Elements Affecting Thickening Time of a Cement Blend

Abstract

Abstract This paper is a continued study of the work presented in SPE 13041, "Improved Bulk Blending presented in SPE 13041, "Improved Bulk Blending Techniques for Accurate and Uniform Cement Blends." Further investigation was conducted to better understand the factors which affect the physical performance of a cement blend, specifically the performance of a cement blend, specifically the thickening time. The variability of neat cement was found to be one of the main elements affecting the thickening time. Cement samples from one load of cement and samples from many different loads were seen to differ significantly in thickening time. It was determined that standard thickening time tests do not necessarily indicate the true responsiveness of a cement. Effects of sampling procedures on thickening times and additive distribution were investigated. Placement of sample valves was found to be an important factor affecting the sampling. Using proper sampling procedures and by conducting pilot tests with the same cement used to blend a pilot tests with the same cement used to blend a job, thickening times can be correlated between the laboratory and the field. The effects of offshore transportation and transfer of cement blends to the H g were also examined. The uniformity of the cement did not change with the transfer from the boat to the rig with hematite or retarding additives. Introduction Because cement slurry design has become so complex being able to deliver a slurry with the designed thickening tine has become more critical. It was noted that after assuring that the design was properly blended and the blend verified for additive properly blended and the blend verified for additive concentrations as described by Pace that in many cases the thickening times using samples blended in the lab (pilot blends) differed significantly from the times obtained from bulk house samples an samples. Research was started to determined these thickening times varied. The first and main element investigated was the neat cement. The neat cement was found to have varied responsiveness even in samples from one truckload of cement (50,000 lbs. or 22,675 kg.). During the course of the investigation it was noted that a group of cement samples will respond the same at low temperatures, but drastically different at high temperatures. It was found that the best correlation between pilot tests and field blends was accomplished when a pilot test was run immediately prior to blending with cement from the silo used for prior to blending with cement from the silo used for the field blend. Sampling procedures were also suited to determine their effects on the additive distribution and the thickening times. Placement of the sample valve played a critical role in obtaining representative samples. After determining the proper placement of the sample valve and using a proper placement of the sample valve and using a controlled amount of air pressure when sampling, the correlation between pilot blend thickening times and field blend thickening times was very good. The effects of transferring a cement blend from a boat at sea level to rig tanks about 100 ft (30 m) above sea level was investigated. Hematite blends and low quantity fluid loss and retarder additive blends were both studied during the transfer to the rig. It was observed that the uniformity of the cement blend did not change during the transfer from the boat to the rig. VARIABILITY OF NEAT CEMENT For years it has been known that cement varies from manufacturer to manufacturer. Service companies and oil companies know that when suppliers are changed the pilot testing for a job needs to be repeated. Laboratory cement samples are normally obtained from the cement supplier or from a company bulk facility.