Research on the prediction model of annular pressure buildup in subsea wells

The temperature difference between hot flowing production (including petroleum & natural gas) and fluid in the sealed annuli leads to annular pressure buildup (APB). The pressure increase could be very high due to the low compressibility of the annulus fluid, thereby endangering the well integrity and casing safety, especially in the HPHT (high pressure high temperature) subsea wells. In this paper, a semi-steady state model is presented to predict APB; the model takes several crucial factors into account, such as the differences of annulus temperature with depths, heat transfer diverseness at various well sections, and the ratio change between isobaric thermal expansion and the isothermal compressibility. The results of the case study demonstrate that APB is directly influenced by production rate, well depth, and annular length. In these factors, APB is most sensitive to the production rate. The higher the production rate, the higher pressure increase in the annuli becomes. The model provides a practical APB prediction method that is beneficial to well integrity and casing safety during petroleum and natural gas production process.