Abstract
The problem of wellbore stability in expansive formations has frustrated engineers of oil fields since the start of oil and gas well perforation. The stability of shales rich in clay are deeply affected by its complex physical and chemical interactions with drilling fluids. Thus, these rocks with a high content of clay have shown significant changes, such as swelling or expanding, when placed in contact with aqueous fluids due to the adsorption of polar molecules of water or hydrated ions dissolved in the medium. These changes may cause collapse of the rock during drilling with water-based drilling fluids. For a better understanding of the phenomenon of interaction between the rock and the drilling fluid, this study aims to analyze reactivity of shales from the Recôncavo Baiano through their characterization. For this, the shales were characterized by CEC, XRF, XRD and Foster swelling. The results indicated that the shales showed significant values of CEC, FRX composition close to that of smectite, and XRD pattern with characteristic peaks of smectite. Regarding to Foster swelling, the shale of higher CEC also presented the higher value of swelling, indicating that the CEC can be applied as a parameter indicative of the reactivity.
Keywords:
reactive formation; characterization; inhibited drilling fluids
