A Study of a Low-Frequency Downhole Hydraulic Pulsing Cementing Device and Its Field Application

Abstract A down-hole pulsed pressure device to improve the quality of cement bonds during primary cementing has been developed. The prime purpose was to control gas and water channeling and enhance the cement slurry displacement efficiency, especially in holes with a small annular space, and in holes with large washed out spaces occupied by mud-cake and in gas wells that are susceptible to gas channeling. These problems are difficult to treat with chemical cement agents. It is shown that pulsing the curing cement can improve the cement slurry hydration, shortening the time between the initial and final cement gelation and abating the slurry weight loss effect. Our experiments show the pulsing frequency is best between 10–30 Hz and the pressure amplitude should be less than 5 MPa. The device is highly innovative, is easy to engage to the casing string (under the float collar) and has no effect on the casing design. It does not cause failure during cementing, and does not alter the traditional cementing technology. It has been applied to gas wells in several fields in Sichuan province in China. The pilot well had 11 gas layers and is 4180m (13,714 ft) in depth, and the hole was prone to lost circulation (1.09g/ cm3 mud) and cave in. The cemented well interval was drilled with a 152.4mm (6") bit and cased with a 127mm (5") liner. There are troublesome formations in the interval that caused difficulties in logging and while running the liner. The down-hole pulsing generator worked well with the 1.50g/cm3 cement slurry, but due to the complicated hole conditions the displacement was not finished when the liner became plugged with cement. But after drilling out the cement plug, the CBL and other logs showed the cement quality had been enhanced 50% compared to the offset wells. Then in application to another three wells we also achieved significantly improved cement bonds. So it has been verified that this device can significantly improve cementing, and is easy to apply in the field. We intend to continue to apply it to wells with troublesome formations and to all gas and oil wells with cementing problems.