Key Factors That Affect Cementing Temperatures
Authors: Wedelich H. , Goodman M.A. 
Published: December 2007

Current API standards for cement thickening time tests of casing and liners correlate circulating temperature with two variables - well depth and geothermal gradient. It can be demonstrated that many other factors affect cementing temperatures. Among these are casing sizes, prior drilling history, circulation rates, mud and cement properties, and inlet temperatures.

A computer program is used to predict circulating temperatures of mud in drill pipe, slurry placement temperatures, and temperatures during wait on cement. Actual circulating temperature field data from a well used to develop the API standards is compared to model predictions. The model is then used to predict temperatures with typical variations of the different factors. The results not only show which factors cause the most difference in cementing temperatures, but also show the significance of these effects compared to the API standards.

Background

The importance of temperature for design of cement slurries has been described in previous papers. In particular, Shell and Tragesser show the effects of as little as 20 degrees on pump time, thickening time, and compressive strength. Accurate knowledge of downhole circulating temperatures is even more critical in liner operations because of the need for an adequate seal at the top and bottom of the liner [2].

Circulating temperature measurements for 5 wells were published in 1941 [4) and formed the basis for cementing test schedules until the mid 1970's. The early schedules assumed a 1.5deg.F per 100 ft gradient and correlated circulating temperature with depth.

During the 1970's, circulating temperature measurements were obtained in 78 wells. This formed the basis for the current API temperature schedules that correlate circulating temperature with two variables - depth and gradient [5). Figure 1 is a graph of the API circulating temperatures compared to some of the temperature measurements used to develop the schedules. The graph shows general agreement with the API correlation, although variations on the order of 20deg.F are not uncommon.

In a more recent study, Venditto and George compared the API schedules to circulating temperature measurements in 52 wells. Figure 2 compares those measurements with the API schedules. Sixty percent of the wells agree with the API schedules within 10deg.F. Thirteen percent of the wells are greater than 20deg.F different than API. Two of the wells are 40deg.F cooler than API, and one well is 60deg.F cooler than API.

The overall agreement with the API schedules supports the conclusion that depth and gradient are the two most important variables for correlating cementing temperatures. The combination of depth and gradient results in a bottomhole static temperature. The disagreement with the schedules for 13 percent of the wells indicates the need to consider other variables. This paper uses computer modeling techniques to identify variables other than depth and gradient that can account for these differences.

COMPUTER MODEL FEATURES

A number of papers describe calculation methods to predict circulating temperatures. The computer model used in this paper was originally developed in 1978 and has been continuously improved since that time. The formulation of the model is described briefly in these references and in detail in reference 18.

For accurate prediction of cementing temperatures, the following model features are needed. The model must predict transient temperatures. Downhole temperature during cementing are changing rapidly due to changing flow conditions.

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