Over the last decade a rapid increase in utilization of unconventional reservoirs ha occurred due to advances in horizontal drilling and multi-stage fracturing technology. Reservoirs that earlier were far beyond commercial reach are today producing oil and gas in competitive manner. The share of energy provided form unconventional reservoirs is projected to keep growing relative to conventional energy sources in the years to come. Proppants are essential component in hydraulic fracturing operation as they are placed in fractures and offers increased permeability for the relative impermeable rock- formations present in unconventional reservoirs. Production efficiency may be improved by altering proppants in terms of: mechanical, physical, reactive, and geometrical properties.
Development of strong nano- porous material for proppant applications opens the possibility of multi- functional proppant- solutions. A proppant material with high surface area applied in high temperature reservoirs may enable catalytic reactions on proppant surfaces and thereby in- situ upgrade hydrocarbons. Proppant with high degree of open porosity can enable proppants to be impregnated with surfactants that reduces friction between proppants and oil migrateing through the interstitial void space between particles during operation. Because of high closure- stress occurring in fractures, the most important proppant-material property is high mechanical strength.
Experimental objectives were to adjust synthesis parameters and modification methods to achieve best possible combination of tensile strength, open porosity and high surface- area. Nano- porous γ-alumina spheres modified by impregnation of a magnesium oxide precursor and subsequent calcinations is under current investigation. Impregnations of alumina spheres were carried out using two different methods. Traditional incipient wetness impregnation was carried out in addition to more experimental approach using ultrasonic waves to aid impregnation.
Results show that α-alumina + MgAl_2 O_4(spinel) evolved from modification treatment after high temperature calcinations. By applying uniaxial compression tests and Weibull analysis it is clear that current reaction significantly improves the mechanical performance of the material. Ultrasonic impregnation proved more effective to obtained increased mechanical performance compared with incipient wetness impregnation. A trade-off between surface area and tensile strength is apparent for modified material. However one sample proved it possible to obtain strengths sufficient enough for proppant application in combination with open pore volume and surface area. Small MgAl_2 O_4(spinel)- crystallite sizes is required to retain surface area and open porosity after high temperature calcinations. The mechanical performance is more dependent on homogeneous distribution of precursor during preparation, than impregnated nominal metal oxide- concentration and final crystallite sizes.
It is suggested that pore diameters and size distribution governs precursor distribution along with local metal oxide concentrations deposited during preparation and drying. Current work illustrates that it is possible to develop materials that fulfills requirements for multifunctional proppant applications. Results also imply that further improvement of the desired material properties is within reach.
Keywords: Proppant, catalyst support, spinel, incipient wetness impregnation, ultrasonic impregnation, Weibull analysis, crush resistance uniaxial compression, tensile strength, stress distribution, nano- porous, alumina, spheres, mechanical performance, metal oxide distribution, pore diameters, pore size distribution, surface area, open porosity, proppant requirements
Institutt for materialteknologi , 2014. , 82 p.