Abstract
To enable efficient design of oilwell cements that can be placed with precision and that can withstand the harsh conditions often encountered downhole, it is important to understand how these materials are built up at smaller length scales. Since cement pores and grains can be of micro- or even nano-meter sizes, and since they are connected in space, detailed cement characterization requires advanced experimental techniques of good resolution that can provide three-dimensional (3D) information.
In the present paper we demonstrate how the nano- and micro-structure in the interior of set cement samples can be studied by using a Focused Ion Beam - Scanning Electron Microscope (FIB-SEM). This instrument performs nano-tomography, allowing small 3D cement volumes to be digitalized. In this way, chemical mapping of element distributions within the solid cement phases can be performed, and the 3D pore network can be reconstructed in great detail. This makes FIB-SEM an ideal experimental technique for investigating e.g. cement porosity, chemical attack on cements, cement-formation (de)bonding and structural or chemical effects of additives. The final output of FIB-SEM experiments, being digitalized microstructural features like grains or pores, can be used as input for numerical modeling schemes.
The FIB-SEM experiments presented in this paper demonstrate how this technique can reveal subtle microstructural differences in two Portland G cement samples mixed with water-to-cement ratios varying within the range that is typically used for well cementing. These distinctions are shown to be complementary to the larger-scale differences observed within the same samples when analyzing them with micro computed tomography (µ-CT). It is shown how the spatial extent of the internal pore network and the pore sizes are dependent on the water-to-cement ratio. We also show, through various mechanical testing procedures, how this multi-scale cement porosity affects the macroscopic properties of the material.
In the present paper we demonstrate how the nano- and micro-structure in the interior of set cement samples can be studied by using a Focused Ion Beam - Scanning Electron Microscope (FIB-SEM). This instrument performs nano-tomography, allowing small 3D cement volumes to be digitalized. In this way, chemical mapping of element distributions within the solid cement phases can be performed, and the 3D pore network can be reconstructed in great detail. This makes FIB-SEM an ideal experimental technique for investigating e.g. cement porosity, chemical attack on cements, cement-formation (de)bonding and structural or chemical effects of additives. The final output of FIB-SEM experiments, being digitalized microstructural features like grains or pores, can be used as input for numerical modeling schemes.
The FIB-SEM experiments presented in this paper demonstrate how this technique can reveal subtle microstructural differences in two Portland G cement samples mixed with water-to-cement ratios varying within the range that is typically used for well cementing. These distinctions are shown to be complementary to the larger-scale differences observed within the same samples when analyzing them with micro computed tomography (µ-CT). It is shown how the spatial extent of the internal pore network and the pore sizes are dependent on the water-to-cement ratio. We also show, through various mechanical testing procedures, how this multi-scale cement porosity affects the macroscopic properties of the material.