temperatures, which is important for accelerating the sintering densification.(3) The sintering temperature decreases with the addition of chromite. The optimized proppant sample, which was sintered at1420℃for2h with2wt%chromite doping, shows only a breakage ratio of1.8%under pressure of69Mpa (depressed by64.7%compared with the undoped samples). Furthermore,2wt%chromite doping decreases the sintering temperature by60℃(from1480to1420℃).(4) The addition of dolomite or pyrolusite can effectively reduce the sintering temperature of the sample (approximately100to130℃) through introducing the liquid phase componnet at lower calcination temperature. The breakage ratio of both samples are lower than the undoped sample,37%and43%, respectively.(5) The sphericity, particle size distribution, and phase composition of fracturing proppant did not change significantly with the mineral additives varies.And the microscopic morphology differs from each other.This process enables the production of high-strength fracturing proppant from low-rank mineral materials and demonstrates promise for practical application.