Modeling strategies on the geological formation for APB calculus in oil wells

Resumo

The thermal gradient imposed on oil wells along its life cycle can cause pressure variations in the

annular spaces, a phenomenon called Annular Pressure Build-up (APB). This subject is relevant, given the fre-
quency of occurrences in offshore fields located in deep and ultra-deep areas, such as the Brazilian Pre-salt, whose

exploratory interest has grown, given its potential for oil and gas production. The accurate modeling of the APB
phenomenon can prevent damage to the casing and the cement sheath, which may even lead to loss of well integrity.
Among the several variables involved in the problem, considering the geological formation as rigid or deformable
directly influences the APB estimate. Thus, this work aims to evaluate the effect of the flexibility of the geological
formation in the APB calculation. Numerical simulations of the pressure increase are performed using a multilayer
one-dimensional axisymmetric thermomechanical model. The methodology adopted is based on four macro steps:
reproduction of the reference scenario to verify the implementation of the APB calculation; considering formation
with null stiffness, result analysis considering rigid formation; evaluation of results adopting a linear constitutive
equation for the rocks. For the reference scenario, it was observed that the value of the formation modulus of
elasticity modifies the APB level by up to 35%.