Temperature Anomalies in Wells Due to Cementing of Casing
Authors: Gretener P.E. 
Published: December 2007

Abstract
Temperature measurements were made in the surface portion of a test well drilled in Central Texas. The well portion of a test well drilled in Central Texas. The well was drilled to 304 ft by the cable tool method and surface casing was set and cemented. Temperature observations were made in the 25-hour interval between termination of drilling and installation of casing. Subsequently, temperature data were obtained, at progressively longer time intervals, to a total time of 280 hours after cementing of the surface casing when deepening of the hole by the rotary method commenced. Field observations indicated that a hole drilled by the cable tool method is heated (the maximum observed anomaly was about 5F); and hydra- tion of the cement leads to a general heating of the well.
A maximum temperature of about 15F was, observed 14 hours after cementing was complete.
Field measurements were supplemented by a laboratory study. Both the thickness of the cement annulus and the thermal diffusivity of the surrounding formation were varied. Results indicated that both parameters have a pronounced influence on the resulting temperature pronounced influence on the resulting temperature anomaly. Thus, an interpretation of the temperature log in terms of cement thickness behind the casing is permissible only when the lithology of the formation is reasonably uniform.

Introduction
The test well, Bill Stribling No. 3 (Fig. 1 ), is located in Central Texas over the Llano uplift where the sedimentary cover over the igneous basement is about 1,240 ft. The well was cable tooled to 304 ft between Sept. 22 and Oct. 27, 1964. The cable tool method was chosen since cavernous zones posed serious problems in a previous attempt with the rotary method (the bit dropped 6 ft previous attempt with the rotary method (the bit dropped 6 ft at one stage and circulation loss could not be controlled); 13-in. casing was set to 80 ft and 10-in. casing to 128 ft.. but neither casing was cemented. At noon on Oct. 27, drilling was suspended.

Instrumentation
All field measurements were taken with a 1,500-ft multiconductor rubber cable. Twelve glass bead thermistors are molded into the lower part of this cable at 25-ft intervals. Over the range of temperatures encountered in the shallow subsurface, these thermistors show a change of electrical resistance of about 100 ohm/ deg. F, Resistance for each thermistor is measured while the cable is at rest. Measurements are made with a four-digit bridge and an electronic direct-current null detector. Accuracy of the measurement is within 1/2 ohm. The cable resistance is measured separately for each cable position and subtracted from the reading. After the resistance of all thermistors has been determined, the cable is moved the desired distance-generally not less than 5 ft-and the next sequence of measurements is taken. Since the thermistors are insulated from the borehole fluid by about 0.1 in. of rubber, their time constant (95 percent recovery) is several minutes. Thus, a waiting period of 5 to 10 minutes is necessary before reliable measurements can be taken. As a result, each temperature log took about an hour to complete. This makes the tool ill-suited for the observation of transient temperature conditions as described in this article. A continuous logger such as the High Resolution Thermometer* or the one described by Simmons would be superior.

Field Measurements
Temperature measurements in the Stribling No. 3 well are summarized in Fig. 2.
JPT
P. 147