Rapid Cement Quality Control Method For Improved Oilfield Cementing

Abstract

ABSTRACT A critical factor deter-mining the performance of the complex slurry formulations used in oilfield cementing is the variability in the properties of the cement. Conventional methods for cement analysis are expensive and time-consuming; they often focus on determining the hulk composition of cements rather than on the wider range of properties which affect cement performance. This paper describes u new, rapid and accurate cement quality control method, based on Fourier transform infrared (FTIR) spectroscopy, for determining the components of cements which are key to their performance. The FTIR spectrum, measured within a few minutes, is a unique "snapshot" signature of cement composition and particle size. The extent of cement "aging" is encoded in the measurement. Multivariate calibration models based on a large database of cements allow the spectrum to be transformed to a quantitative analysis of the clinker phases, the sulphate, hydroxide and carbonate minerals and minor oxides. The method can also be used for the quantitative analysis of cement blends, Example applications of the method to the diagnosis of problem field cements lead to a discussion of the effects of cement aging and contamination on slurry thickening properties. The use of the method at a field laboratory allows (i) rapid screening of cements and rejection of those which do not meet specifications, (ii) more efficient testing of slurry formulations prior to field use and (iii) rapid evaluation of local cement supplies in newly developed oilfields. Most importantly, the method can eliminate the use of cements which may cause major operational failures in the field. Thus, the method improves the overall efficiency of oilfield cementing operations. INTRODUCTION The efficiency of oilfield cementing operations depends on the performance of complex slurry formulations containing cement and several additives. The performance of a given formulation critically depends on the properties of the cement component. Cement variability increases the number of performance tests required to optimise a complex slurry formulation for field use. From time to time, unpredictable cements lead to expensive serious operational failures in the field. Rapid and accurate cement quality control methods are therefore urgently needed to screen oilwell cements and to identify cements which may produce an abnormal slurry performance. A recent paper [1] described the use of a cement characterisation program in a field laboratory to diagnose the performance of several cement slurry formulations. The paper briefly described the use of Fourier transform infrared (FTIR) spectroscopy as a qualitative tool for monitoring the batch to batch variability of cements. This paper describes an improved, rapid and accurate cement quality control method, based on FTIR spectroscopy, for the quantitative analysis of the components in cements which are key to their slurry performance. Applications of FTIR methods in cement chemistry extend to the direct prediction of slurry performance from FTIR spectra [2] and the in-situ monitoring of cement hydration reactions in the presence of various additives [3]. FTIR spectroscopy has been widely applied to the analysis of many complex materials [4, 5, 6].