| Title | Long-term Sustainability of Fracture Conductivity in Geothermal Systems Using Proppants |
|---|---|
| Authors | Earl D. MATTSON, Ghanashyam NEUPANE, Mitchell PLUMMER, Clay JONES and Joe MOORE |
| Year | 2016 |
| Conference | Stanford Geothermal Workshop |
| Keywords | reservoir sustainability, proppants, fractures |
| Abstract | Long-term sustainability of fracture conductivity is critical for commercial success of engineered geothermal system (EGS) and hydrogeothermal field sites. The injection of proppants during stimulation has been suggested as a means of enhancing the conductivity in these systems. Several studies have examined the chemical behavior of proppants that are not at chemical equilibrium with the reservoir rock and water. These studies have suggested that in geothermal systems, geochemical reactions can lead to proppant dissolution and deposition of alteration minerals. We hypothesize that dissolution effects can decrease proppant strength and, thereby, lead to reduced fracture conductivity. To examine thermal and geochemical effects on the geomechanical strength of proppants , we performed modified crushing tests of proppants and reservoir rock material that had been subjected to geothermal reservoir temperature conditions in batch reactor experiments. These preparatory experiments involved heating crushed quartz monzonite rock material and proppants (either quartz sand, sintered bauxite, or kryptospheres) in Raft River geothermal brine to 250 ºC for a period of 2 months. Solid and liquid samples were shipped to the University of Utah for chemical characterization with ICP-OES, ICP-MS, and SEM. A separate portion of the rock/proppant material was subjected to a modified American Petroleum Institute ISO 13503-2 proppant crushing test. This test is typically used to determine the maximum stress level that can be applied to a proppant pack without the occurrence of unacceptable proppant crushing. We use the test results to examine potential changes in proppant/reservoir rock geomechanical properties as compared to samples that have not been subjected to geothermal conditions. Preliminary results may be used to screen proppants for suitability for long-term use in EGS and hydrogeothermal systems. |