Strength varying laws of rock soaked with supercritical CO₂drilling fluid and the prediction of safe mud weight window

Abstract

Drilling with supercritical CO2 (SC‐CO2) is an important new technology in petroleum engineering. The technology has many unique advantages for increasing the penetration rate and reducing formation damage, but it is a disadvantage for the wellbore stability. Therefore, an experimental technique has been developed to determine the safe mud weight window for drilling with SC‐CO2. More specifically, a special experimental apparatus has been designed to mimic the in situ temperature and pressure conditions during drilling operations. Different experiments were conducted using core samples soaked in SC‐CO2 and water‐based and oil‐based drilling fluids, respectively. Once the experimental measurements regressed, an empirical correlation, including time, temperature and pressure factors, was obtained to describe the compressive strength of the SC‐CO2‐soaked core samples. Further modifications were then made to the formulations used to calculate the densities of the drilling fluids at the corresponding burst and collapse pressure, respectively. In addition, the effects of dynamic cohesion, internal friction angle, and tensile strength on the wellbore stability were determined. Compared to the conventional water‐based and oil‐based drilling fluids, the SC‐CO2 drilling fluid performs better with respect to wellbore stability and has a wider safe mud weight window. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.

The effect of thermal stresses on the relation between rock failure and temperature and pressure of supercritical carbon dioxide jet

“…This helps to reduce the pressure loss in liquids circulating in well‐drilling operations, reduce the pressure requirements on the pumps on the ground, and form high‐pressure jets for underbalanced drilling at the hole bottom . Compared to the conventional water‐based and oil‐based drilling fluids, the SC‐CO 2 drilling fluid performs better with respect to wellbore stability and has a wider safe mud weight window . In addition, CO 2 density is sensitive to the pressure change, and the SC‐CO 2 jet produces a large temperature reduction in CO 2 because of the density reduction in jet expansion .…”

“…6,7 Compared to the conventional water-based and oil-based drilling fluids, the SC-CO 2 drilling fluid performs better with respect to wellbore stability and has a wider safe mud weight window. 8 In addition, CO 2 density is sensitive to the pressure change, 9 and the SC-CO 2 jet produces a large temperature reduction in CO 2 because of the density reduction in jet expansion. 10,11 The SC-CO 2 jet technique is potentially a new type of rock-breaking method that effectively combines mechanical and thermal energies.…”