Thermal Stresses Analysis of Casing String used in the Geothermal Well Completion Design of the X Field, Indonesia Kris Pudyastuti,, Nanda Pratama Yufi, Maman Djumantara, Abdul Hamid, Afiat Anugrahadi
Petroleum Engineering Department, Trisakti University, Jakarta
Abstract
By any change in temperature to a material, a thermal stress is created. Temperatures rise in geothermal well bore not only causes the decrease of casing materials yield strength, but also leads to the change of casing materials elastic modulus and coefficient of thermal expansion. Casing materials modulus of elasticity decreases linearly with the rise of temperature, while its thermal expansion coefficient increases with the rise of temperature. So, in the casing strength design, it is necessary to consider the influence of temperature variation on the above parameters. This study explains the thermal stress that occurs in the casing material, involve high temperature of wellbore about 200-300 oC, heat transferred from rock formation. The temperature changes between rock formation or reservoir and casing, cause the casing to expand and shrink, and ultimately failure at a certain temperature conditions point. This failure will change the production casing in length, as well as the well integrity. So, the casing design in geothermal must consider high temperature first, because the thermal effect on the casing affect in strength and resistance and burst, that cause the maximum joint strength of the casing decreases, and leads to the collapse of the well. This study gives a benefit, i.e. recommendation of the casing design for the field, which has similar characteristics with the X Field – Indonesia. However, the knowledge of overburden and fracture pressure gradients, is a determinant of the depth of the casing shoe, must be a major concern. Reservoir geomechanics studies will provide more accurate information about overburden and fracture gradients.
Keywords: high temperature difference, thermal stress, plastic deformation, geothermal well, reservoir geomechanics
