Validation of Transient Annular Pressure Build-Up APB Model Predictions with Field Measurements in an Offshore Well and Characterization of Uncertainty Bounds

Abstract

Abstract The average geothermal gradient in the subject deepwater field in Nigeria is 4.37 °C/100 m, nearly twice the gradient in most fields. As a result, the magnitude of the expected annular pressure build-up (APB) during steady state production is large enough to threaten well integrity. Therefore, an insulating packer fluid (IPF) was used in Annulus A to reduce heat transfer to the outer annuli and to regulate the APB within acceptable values. To gain confidence in the thermal analyses and to estimate the efficacy of the IPF, downhole temperature and pressure sensors were installed in the completion string and in the Christmas Tree of selected wells. Measurements during flow tests on these wells were thereby obtained. Our paper reports the results of a study that compares the temperature and pressure measurements from these wells with model predictions. Specifically, we compare APB predictions with field measurements and determine the validity of the thermal model and rheological models of the IPF fluid used in the thermal model. We also characterize the uncertainty inherent in predictions of wellbore temperatures. There are few published downhole annular P-T measurements. Therefore, the reliability (and post-installation performance) of APB mitigation devices is often difficult to assess. This project to obtain measurements of downhole APB under controlled conditions is an important step in the calibration of currently used APB models, and in the establishment of guidelines for "robust" well design(s) in the face of APB loads and lifetime well integrity concerns.