This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 199561, “Validation of Transient Annular Pressure Buildup (APB) Model Predictions With Field Measurements in an Offshore Well and Characterization of Uncertainty Bounds,” by Rahul Pai, Anamika Gupta, and Udaya B. Sathuvalli, Blade Energy Partners, et al., prepared for the 2020 IADC/SPE International Drilling Conference and Exhibition, Galveston, Texas, 3-5 March. The paper has not been peer reviewed.
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 buildup (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. The complete paper reports the results of a study that compares the temperature and pressure measurements from these wells with model predictions.
Introduction
Though APB has been studied by well designers for decades, the use of downhole measurements to study APB has been somewhat limited. Previous uses of downhole instrumentation to study APB phenomena principally have centered on monitoring the magnitude of the APB and managing the risk. None, as far as the authors are aware, use the results gathered from downhole measurements to verify the results of the models that routinely are used in the design of the wellbore tubulars and APB-mitigation technologies.
Notwithstanding the wealth of literature on the subject of APB, several crucial and fundamental questions remain unanswered. Chief among these are:
What is the accuracy of thermal-model temperature predictions during various well operations?
How do temperature uncertainties influence APB predictions?
When APB magnitudes are large enough to require installation of APB mitigation devices?
How do the mitigation devices perform over the life of the well?
The complete paper seeks to address these questions through an examination of downhole pressure and temperature measurements and a parallel analysis of model predictions. Furthermore, field data and model predictions are juxtaposed, sources of uncertainties in the measurement data and model inputs are considered, and overall uncertainties in the APB predictions (i.e., model estimates) are characterized.
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