This study aims to evaluate how the operational procedure adopted for the pellets placement and the exposure to subsurface conditions influences the mechanical integrity of bentonite plugs used as barrier elements in the abandonment of petroleum wells. To this end, two methodologies were used to obtain the plugs: from the first methodology, the pellets were immersed in diesel or olefin, which are proposed as displacement fluids in offshore operations, and then, hydrated in deionized water; in the second methodology, representative of onshore operations, the pellets were directly hydrated in deionized water. After that, the plugs were tested by compression and adhesion tests. These mechanical tests were also carried out for test specimens obtained from plugs exposed to four formulations of synthetic formation waters. The results obtained demonstrated that the previous contact with olefin adversely affects the mechanical stability of bentonite plugs, while plugs formed from pellets immersed in diesel presented satisfactory mechanical properties. The mechanical properties of onshore plugs attested the highly successful performance of these elements, once its compressive strength was minimally impacted by exposure to formation waters and more pronounced reductions were observed only in the adhesion properties after the contact with higher salinity formation waters.

One of the operational challenges for the use of bentonite pellets as a sealing material in the abandonment of offshore fields consists in their disposition inside the well. This study aims to analyze the interaction of fluid media, consisting of saline solutions (NaCl, CaCl2 and KCl) and organic compounds (diesel, glycerin and olefin), with bentonite pellets, aiming its application as displacement fluid in offshore oil well abandonment operations. The physical integrity of the bentonite pellets in contact with the fluids was verified through visual inspections and dispersibility tests. Linear swelling tests were also performed to evaluate the potential for swelling of pellets in deionized water after contact with the fluid media. The results indicated that NaCl, CaCl2 and KCl solutions completely compromise the physical integrity of the pellets, while diesel and olefin showed the best responses regarding the structural preservation. Futhermore, the linear swelling tests showed that, even after the contact with diesel and olefin for 1 hour, bentonite pellets have reached a total swelling in water of 78%, after 24 hours. In this way, diesel and olefin proved to be highly promising alternatives to be used as displacement fluids for bentonite pellets in wells to be abandoned in a submarine environment.