Density difference optimization of displacing fluids in eccentric annulus of horizontal wells

Slow-flow drilling fluid caused by fingering instability of displacement interface is the main factor to result in oil/gas/water channeling. The displacement interface in horizontal wells is affected by resistance effect in narrow and wide clearances caused by casing eccentricity and buoyancy effect caused by density difference. Besides, impacts of the two factors on displacement interface are opposite. Therefore, displacement interface stability can be enhanced by optimizing the density difference of displacing fluids based on casing eccentricity in horizontal wells. The change law of the displacement interface length with time is analyzed based on the advantages and disadvantage of the method of three-dimensional numerical simulation to realize the target of minimum displacement interface length and have the matching relationship between the optimal density difference and casing eccentricity. The conclusions are as follows: the growth rate of displacement interface length slows down with time increasing, but it is not obvious; the too large or small density difference will reduce the displacement interface stability in the eccentric annulus of horizontal wells. In order to achieve the shortest displacement interface length in cementing, reasonable density difference shall be chosen on the basis of casing eccentricity. The study results provides theoretical basis for the design of displacement parameters and cementing length in horizontal wells.