MODELING OF RHEOLOGICAL PROPERTIES OF DRILLING FLUIDS FOR ULTRA HIGH PRESSURE / HIGH TEMPERATURE (HPHT) OIL AND GAS WELLS

Oriji, A. B.; Dosunmu, A. and Joel, O.F

Department of Petroleum and Gas Engineering

University of Port Harcourt, Nigeria

ABSTRACT

Determination of mud properties at ultra HPHT deep wells has been a challenge in the Oil and Gas industry. Conventional mud designs and test equipment fell short of addressing inherent problems associated with these types of wells. This paper presents a novel approach in determining and modeling rheological properties of mud under this ultra high temperature and high pressure regime. Water based mud was formulated with special additives to enhance stability under such elevated temperature and pressure. Tests were conducted at 450, 460, 470, 480, 490 and 500°F as well as pressure of 9500, 9600, 9700, 9800, 9900 and 10000 psi. Using test results indicated that rheological property is a function of temperature, pressure and also the interaction effect of temperature and pressure respectively. Model coefficients were obtained using multiple regression analysis in visual basic.dot net software. The models which predicted the rheological properties with respect to temperature and pressure were developed. Results calculated from the model equations showed a good agreement with experimental values with less than 1% deviation. This will help predict rheological properties and rank the best of the models at high temperature and pressure thereby saving time and rigour associated with actual laboratory tests. Also, the generated mathematical equations for apparent viscosity, plastic viscosity, and yield point and gel strength will provide proactive step for practical drilling experience and for well planning.

Keywords: Apparent Viscosity, Plastic Viscosity, Yield Point, Gel strength, Temperature and Pressure.