Using the new FRAC4Well Models for Predicting Fracture Gradient in Depleted Formations; a Key Driver for Borehole Stability Management in Brown Fields

Abstract

Optimal and consistent prediction of fracture gradient and stress path in depleted formation are of vital importance for well design and well integrity management. A modified and innovative concept for predicting stress path and fracture gradient for depleted intervals was formulated to ease well design and delivery in mostly conventional brown fields. It is imperative to further constrain the impact of poisons ratio as the major rock property affecting the stress path and fracture gradient evaluation considering the uniaxial scaling and variation of horizontal stresses generated by the strength interface of the drained poisons ratio scales in depleted formations. However, in addition to the modeling strategy, a rock property base stress path models (FRAC4Well model) was developed to account for the lateral stress variations at depletions for the change in minimum horizontal stress to pore pressure changes (pore-stress coupling). However, the study also considered the modeling strategy referencing linear elastic – constrained stress changes at different late time production periods within the reservoir, and the representative fracture gradient window. A stepwise validation strategy was formulated for stress arching hysteresis and it impact on thin/soft and thick/hard formations considering the sideburden and overburden impact for the different layers of the reservoirs as the horizontal stresses varies. A fast running semi-analytical model was also proposed to predict fracture sealing potentials after plugging and LCM selection during stress caging as a basis for fracture aperture closure mechanism. However, it is very important to have an accurate prediction of the boundaries of fracture gradients as the pore pressure depletes for optimal wellbore stability prediction to further mitigate challenges such as well control perturbations, borehole instability related NPT's and well integrity challenges that may arise as a result of erroneous fracture gradients predictions due to pore pressure depletion.