Evaluation of permeability damage caused by drilling and fracturing fluids in tight low permeability sandstone reservoirs

Tight sandstone reservoirs with low porosity and permeability are always vulnerable to damage due to drilling and fracturing fluids, which significantly impedes hydrocarbon production. Therefore, exploring damage evaluation methods has been an undeniable demand of formation protection and efficient development. However, the common steady-state core flow method is time-consuming and inaccurate for evaluating permeability damage in tight low permeability reservoirs. Aiming at this problem, this paper introduced pressure transmission test (PIT), a time-saving and accurate method, to quantitatively evaluate the core permeability damage degree from macroscopic perspective. Furthermore, nuclear magnetic resonance (NMR) was also used to analyze the damage mechanisms of fracturing fluids from microscopic perspective. In the fracturing fluids damage experiments, the results of PTT show that the ultimate damage degree of fracturing fluids is approximately 40%, of which water-sensitivity, water-block, and solid-phase are approximately 10%, 12% and 16%, respectively. With the technique of NMR, the damage mechanisms due to fracturing fluids are also investigated. In the drilling and fracturing fluids damage experiments, the results of PIT show that the drilling fluids cause the major damage. In the experiments of acidizing treatment, the chelating acid shows excellent properties in reliving core permeability damage caused by drilling and fracturing fluids. This study provides a new idea for evaluating permeability damage in low permeability reservoirs, such as shale, tight sandstone reservoirs, bedrock reservoirs, and so on.