Technical evaluation of calcium sulphate α-hemihydrate in oilwell application: An alternative to reduce the environmental impacts of Portland cement

The oil industry has been drilling wells since the last century using Portland cement as a cementing basic material. There are several environmental impacts associated with the Portland cement production from the raw materials extraction to the macro impact generated by clinkerization such as the emission of greenhouse gases, mainly carbon dioxide (CO2), combined with huge energy consumption for its production. The study of cement slurries with other precursors types is extremely important in order to obtain a paste with the best properties which are aimed to reduce the negative effects on the environment. Calcium sulfate α-hemihydrate (α-HH) is a material that presents high ecological potential and can be considered a less aggressive agglomeration agent to the environment than Portland cement. The objective of the present work was to develop and analyze the behavior of slurry systems based on α-HH as a basic agglomeration agent for oil well cementing. For this study, slurries were prepared with different water/gypsum ratio (WGR) and submitted to different curing periods (24 h, 7 and 28 days) and temperatures (27, 38 and 60 °C). Then, the additives were added to the slurries using different concentrations of retarding admixture (sodium tetraborate), of superplasticizer (polycarboxylate) and antifoam agent (silicol), aiming to obtain the technological properties required by the oil industry. Such formulations were evaluated through rheology tests, compressive strength and thickening, and thermal characterization (TG/DTG), X-ray diffraction (XRD), X-ray fluorescence (XRF), Infrared region absorption spectroscopy (IR) and scanning electron microscopy (SEM) techniques were performed to characterize the α-HH and its additive formulations. The results showed that the α-HH system with 0.5 WGR showed the best results. The additives were used satisfactorily to enable optimizing the technological properties of the slurry. The α-HH slurry is applicable for cementing shallow oil wells (500 m) under mild temperature and pressure conditions.