Dual Energy Microtomography Applied to Oil and Gas Assessments

摘要

Dual energy X-ray Microtomography (DE-MicroCT) has proven to be a valuable method in oil and gas industry because it provides non-destructive investigation of the mineral composition of internal structures, characteristic of reservoir core materials. In order to distinguish among different rock materials, a dual energy scanning is carried out to determine both the density and effective atomic number of the minerals of interest. Accurate and reliable quantitative measurements can be achieved with an appropriate calibration within the range of measured attenuation values. However, image quality is the key of an accurate measurement and image signal to noise ratio (SNR), which is related to the ability to define the ratio of the signal intensity to the ambient noise level, is primary determinant. This study provides an investigation of the inner mineralogy phases and microstructural characteristics of a reservoir rock sample by DE-MicroCT. For that purpose a carbonate with different ranges of total porosity and consequently permeability was used. Image analysis process is crucial for an accurate differentiation between calcite (matrix density = 2.71 g/cm~3) and dolomite (matrix density = 2.87 g/cm~3) minerals because they are very similar, although the last mineral is denser than the first one. The results show that small differences are enough to obtain measurements of different mineral phases in Brazilian reservoir rock samples. The results also illustrate that important morphometric parameters to petrophysics investigation may be obtained in this approach.