Changes in the engineering properties of sands due to fracturing of grains at high pressures

Cambios en las propiedades ingenieriles de arenas por fracturamiento de granos a altas presiones

Abstract

The fracturability of grains from different fractions of a clean non-siliceous sand from crushed rock impregnated with two fluids with different viscosities and initial moisture contents of 0%, 3%, 6% and flooded (≈99%) was studied. evaluate the influence of both viscosity and moisture content on said fractureability. The fractions were i) well-graded original complete sand, ii) coarse (P#4-R#10), iii) medium (P#10-R#40) and iv) fine (P#40-R#400). Samples of these fractions were tested in a consolidometer until reaching a maximum pressure of 127.3 kg/cm2. Some tests were stopped at 56.6 kg/cm2 to evaluate fractureability at that pressure with both fluids. Then, identical tests with these same fractions were carried out at the maximum pressure. The results show that both viscosity and humidity alter the volume change patterns at both pressures for both sand fractions. Changes were observed both in the slopes of the consolidation curves and in the void ratio at the end of the tests. The initial humidity of the tests changes the fracture patterns of the sand fractions with increasing pressures. Consequently, the initial humidity also influences the final specific surface area of the different fractions and their hydraulic conductivity at the same pressures. It was observed that samples with high void ratios and moderate specific surface area have lower hydraulic conductivity than others with lower void ratio but lower specific surface area. This is because as the stress increases, both the fracturability and the void ratio change. Therefore, hydraulic conductivity is a very complex variable and difficult to predict. The use of parameters obtained with oven-dried sands can lead to significant errors in their estimates for applications in oil production processes.