Geochemical Techniques to Detect Sources of Fluids in Highly Pressured Casing-Casing Annuli CCA

Abstract

The buildup of high casing-casing annulus (CCA) pressure compromises the well integrity and can lead to serious incidents if left untreated. Potential sources of water causing the elevated CCA pressure are either trapped water in the cement column or water from a constant feeding source. This study utilizes inorganic geochemical techniques to determine the provenance of CCA produced water as trigger for high pressure in newly drilled wells. Affinities in the hydrochemical (major, minor and trace elements) and stable isotopic (δ2H, δ18O) composition are monitored to identify single fluid types, multi-component mixing and secondary fluid alteration processes. As a proof-of-concept, geochemical fingerprints of CCA produced water from three wells were correlated with potential source candidates, i.e., utilized drilling fluids (mud filtrate, supply water) from the target well site, Early - Late Cretaceous aquifers and Late Jurassic - Late Triassic formation waters from adjacent wells and fields. Geochemical affinities of CCA water with groundwater from an Early Cretaceous aquifer postulate the presence one single horizon for active water inflow. Non-reactive elements (Na, Cl) and environmental isotopes (δ2H, δ18O) were found to be most suited tools for fluid identification. 2H/1H and 18O/16O ratios of supply water and mud filtrate are close to global meteoric water composition, whereas formation waters are enriched in 18O. Elevated SO4 and K concentrations and extreme alkaline conditions for CCA water indicates the occurrence of minor secondary alteration processes, such the contact of inflowing groundwater with cement or fluid mixing with minor portions of KCl additives. The presented technology in this study enables the detection of high CCA pressure and fluid leakages sources, thereby allowing workover engineers to plan for potential remedial actions prior to moving the rig to the affected well; hence significantly reducing operational costs. Appropriate remedial solutions can be prompted for safe well abandonment as well as to resume operation at the earliest time.