Research on the Modified Model for Steady Displacement Interface Shape in Inclined Wells with Eccentric Annuli

ABSTRACT

It is well known that a displacement interface reflects the intermixing extent of two-phase fluids. Optimization of displacing and fluids’ property parameters is the key to achieve good cementing quality according to the displacement interface shape. In previous literatures, the model for the steady displacement interface shape in inclined wells only takes the factor of annular azimuthal angle into account, but not including annular radium term, which is imperfect. In this paper, by comprehensively analyzing the effects of both azimuthal angle and annular radium on the displacement interface shape, we establish a modified model for the steady displacement interface shape in inclined wells with eccentric annuli on the basis of a 2D Hele-Shaw displacement model, which will be more suitable for describing the actual displacement interface shape. From the modified model, we obtain: When density difference is smaller, the position of interface front is on the external casing wall of the annular wide side; otherwise, it will occur on the wellbore wall of the annular narrow side under a greater density difference. The displacement interface length in inclined wells with eccentric annuli is decreased and then increased with the increase of density difference, which indicates that there does exist an optimal density difference to make the interface length minimum. For a certain casing’s eccentricity, the optimal density difference in inclined wells is gradually decreased with deviation angle. When meeting the conditions of pressure stability and anti-leak, a greater density difference can obtain better displacement effect for vertical wells, otherwise, a smaller density difference can be good for horizontal wells.

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