Effect of commingled water injection on the drilling safety of adjustment well

Adjustment well is one important technology for stable production and enhanced oil recovery (EOR) of old oil fields, but long-term water injection disturbs the reservoir pressure, leading to frequent well kick and overflow during the drilling of adjustment well. In this paper, a certain oilfield in the area of Bohai Sea was taken as an example. After a reservoir model was established, the commingled water injection in two adjacent layers whose permeability is vertically contrast was simulated by means of the numerical simulation method and the variation laws of reservoir pressure over the time in the area of adjustment well in the process of water injection and injection suspension of water injection wells were analyzed. It is indicated that the important factor leading to various complex situations during the drilling of adjustment well is that commingled water injection in the reservoirs with permeability contrast always keeps the pressure difference between two layers, which will not disappear and is still high enough to lead to well kick in the process of drilling after the injection is suspended for a while. According to the research results, it is recommended to adopt the numerical simulation method to predict the pressure of the commingled water injection areas with permeability contrast between layers before the drilling of adjustment well. And in addition, the suggestions on injection suspension time of water injection well during the drilling of adjustment well and fine water injection are proposed so as to provide the reference for the safe drilling of adjustment wells in old water flooding oilfields.