Influence of fractures on the development of low-permeability sandstone reservoirs: A case study from the Taizhao district, Daqing Oilfield, China

摘要

This paper studies the influence of fracture on the development of low-permeability sandstone reservoirs. There are four assemblages of high angle tectonic fractures assuming east-west, south-north, northwest-southeast and northeast-southwest strikes respectively in the Putaohua oil layer of the Taizhao district, leading to a gradual weakening in their development. In light of the influences of the present-day stress field, the east-west fractures are considered to have the best connectedness, the biggest aperture, the highest permeability and the lowest opening pressure, present the main channel for fluid flow in the low-permeability sandstone reservoirs. These fractures impact on the well pattern deployment, water injection and hydraulic fracturing in the low-permeability sandstone reservoirs. Based on the distribution and flow characteristics of fractures, favorable effects can be obtained by rectangular and rhombus well patterns along the principal seepage fractures of the east-west orientation in the primary period of development. Due to their minimum opening pressure, the east-west fractures are the earliest to open during the water flooding development, so we should control the injection pressure under the open pressure of east-west fractures. Artificial fractures formed by hydraulic fracturing in low-permeability sandstone reservoirs are controlled by natural fractures and the presented-day stress. If the angle between natural fractures and the present-day stress is less than the critical angle, the artificial fractures extend mainly along the natural fractures and do not generate new fractures. If the angle between natural fractures and the present-day stress is bigger than the critical angle, the artificial fractures extend vertically to the minimum stress (σ3) of the present-day stress field. These results demonstrate the importance of assessing the fracture distribution in the low-permeability sandstone reservoirs.