Study on Annular Pressure Buildup Occurring in the Production String in Dual Packer Completion Offshore Heavy Oil Wells

With the continuous development of unconventional resources, offshore heavy oil has attracted wide international attention. Heat fluid huff and puff and dual packer completion technology are often used in offshore heavy oil production. However, the annular pressure buildup caused by heat transfer and fluid expansion in the production has become a serious problem. It has brought a great threat to safe production of heavy oil. In this paper, regarding the dual packer completion and N2 injection, the temperature field in the production string is analyzed based on the heat transfer theory and energy conservation. The prediction method of APB is proposed considering the influence of the axial force and the cemented casing on the annular volume. At last, the mechanical strengths of the tubing and casing strings are evaluated. Analysis results indicate APB in C-annular is higher than that in the other annuli. The bottom of the un-cemented section of each string is most likely to be of failure. With the increase of N2 injection, APB decreases at a declining rate. The comparisons between the calculated value of APB by the proposed method and the measured data show high consistency with prediction errors less than 10%. The model developed in this paper is of referential value for annular pressure buildup mitigation and optimizing cementing operation.