1H spin-lattice relaxation time (T1) of kerogen as measured by NMR gives a regular increase with increasing burial depth. Organic maturation proceeds with a doubling of reaction rate for each 10°C increase in temperature. Relations between T1 and paleotemperature on the kerogen samples separated from argillaceous rocks of the MITI-Hamayuchi borehole were figured in due consideration of time. Paleogeothermal gradients on five boreholes and two outcropping section samples were estimated on the basis of the comparison with the standard figure of MITI-Hamayuchi. The gradient data obtained in this method show a slightly lower value than those calculated without any consideration of the absolute geologic age of kerogens. This evidence can be explained by slower sedimentation rate of all the sampling localities than in the MITI-Hamayuchi.
The Kazusa formations in Minami Kanto gas field consist of sandstones and siltstones alternately. The fluids flow mechanism in this reservoir is similar to that in naturally fractured reservoirs. A three-dimensional, two-phases double porosity model is applied for predicting the behavior of fluids in the sand/silt system. Using this model, we make simulation studies and verify theoretically the mechanism of fluids flow in the Mobara type gas field. As a result of simulation studies, original gas in siltstones is larger than that in sandstones and gas saturation in siltsones sways production performance together with permeability of siltstones.