Well integrity evaluation using acoustic and electromagnetic measurements

Abstract

The evaluation of downhole well integrity is an important business for the oil and gas industry. It is driven primarily by the need to optimize production while maintaining a safe environment despite the inexorable corrosion of casing strings and other harsh downhole conditions. Furthermore, with aging infrastructure, evaluating well integrity to plan plug and abandonment or slot recovery projects is critically important. Many technologies have been developed to address the challenges of evaluating casing and cement integrity under varied downhole conditions. These technologies are necessarily growing increasingly more sophisticated to meet the requirements of evaluating multiple cemented casing strings. In particular, wireline cased-hole logging techniques based on electromagnetic (EM) and acoustic techniques have been applied to casing corrosion and cement integrity evaluation. The acoustic measurement techniques deployed for well integrity evaluation typically include the sonic frequency range of tens of kilohertz up to the ultrasonic frequency range of megahertz. The frequency ranges are appropriate for characteristic resolutions of decimeters down to millimeters for sonic and ultrasonic measurements, respectively. These techniques are sensitive to the elastic properties of materials in the well completion and crucial for assessing zonal isolation. In the domain of evaluating corrosion in one or multiple casing strings, the traditional measurement approach uses EM techniques, which are sensitive to the metal thickness, the electrical conductivity (the inverse of electrical resistivity), and the magnetic permeability of ferromagnetic pipes. The spectrum of common EM casing inspection techniques encompasses a frequency range between quasi-static (direct current) up to about 100 kHz. More recently, transient EM or pulsed-field eddy current tools have been introduced. Specific physics and challenges associated with well integrity measurements must be understood and considered in existing and emerging technology solutions.