Spatial evolution of fluid plumes and rock storage mechanism during deep well injection and storage (DWIS)

The Ordos Basin in China is a promising area for geological storage. However, its underground storage layers require effective monitoring measures to ensure a thorough understanding of the storage process and mechanisms. The fluid migration characteristics during deep well injection and storage (DWIS) were evaluated using microseismic monitoring of reservoir strata in the Upper Permian Shiqianfeng and Low-er Triassic Liujiagou Formations. Monitoring revealed that the injected fluid from the bottom sandstone section of the Shiqianfeng Formation migrated upwards and downwards, eventually concentrating in the main waterflood intervals to develop stabilized storage spaces. The lithological analysis of these intervals confirmed the effectiveness of microseismic techniques for geological monitoring of stored fluids. The sta-bilized storage space was associated with strata characterized by high quartz sandstone content, low clay mineral and cement content, plagioclase feldspar, large sandstone thickness, high maturity, high porosity and permeability, and low compressive strength. Compared with the Liujiagou Formation, the Shiqi-anfeng Formation proved more suitable for geological storage owing to its lower compressive strength and elastic modulus, which is more conducive to the expansion of seepage channels. During continuous injection, fluids migrated into pores and cracks, forming stabilized water-containing spaces. This process occurred in four stages: rapid vertical diffusion, slow vertical concentration, horizontal seepage channels breakthrough, and internal stability adjustment, developing the stabilized water storage spaces in the thick sandstone sections of the Shiqianfeng Formation.