The Calibration Of The Ultralow Permeability Measurement Apparatus And Preliminary Experimental Results

Rock is a kind of porous media in which fluid flow through pore channels is the most important process of rock material transportation, having substantial significance in environmental science, seismological structure and oil geology. Quantification of fluid transport through fault zones is critical for the prediction of subsurface fluid flow and understanding of fault mechanics. Permeability is an important controlling parameter of fluid flow systems at depth, ranging widely from more than 10-12m2 to less than 10-23m2 depending on the rock type and depth. Permeability measurement under high confining pressure in the laboratory is one possible way to predict permeability structure at depth. However, it is very difficult to measure the low-ultralow permeability accurately.In order to study experimentally the influences of permeability on fluid flow, fault healing and fault frictional strength in seismogenic regions, we have designed and constructed a distilled water/gas-medium permeability measurement apparatus in cooperation with SHIYI Technology Co. Ltd, China University of Petroleum in Shandong Province, which is capable of achieving ultralow permeability. The new apparatus uses the steady-state method and pore pressure oscillation method utilizing the amplitude attenuation and phase shift of a sinusoidal pressure wave across a sample, which has become very popular recently because of its continuous measurements during processes that might alter the pore space of rocks to measure samples with different permeability magnitudes fast and precisely. It can produce a basic environment in which the confining pressure reaches 200MPa by water, and pore pressure reaches 40MPa either by water or gas at room temperature. Simultaneous measurements of the upstream and downstream pressure permit the calculation of permeability and specific storage. The permeability measurement magnitude ranges from 10^-14-10^-21m². In this thesis, several measuring approaches are compared theoretically to acquaint their advantages and drawbacks. And the affecting factors, testing procedure and data processing way in pore pressure oscillation method are presented in detail. In this thesis, we have introduced some calibrating parameters in the pore pressure oscillation method and given the experimental results on typical sandstones under seasoning-cycle conditions. The experimental results show that: (1)permeability decreases with raising confining pressure while it increases with raising pore pressure; (2) permeability to the pore pressure oscillation method decreases with cyclic numbers slightly while it decreases markedly to the steady-state method; (3)the used empirical power law fits the experimental values and the accuracy to pore pressure oscillation method is extremely high. The test setup allows us to perform the experiments by means of pore pressure oscillation and steady-state method, so the two approaches are compared based on results gained from the same sample during the same experiment. And it is found that permeability of the pore pressure oscillation method is slightly larger than that of the steady-state method. Finally, this thesis discusses the reasons for the discrepancy due to the applied methods.Factors affecting the permeability from laboratory experiments are considered and quantified. Some preliminary research on the pore pressure shows that the effective pressure coefficient does not always equal to unity, and I have calculated effective pressure coefficients at intervals during the cycles. Large hysteresis in permeability has been observed, and the effective pressure coefficient has been found loading path dependent. At last, the least square method is used to the all experimental data, getting the optimal effective pressure coefficient to make the permeability results correlate well with the effective pressure. The mutual effects of confining pressure and pore pressure on permeability have been described.