Synchronous injection-production energy replenishment for a horizontal well in an ultra-low permeability sandstone reservoir: A case study of Changqing oilfield in Ordos Basin, NW China

Abstract

It is difficult to build an effective water flooding displacement pressure system in the middle section of a horizontal well in an ultra-low permeability sandstone reservoir. To solve this problem, this study proposes to use packers, sealing cannula and other tools in the same horizontal well to inject water in some fractures and produce oil from other fractures. This new energy supplement method forms a segmental synchronous injection-production system in a horizontal well. The method can reduce the distance between the injection end and the production end, and quickly establish an effective displacement system. Changing the displacement between wells to displacement between horizontal well sections, and point water flooding to linear uniform water flooding, the method can enhance water sweeping volume and shorten waterflooding response period. The research shows that: (1) In the synchronous injection and production of horizontal well in an ultra-low-permeability sandstone reservoir, the water injection section should select the section where the natural fractures and artificial fractures are in the same direction or the section with no natural fractures, and the space between two sections should be 60–80 m. (2) In addition to controlling injection pressure, periodic water injection can be taken to reduce the risk of re-opening and growth of natural fractures or formation fracture caused by the gradual increase of water injection pressure with water injection going on. (3) Field tests have verified that this method can effectively improve the output of single well and achieve good economic benefits, so it can be widely used in the development of ultra-low permeability sandstone reservoirs.