Combination Strategy of Wireline Logs and Annulus Connectivity Technologies, During Plug and Abandonment Operations of Inactive Old Wells, Supports Identification and Protection of Aquifers, Stablishes Effective Transverse Cement Barriers, and Preven

Abstract This paper presents the application of different technologies during the well plug and abandonment campaign of inactive old wells, where the lack of subsurface information jeopardizes the design of a proper abandonment that fulfills government regulations and industry standards, such as aquifer protection and placing effective well integrity barriers, to mitigate the risk of fluid migration from the wellbore to the environment, aligning our operations with some of the United Nations Sustainable Development Goals. Due to the lack of information on the +100-year-old wells, during the Plug and Abandonment (P&A) campaign, it was necessary to run different wireline logs to identify the presence of aquifers using pulsed neutron logs, along with verifying the cement behind the casing and validate casing corrosion. Once this information was acquired, most wells required cement placement behind casing using perforating or annulus connectivity technologies such as hydromechanical perforation blades, torch cutters and pressure cutters, to prevent affecting the integrity of the second casing. All those alternatives were validated by Technical Authorities according to the Well Intervention Guide (WIG) process. Taking advantage of the combination of different technologies, it was possible to successfully carry out the definitive plug and abandonment execution of more than 70 inactive old wells in several fields (Colorado, Buturama, Camoa, Petrolea) in Colombia where most of them exhibited integrity issues and sustained casing pressure. The presence and depths of aquifers were identified properly and protected according to government regulations, likewise, the integrity of the pre-existing casings and cement were verified. New effective transverse barriers that covered the annulus were established using annulus connectivity alternatives such as explosive-free torch cutters and hydromechanical perforating technologies among others, to communicate between casings and install effective transverse barriers without affecting the integrity of the external casing. With this strategy, it was possible to perform the Plug and Abandonment (P&A) operations applying the technology available with no HSE incidents and supporting Corporate Social Responsibility (CSR), aligned mainly with two of the United Nations Sustainable Development Goals, Clean Water and Sanitation, and Life on Land, among others. The Application of Pulsed Neutron-Neutron (PNN) Log is an option during Plug and Abandonment operations as an innovative solution when the identification of aquifers is required on inactive old wells with a lack of information. In order to establish effective transverse barriers, there are useful alternatives for annulus connectivity like explosive-free hydromechanical perforation and torch and pressure cutter technologies to prevent damage to the external casing when placing cement barriers in the annulus.