Numerical simulation of the effects of cement defects on flextural wave logging

Oil and gas industry experiences challenging and there is a particular need for better monitoring for well integrity for increased oil recovery and for avoiding serious environmental consequences. Cementing is an integral part of well construction. Cement provides the seal, protection and support for the casing to maintain the strong barriers that isolate the well. To achieve effective isolation, cement needs to fill the area around the pipe and produce a channel-free section over a length of the cement column suitable to isolate zones and prevent leakage into or out of a hydrocarbon productive zone. Quality of cement seal needs to be monitored and evaluated. To ensure that a proper cement annulus has been placed, ultrasonic logging tools are used to inspect the cement‐to‐casing bond and to detect channels where fluids can flow within the annulus and defects inside the cement annulus. The combination of ultrasonic leaky Lamb-wave technique and Pitch-Catch technique is a promising approach for cement bond evaluation [1, 2, 3]. The ultrasonic leaky Lamb-wave is also called flexural wave. The flexural wave attenuation can be calculated from the amplitudes of the first wave packet of two adjacent receivers. Based on the measured flexural wave attenuation and acoustic impedance, the solid, liquid, gas (SLG) state of material behind casing can be estimated. This interpretation method is based on the assumption that the medium behind casing is homogeneous. What happens if the medium behind casing is inhomogeneous, for example, there is a defect filled with water in the cement. This always happens in real situation. In this paper, we establish a 2D Finite Different (FD) model to numerically study the effects of defects (filled with water) in cement annulus on flexural wave attenuation. Different scenarios are simulated and the influence of the defect’s size and location inside the cement on the flexural wave attenuation is studied. The simulation results can be helpful for understanding and interpretation of logging data. References [1] S. Zeroug and B. Froelich, Ultrasonic leaky-lamb wave imaging through a highly contrasting layer, IEEE Symposium on Ultrasonics, 2003, vol. 1, 794-798. [2] R. van Kuijk, S. Zeroug, B. Froelich, M. Allouche, S. Bose, D. Miller, J.-L. Le Calvez, V. Schoepf and A. Pagnin, A novel ultrasonic cased-hole imager for enhanced cement evaluation, International Petroleum Technology Conference-SPE, 2005, 10546. [3] B. Froelich, Multimode evaluation of cement behind steel pipe, Acoustics 08 Paris, 2008, 5023-5028.