Desenvolvimento de uma metodologia para estimativa da pressão de poros durante a perfuração utilizando um modelo de previsão da taxa de penetração

Abstract

This work proposes a methodology to estimate pore pressure while drilling since its knowledge is essential to guarantee a safe and efficient drilling operation. For this purpose, we used the stochastic model proposed by Ohara that was designed to estimate the rate of penetration, from drilling parameters, as well as the compressive strain of the rock. This work proposes the construction of stochastic models to estimate the compressional travel time, while drilling, on the drill bit depth. These models are determined by dynamic linear regression, with constant models updating. These petrophysical variables are measured by 𝐿𝑊𝐷(logging while drilling) tools, such as Gamma Rays , Resistivity, Density, and true vertical depth, which assumes a possible physical association with argilosity, kind of fluids on the porous of the rock, porosity and compaction, respectively. Once the rock compressive strain is estimated, and the rate of penetration is instantaneously determined while drilling, the pore pressure is quantified through the Ohrara´s model updating. The results show better adjustments to the models for compressional travel time estimation which contains the variable density as one of the explanatory variables also better conformity to the statistical assumptions of regression. Consistent results for the pore pressure gradient for the Brazilian pre-salt area were obtained with values between 9.3 and 9.7 lb/gal, corresponding to values reported in the literature.