PETROPHYSICAL CHARACTERISTICS OF THE SHALE GAS FORMATIONS IN THE BALTIC BASIN, NORTHERN POLAND
Abstract
Results of laboratory experiments combined with well logging to get information on density and porosity together with mineral composition were the basis for shale gas rock model construction. Density – bulk, skeletal and grain determined from various laboratory experiments and porosity – total, effective/dynamic and from dual liquid immersion measurement, well correlating with TOC and volume of kerogen, showed the place of organic matter and gas in pore space and the skeleton of claystone-mudstone gas formations. Results of pyrolysis (Rock-Eval), i.e. TOC (Total Organic Carbon) used to determine the hydrocarbon generation potential of rocks were also considered together with element composition from chemical analyses and mineral composition from XRD measurements. SCAL analysis, NMR experiments, Pressure Decay Permeability measurements together with water immersion porosimetry (WIP) and adsorption/desorption of nitrogen vapors (77K) method were realized and the comprehensive interpretation of the outcomes was done. Absolute permeability, pore diameters size, total surface area from Hg porosimetry were compared with outcomes of nitrogen physical adsorption/desorption method. It enabled extension of pore diameter range into extremely small values. The nitrogen adsorption/desorption method also contributed to porosity values, adding notable volume of the smallest pores. The results from NMR experiments confirmed a complicated porous space structure and showed that total surface area from adsorption/desorption of nitrogen method together with pore space area from Hg porosimetry correlate well with the irreducible water saturation. Laboratory results were combined with well logs (GR) and results of the comprehensive interpretation (PHI) and volumes of mineral components, for instance illite/smectite and kerogen. GEM logging results were also used to improve volume of carbonates in shale gas rocks matrix and organic/inorganic coal. Identification of Fe element was useful in pyrite recognition. Another important factor was including the sedimentological macroscopic description of cores before cutting plugs and geological homogenization of samples and adopting the proper sequence of laboratory experiments to be sure that all properties were determined on the same part of the rock material.
