A dual-frequency acoustic measurement method for detecting fluid-filled channels at two boundaries in cased holes

The recognition of fluid-filled channels in cased holes is significant for the safety production of oil and gas wells. The fluid-filled channel at the cement-formation boundary is more difficult to be detected than that at the casing-cement boundary. To solve the key technical problem, a dual-frequency acoustic measurement method is proposed to obtain the cementation state of the two interfaces at the same time. The related theory is that the casing wave amplitude from the low-frequency source is sensitive to the channel at both two boundaries, but that from the high-frequency source is only sensitive to the channel at the casing-cement boundary. Therefore, high amplitudes of the casing waves from both two sources represent a channel on the casing-cement boundary, high amplitude from the low-frequency source but low amplitude from the high-frequency source represent a channel on the cement-formation boundary, and low amplitudes from both two sources represent no channel.