With the increase of CSS cycles and decline of production, some reservoirs cannot be converted to steam flooding or SAGD production due to their characteristics, limiting the development effect of this kind of reservoirs. Therefore, steam flooding has been combined with SAGD on a trial basis, forming the gravity water-drainage assisted steam flooding technique, which has successfully solved the problem of how to produce this kind of reservoirs at their later production stage. The technique uses the combination of vertical wells plus horizontal wells. A paired horizontal wells are configured in the same way as those in SAGD and a corresponding number of vertical wells are distributed around the horizontal wells. The upper horizontal well is used for steam injection and the lower one is used for water production and the surrounding vertical wells are used for oil production. During steam drive, low steam quality at the bottomhole due to high bottomhole pressure can lead to serious water production, which can be eliminated with this technique. The technique was tested in one well group in Block Wa59 which is a mid-deep extra and super heavy oil reservoir. The vertical gap between the paired horizontal wells is 20m, 50m between vertical wells and horizontal wells and 70m between the vertical wells. Some matching technological measures were provided, such as dual pipe steam injection pipestring for solving the uneven steam injection problem, deep pumping and high temperature large displacement lifting for eliminating pressure drop during fluid lifting, which ensured the results of gravity water drainage assisted steam flooding test. The test has resulted in obvious incremental oil production and water reduction with fluid production increased from 179t/d to 526t/d, oil production increased from 31.0t/d to 96.5t/d and watercut dropped from 91.1% to 84.69%. The technique has provided a new way for reservoirs not suitable for converting to steam flooding or SAGD development. It will be used widely in Liaohe Oilfield and other crude oil fields.

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