Oil Reservoir Sandstone Evaluation with Digital Backscattered Electron Images

Abstract

ABS1RACfMineralogical and pore characterization has become an important key when evaluating oil reservoir quality. Presence of diagenetic or secondary mineral such as clays and cementing material can modify rock's texture, affecting in many cases the porosity and permeability during production and EOR processes.Scanning electron microscopy (SEM) and other related techniques have been widely used in petroleum industry to study and characterize sedimentary rocks.Backscattered electron (BSE) detectors and X-ray analysers are tools generally associated with SEM instruments, used by petrographers and petrophysicists who have taken a deeper concern with rock porous media (texture and mineralogy) through micrographies (analog signal) and its processing (digital signal). Relation between mineral composition and gray tone in the original signal, results on what could be called BSE imaging technique which shows some advantages over conventional techniques.Core samples from Venezuela western region have been evaluated by BSEI. Micrographies from a SEM, working in the BSE mode were digitized and processed whith PDIFRAC software which was developed for this purpose.References and illustrations at end of paper 153 Mineral and porosity fractions of the cores are presented for different depths. These results are compared with results obtained previously by XRD, IR and thin section petrography on the same samples.Images are used to provide mineralogical composition, porosity maps, fractal dimention calculations and to visualize potential cases of formation damage by fines migration (kaolinite and pyrite fines) IN1RODUCfIONSedimentary rock characterization is an important step in activities such as exploration, drilling, stimulation and enhanced oil recovery, mainly because the nature of that kind of rock (geometry and mineralogy) will define the specific treatment to be given to the reservoir 1.The aim of this work is to show preliminary results of a proposed technique for sedimentary rock characterization, based upon the analysis of digitized images obtained by scanning electron microscopy (SEM) in the backscattered electron mode.Conventional SEMs bring the options of X-ray analyzers and backscattered electron detectors (BSE). The first give chemical information as elemental composition in a mineral and the former gives mineral phase information directly due to the relation between intensity of the signal output and average atomic number in a mineral, consequently different minerals have different gray tone images 2 Oil Reservoir Sandstones Evaluation with Digital Backscattered Electron I Images SPE 23667 on the microscope· CI'R. At this point image analysis plays a fundamental roll.Mineralogy is a parameter that can be determined by other techniques such as thin section petrography, infrared absortion and X-ray difraction. Somehow this techniques give a limited information about the atributes of the porous space (geometry, grain size distribution) and as in the case of thin section petrography a subjective approach is given.Hav...