Expansive and Shrinkage Characteristics Of Cements Under Actual Well Conditions

Abstract

The expansive and shrinkage characteristics of oilwell cements under actual well conditions of temperature and pressure have been measured by a highly sensitive device especially developed for the purpose. In tests using the device it was learned that some cements may experience an initial shrinkage during the first few hours after the cement has set. Introduction Because of the desire to achieve better well completions, the expanding characteristics of oilwell cements have been a subject of interest to the industry for a number of years. Studies have been undertaken to analyze the expanding properties of cements. The work done on oilwell cements presented data on expansion; however, for several reasons the testing methods that were used did not simulate well conditions. Following are some of those reasons: Reference measurements were started 8, 12, or 24 hours after the slurry was mixed. As a result, the most chemically reactive stage of cement setting was missed. During these first few hours, many well completion operations are being conducted and the cement's performance is very important. Cement samples were cured in confined molds under temperature and pressures that were not always representative of well conditions, and the samples were removed from the curing molds to make test measurements. The test specimens had to be removed from the curing environment before test measurements were made; they were transferred in and out of the curing environment during the entire test period. Curing temperatures and pressures were not, in most cases, representative of conditions encountered in wells. Many of the data were developed at atmospheric pressure and room temperature. Following are guidelines that we feel are essential in developing reliable, reproducible data that could be used to evaluate accurately the expansive characteristics of cement systems used in oil wells. Monitoring of the expansion and shrinkage of cements must begin as soon as possible and must not be interrupted during the entire test period. The test must be conducted at temperatures and pressures as close as possible to those encountered in wells. High-precision apparatus and accurate methods must be used to record continuously the expansion and shrinkage behavior of cements. The behavior of cements must be carefully monitored during the first 24 hours after the cement has been mixed and the test bas been started. This paper deals with the development of a device to meet the above requirements. It also presents preliminary test results. This initial testing indicated preliminary test results. This initial testing indicated that (1) temperature and pressure decreased the expanding tendency of the cements tested; (2) some cements show an initial shrinkage at high curing temperatures and pressures; and (3) commercial expanding cement expanded significantly at high temperature and pressure; no initial shrinkage was observed. Description of the Expansion Meter A diagram of the apparatus is shown in Fig. 1. The Expansion of Meter consists of the following:1. A metal frame that attaches to the base of thelid of a "curing chamber." JPT P. 905