Abstract: Lower Wuerhe reservoir of District No.8 in Karamay oil field is a thick massive ultra-low permeability conglomerate reservoir, and was developed by waterflooding process with inverted nine-spot pattern and well spacing of 275 m in one series of strata in early stage. But it featured such poor development effects as the low efficiency of response for producers, low pressure maintenance degree and low oil production rate. The low permeability reservoir and larger producer-injector well spacing should be the main reasons for it was hard to establish effective waterflood response. This paper presents the close spacing pilot test that is to establish effective waterflood system by subdividing the layer series of development, decreasing the well spacing and changing the well patterns. The layer series of development is subdivided into three layers and recompleted layer by layer. The WU-4 unit is the first layer to be tested. The inverted nine-spot well pattern is infilled from 275 m×388 m to 138 m×195 m in the first stage and then converted into five-spot pattern to take a waterflood along parallel fractures, while controlling the injection flow rate by strategy of water drive weak at the spot and intensive in the area. Three- year test has shown that the production indices are all better than the original ones before, and it is expected that the recovery factor will be increased by 8.5% by this test.

Key words: Karamay field, conglomerate reservoir, low permeability, close spacing test, infill well, layer series of development