Keiji Kojima

An estimation of the intrinsic permeability of argillaceous rocks and the effects on long-term fluid migration

Abstract The effect of intrinsic permeability of argillaceous rocks on long-term petroleum migration is discussed from results of both laboratory experiments and numerical sensitivity studies. Results of our experimental studies on one-dimensional mechanical compaction of both muddy slurries and mudstones show that porosity(φ)-permeability(K) relationships are linear on double logarithmic scales, i.e. φ and K satisfy the relationship: K=K0(φ/φ0)a, where K0 is initial permeability, φ0 is initial porosity, and ‘a’ is a parameter depending on the samples used. Comparison with published φ-K relationships of mudstones indicates that the above mentioned relationship could be extrapolated to natural condition when φ>0.3. On the other hand, the relationship becomes deviated from measured data in the low porosity range. Considering the importance of φ-K relationships in φ<0.3 on the timing of expulsion of petroleum from source rocks, this paper discusses the way to find out an appropriate φ-K relationship through trial and error matching of results of basin simulation using different φ-K relationships with observed pore pressure and porosity data. We also present one case study using an imaginary siliciclastic sedimentary basin and discuss the potential of a numerical study to establish one of the appropriate relationships, showing how calculated results become varied by choosing different relationships.

Toward the practical three-dimensional basin simulation. An example of the offshore Niigata sedimentary basin.

A three-dimensional two-phase basin simulator, BASIN3D2P, was applied to the offshore Niigata basin to make it clear the problems of basin simulation studies for practical exploration activities.The studied area was about 40km×45km, and was divided into 1, 258 grids horizontally, while ten horizons were deposited sequentially during about 16 m.y. Input data sets for the calculation were prepared by using data from exploration wells, interpreted seismic reflection profiles, results of geochemical measurements, and so on.The result showed that three-dimensional evolution process of the basin through geological time scale could be simulated by BASIN3D2P, and by modifying heat flow history, relative permeability curves, amount of initial organic materials, and duration of the calculation, we could improve the fitting of the calculated results with the observation.We, lastly, discussed possible practical usage of three-dimensional basin simulation to the estimation of oil accumulation in peripheral structures of the developed/depleted oil fields.

Experimental study on self-healing of bentonite/sand mixtures and its impact on hydraulic permeability

The effects of gas permeation on the hydraulic permeability of bentonite/sand mixtures were studied experimentally by conducting permeability tests with various fluids and by microscopic observations. In these tests, hydraulic permeabilities were measured before and after helium gas was applied to permeate the mixtures. Although gas formed preferential migration paths through the mixtures, the imperviousness of the bentonite/sand mixtures to the tested fluids never deteriorated because the paths became filled by swelling bentonite on re-saturation.