Oilwell Cement Pulsing to Maintain Hydrostatic Pressure—A Search for Design Model

Presented are theoretical and experimental results from a project supporting development of a new method for cement vibration in well’s annulus to prevent gas migration. In this method, cyclic pressure pulses are applied at the wellhead and transmitted down the annulus. These pulses cause reciprocation and shear within cement column—a process delaying the loss of hydrostatic pressure and preventing the inflow of gas into the well’s annulus. Field tests in real wells conducted to observe transmission of a single pressure pulse and to measure compressibility of setting cement showed that application of pressure pulses of 100 psi amplitude and 0.1 Hz frequency may be an effective and inexpensive way of preventing gas flow after cementing. The paper presents development of a cement pulsation design method based upon the analytical model of pressure propagation in Bingham plastic fluid and experimental data on rheology of cement slurries subjected to continuous shear. The primary objective of the method is to minimize the likelihood of gas invasion into the cement-filled annulus.