Real-Time Measurement of Downhole Annular Cementing Temperature for Precise Cementing Design and Application

Abstract

Abstract The tests required to customize a cement system for a well are run either at Bottom Hole Static Temperature (BHST) or at a lesser temperature known as Bottom Hole Circulating Temperature (BHCT), depending on the specific test being run. Many of the characteristics being optimized in a cement system must be tested as closely as possible to the actual temperature encountered by the cement slurry as it is circulated into a well. Failure to test the system at the correct temperature can result in improper loading of expensive additives, and expensive cementing failures. Many in the industry have long realized that standardized API tables will not always give the most accurate representation of BHCT for every well. In order to most accurately design a cement system, it is necessary to have a better understanding of the actual temperature encountered by the system during placement in a given well. Accordingly, computer models have been developed to simulate conditions encountered down hole. Having worked with such programs, the authors believe that in order to be accurate, most of these models require lithological thermal conductivity, and fluid specific heat data that is not generally available on most new wells. Because of these requirements, many simulations are run where "default" or "average" input values are used, and the Circulating Temperature projections become highly educated guesses. In an effort to procure more accurate and useful data, technology has been developed that allows for the monitoring of annular temperature of all fluids during placement of cement in a new well. Further, the technology allows for continued monitoring of the cement temperature during the critical cement transitory hydration phase, as well as throughout the life of the well. The authors will detail the development of the technology and the actual application in the field in multiple countries. Data obtained from wells utilizing the technology is analyzed and compared to current API values as well as BHCT projections from a Finite Analysis computer model. Finally, the authors will detail how the information made available by this technology can be applied to provide more accurate, fit for purpose cement designs that are optimized for the actual conditions encountered in a well. Introduction In a review of the available literature on the subject of downhole circulating temperature, the authors found that several of the wells detailed in previous works were not exactly configured as would be the case in an actual casing cement job. In many of the wells examined, the temperature recording devices were placed down hole in the drill pipe, or inside the casing1,2, and temperatures were recorded on various media while the well was circulated with the BHA off bottom. The fact that fluid velocity both inside the drill pipe and also outside the drill pipe would be significantly different than when the much larger casing was in the hole did not go unnoticed by the authors. Honore1 observed that "the circulating temperatures recorded while circulating on bottom with drill pipe in the hole may not be representative of the actual circulating temperatures on bottom when cementing". Others reported data collected with casing in the well, but with the sensors mounted inside the casing, and only collected data while circulating with mud3. The authors were also aware of some downhole devices whose electronics generated enough internal heat to make their recorded temperatures somewhat questionable2. There is also the issue of different fluids having different heat carrying capacities, and the possibility that the multiple fluids pumped on a cement job might impact circulating temperatures differently than a well only circulated with mud.