Importance of Thermal/Stress Loading Analysis for Tubulars in HPHT Wells

Abstract

The upstream oil and gas industry is experiencing increased interest in exploration and production from the more complex, hostile, and deeper geologic horizons that are classified as high-pressure, high-temperature (HPHT) reservoirs. Well completion planning and design is becoming increasingly more critical and challenging because of the uncertainty that typically is experienced from the high pressure and temperature changes that can occur in operational scenarios during the well's lifecycle. The cost of a typical tubing completion equipment usually represents 15 to 25% of overall well cost. High operating temperatures and pressures cause significant pipe movement and high axial loads at the packer and tubing during the well operation. For wells where design margins can be slim, a detailed and robust stress-loading analysis and the aid of modern thermal-and-stress- analysis software can balance tubular equipment design versus risk. This approach provides savings on tubular cost by optimizing the tubing design so that it meets the company's integrity standards without being overdesigned. This paper discusses an engineering design methodology that can be followed for tubular equipment sizing and selection for complex wells. A typical list of reservoir and well parameters that are required to set up the well model for the thermal and stress loading analysis is presented. Importance of estimated thermal simulation is highlighted for tubular selection and design. A full integrity analysis for well casing and tubing design integrity will be performed for a complex, deep-water, high-rate, HPHT example well. The analysis will cover various anticipated operating loads during the life of the well and will include the effects of stimulation, production, and EOR flooding. Results are presented showing changes in temperature and pressures during well operating scenarios and impact of temperature changes on tubulars stress loading. Sensitivity analysis is then performed with applied landing forces on the completion for further discussion on limitations on well operating conditions during well life cycle.