No abstract

The paper proposes a new approach for using a combination of radioactivity logging (neutron and density logging), which allows determining a set of gas reservoir parameters (nature of saturation, true porosity, gas saturation) taking into account influence of the pressure and temperature conditions of occurrence. Analysis of the ways of averaging the neutron-apparent porosity and the density-apparent porosity for obtaining the true porosity was made. Method of determination of gas saturation, which uses the same combination of radioactivity logging as in determining the true porosity of gas reservoirs, was developed. The results presented in the paper, were obtained over a wide interval of depth (up to 10 km). Application of developed approaches for determination of petrophysical parameters of gas reservoirs is demonstrated by the example of cased coalbed methane well.

To ensure the reliability and long-term usage of high housing buildings, important industrial, infrastructural and other objects, it is necessary to carry out engineering geological investigations of grounds (near-surface rocks) as the basis of these structures. To prevent the potential danger of destruction of the objects, it is also necessary to perform microseismic investigations of the near-surface geological environment and to agree the obtained results with the engineering geological parameters in the section of the test boreholes. Engineering geological parameters, determined by geophysical methods, are named engineering geophysical parameters. To solve the geophysical engineering problems, including seismic microzonation, at the Institute of Geophysics of the National Academy of Sciences of Ukraine a modern investigation technology has been created. The technology is based on apparatus and methodical complex of radioactive logging, which involves gamma-ray logging (GL), density logging (DL) and neutron logging (NL). This paper presents the results of developing adequate methodical and metrological assurance of the radioactive logging complex as a key technology element. Complexation of methods GL, DL and NL (taking into account a priori data) and the use of the proposed approaches allow determining a wide set of engineering geophysical parameters: density, porosity, volume moisture, groundwater level, the content of shale, the content of clay minerals, water saturation, dry ground density, etc. The features of obtaining parameters by the radioactive logging complex in the zone of aeration and the zone of saturation are shown, as well as taking into account the influence of the shaliness on the determined parameters. The effectiveness of the technology has been demonstrated by specific examples and confirmed by independent laboratory measurements.

The paper suggests methods for determining the basic parameters of ordinary and unconventional gas reservoirs, namely identification parameter, true porosity, gas saturation and volume gas content. The set of these parameters can be obtained in both open wells and cased wells with the help of a combination of density and neutron loggings taking into account PT-conditions of gas reservoirs occurrence (up to 10 km). The application of developed approaches for the estimation of the petrophysical parameters of gas reservoirs are demonstrated by the example of cased gas well.

The results of the creation of full-scale physical models of rocks for the calibration of combined tools of radioactive logging, which include density logging, are presented. Four sets of models were built for different logging problems. 1. Models of porous carbonate reservoirs with borehole (diameter 216 mm), equipped with interchangeable simulators of casing columns (146 mm і 168 mm) with cement sheath and tubing. The models are aimed to calibrate wireline logging tools for investigating the section of uncased and cased oil&gas wells. 2. Models of rocks of different density with borehole (160 mm), equipped with interchangeable drill collars (120 mm, 108 mm, 89 mm). The models are designed to calibrate density tools for logging while drilling horizontal oil&gas wells. 3. Universal models of porous carbonate reservoirs, crossed by holes of three diameters (200 mm, 160 mm, 125 mm). The purpose of the models is to calibrate wireline logging tools for investigation of section of uncased and cased oil&gas wells and tools for logging while drilling horizontal oil&gas wells. 4. Models of near-surface rocks of different density, equipped with a steel pipe (diameter of 51 mm) closely fitting to rock. The purpose of the models is to calibrate density tools for investigation of near-surface rocks when solving engineering-geological, seismic microzoning, ecological, etc problems. Physical models were designed and constructed by the employees of the Institute of Geophysics of the National Academy of Sciences of Ukraine together with partner organizations. The regular use of the models is due to the active work carried out by the Institute of Geophysics, together with partners, to create apparatus-methodical complexes of radioactive logging, which include the density logging. Graduation relationships and calibration functions for new density logging tools, obtained on the constructed physical models, as well as examples of density determination in different well conditions when solving research-and-production problems, are given.