Acoustic Wave Propagation In Bonded And Unbonded Oil Well Casing

Publication Rights Reserved Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and considered for publication in one of the two SPE magazines with the paper. Full scale model studies in free and clamped pipe have resulted in many observations concerning the character of acoustic wave propagation in water, casing, cement and formation. Primary interest is centered in the detection of a cement sheath wave velocity. From measurements made of acoustic velocity in cement it is evident that a considerable range in longitudinal wave propagation velocity exists during the curing time. At atmospheric pressure with neat A.P.I. cement tests show that the range is from 3000 to about 12,000 feet per second. Tests run show the possibilities of cement wave interference in analysis of acoustic wave propagation in a three phase system composed of casing, cement, and formation. The physics-chemical aspects of cement hydration and cure are related to changes in velocity and signal attenuation. Representative amplitude readings in three casing sizes are plotted and tabulated with respect to the loading factor imposed by nine cement sheaths ranging in thickness from .19 to 3.25 inches. From this data a plot of Amplitude versus Propagation Wave Time reveals the optimum length of amplitude build-up of the pipe wave. Differences are noted with change in casing size. The effects of centralization and decentralization of the acoustic assembly are shown to be critical elements in making velocity amplitude, or other measurements related to acoustic wave propagation within concentric cylindrical boundaries. Acoustic wave propagation photographs made during model studies are reproduced with similar photographs made at field wells for comparison of the effects discussed. Introduction From measurements made of acoustic velocity in concrete it is evident that a considerable range in wave propagation velocity exists during the curing time.