Integrated Laboratory Research Procedure for Core Cavernous Samples

Abstract

Evaluation of storage capacities with a separate evaluation of vuggy components of porous-vuggy reservoir rocks is quite complicated with the use of conventional logging methods. The use of nuclear-magnetic logging (NML) makes it possible to increase the reliability of evaluation of storage capacities of such reservoirs, but to adjust algorithms for NML interpretation, it is required to perform petrophysical study of core, which in turn are complex for practical implementation under the laboratory conditions. The solution of this issue requires an integrated approach and leads to development of integrated methodology of core studies. Two methods are used as a basis: X-ray computed tomography (X-ray CT) and laboratory nuclear magnetic resonance studies (NMR). At the first stage of the research, X-ray CT method is used to determine the cavernosity in the available whole core, on which the targeted zones are identified, and then whole core samples (100mm) are prepared. After that 100mm samples are extracted, conventionally tested to determine gas and liquid porosity, reextracted, and then samples of 50mm in diameter are drilled out to be compatible for testing in NMR-spectrometer (relaxometer). 50mm samples are restudied with the use of X-ray CT method to determine gas and liquid porosity at saturation with formation water or kerosene, after which a complex of studies is performed in NMR-spectrometer (relaxometer) to determine the total porosity by using NMR method, to identify cavernous porosity and to specify transverse relaxation time boundaries for caverns, T2cav. cutoff which are the values separating the cavernous porosity from the matrix porosity obtained by NMR curves of transverse relaxation time distribution T2. Ultimately, the methodology is based on the knowledge of cavernous porosity value, obtained by X-ray CT method on NMR curves, as a result of which it is possible to determine the value T2cav. cutoff, which can be used for determination of cavernous porosity on NMR curves. Additional methods of petrophysical studies (extraction, gas and liquid porosity) are required to obtain additional reference data on the properties of studied core samples. The distinctive feature of this work is the study of the method combining laboratory X-ray CT and NMR, to examine oversized cavernous core samples of 50mm with the suggestion to use method based on the developed design for retention liquid in the caverns during the laboratory NMR studies, on which application for a patent was made (invention). Conclusions on the good potential of the suggested methodology were made; a list of practical remarks for further works and improvement of suggested method of laboratory studies was prepared and includes the following: design modification, account of "undesired" components in the NMR results, optimization of studies consequences.