ABSTRACT
Gas leakage through cement in the annular space around a cemented casing is still a serious problem, although new additives and methods have reduced the problem. The problem is related to migration through the cement matrix itself or to migration along the cement's Interfaces with the casing and the formation, caused by poor displacement of mud and/or loss of hydrostatic pressure within the cement slurry during curing.
One solution to this problem Is to transmit vibrations to the cement through the casing. The objective of vibration of oil well cement is to counteract the continuous reduction of hydrostatic pressure and to maintain low permeability during hydration of cement. The hydrostatic pressure within the slurry must be higher than the pressure within the gas bearing formation. Vibration tests in a two meter high cement column have resulted in guide lines as to what frequency, amplitude, vibration Intervals and duration should be selected to maintain column pressure. For similar vibration parameters it has also been investigated if the short (1 day) and long term (7 days) strength of the cement has been negatively influenced. Different methods for practical implementation of oil well vibrations have also been considered.
Through vibration of oil well cement, not only the cement will become more gas tight, but also the physical bond between cement/casing and the strength of the cement itself will be considerably improved.
