Experimental investigation of acoustic features associated with cement damages in double cased-wellbores

摘要

Ensuring the integrity of oil and gas cased-wellbores is of crucial importance to operators around the world to maintain safe production and environmental compliance. While sonic and ultrasonic measurements have been developed for evaluating the well integrity of single casing strings, there is currently a gap in characterizing the cement and annular fill behind two or more casing strings due to the lack of sensitivity of the ultrasonic tools and the complexity of the sonic response. This abstract describes an experimental study to characterize the sonic response and help fill this gap in conjunction with a theoretical modeling effort that is reported elsewhere ~(1-3). Scaled laboratory experiments are conducted to acquire reference data used to verify the modeling approach developed to predict the guided modal characteristics of axially-propagating waves in concentric and non-concentric cylindrical structures immersed in fluid. These structures simulate the geometries and environment encountered downhole when conducting acoustical measurements to evaluate the cementation of oil and gas cased wells. Typically, cement is expected to fill the annular space between the outer string and rock formation. Nevertheless, cement damages such as fluid channels, partial cement coverage, and weak bonding interfaces, which can compromise well safety as well as environmental compliance, inevitably occur due to the harsh downhole environment and downhole operations. Measurements are made in a dual-string steel pipe of quarter scale in an immersion tank or in a sandstone formation with concentric as well as a variety of eccentric configurations. A set of samples are prepared with the cement in annulus B (the space beyond the outer casing) with purposefully introduced fluid channels in a controlled manner. A comparison of the experimental and numerical results indicates features in the sonic response that are indicative of channels in annulus B as distinguished from eccentricity effe