Annular Pressure and Temperature Measurements Diagnose Cementing Operations

Pressure and temperature measurements were made in the annulus of wells with sensors placed on the casings as they were run into the wells. The primary purpose of these measurements was to study the phenomenon of pressure reduction in the cement as it cures. Other phenomena were observed during these measurements, however, which are important to the cementing of a well and to casing design. This paper discusses three such phenomena: temperature in the annulus during cementing, loss of returns during cementing, and long-term pressure decline in a mud column above cement. The phenomenon of loss of returns during cementing can be very complex. Pressures in the cement during pumping may be greater than expected because the cement is rising higher than anticipated (because of by-passing of mud) or for other reasons. The resistance of the wellbore to hydraulic fracturing and consequent loss of returns is difficult to predict accurately. The behavior in two wells is described. Casing design requires assumptions about the pressure behind the casing to calculate internal burst pressure. The data available from two wells indicate that hydrostatic pressure exerted by mud left in the annulus above cement decreases with time, and original mud weights should notmore » be used for estimating burst pressure in casing design.« less