An experimental study was conducted to investigate the effects of gas flow on sand production. We compared gas flow tests to tests with oil or water flow. In the tests, hollow cylinder Castlegate and Saltwash North sandstone specimens, initially wet or at ambient humidity conditions, were isotropically compressed under simultaneous fluid injection. We carried out both one-phase as well as two-phase flow experiments to simulate important processes encountered in gas fields, like water capillary flow or water-cut. The sand onset results showed that sand onset was delayed in the gas flow experiments. The delayed sand onset, i.e., higher sand onset stress, was related to water evaporation due to gas flow, termed flow-through drying, which strengthens the rock. The sand rate results showed that extensive drying of the rock after long periods of gas flow alters its sand rate behavior. It results in continuous sand production of mostly individual grains and small flakes, owing to low grain cohesion forces in the absence of pore water.
Sand production has been a serious concern for the oil and gas industry. It is responsible for erosion of downhole equipment and the need to dispose polluted sand, wellbore instabilities and, in extreme cases, to loss of wells. Sand production, under certain conditions, can also be associated with positive effects on the productivity of a well due to higher applied drawdowns, hole enlargement and removal of the near well damaged zone. The research efforts focused primarily on sand production in oil and/or brine flow as compared to gas flow. However, sand production in gas producing fields has been receiving increasing attention.
Sand production in cemented formations necessitates the mechanical failure of the rock material. This failure occurs when the shear stresses increase above the plastic yielding of the material due to the stress concentration of the effective stress near a well. After mechanical failure, the hydrodynamic force exerted by the flowing fluid on the failed, plastified material leads to erosion and transport of the rock material from the well leaving breakouts behind.
