Petrophysical Measurement And IP Effect Research Of Longmaxi Formation Shales

Shale gas resources have been proved rich in our country and show a tremendouse potential during the process of exploration and development. Lower Paleozoic Silurian Longmaxi Formation exposed in Sichuan Basin has a enormous mud shale deposits with high organic carbon content, ideal organic matter type and fairly important maturity conditions, which contribute the great attention being attached to this target including this paper. This paper introduced the causes and mechanism of IP effect, the potential equation and boundary conditions under the stimulation of direct current field, the theory basis of using equivalent resistivity method to obtain the quadratic field potential, and forward response of different depth-buried, position and size-set, even two separated layer models. The results show that different setting parameters of underground-model have a significant impact on the surface polarization response. What’s more, cole-cole expressions of real component, virtual component, amplitude and phase of complex resistivity were deduced in the study. According to dispersion curves of the four complex resistivity parameters, the varing characteristics of curves were discussed. As well, this paper collected 16 pieces longmaxi rock specimens respectively from Yichang FenXiang, Chongqing ShiZhu, Chongqing YuShan, Yichang WuFeng. Based on AutoScan-II platform on room conditions and Autolab-1000 platform on high temperature and pressure, tests of rock specimens’complex resistivity were conducted. The results show the value of four parameters of complex resistivity draw to varying degrees but frequency dispersion shape show no change, when the frequency is less than 10kHz, phase and heterogeneous resistivity have a positive correlation with the slope of amplitude curve. For ChongaQing ShiZhu samples, compared with other spots, IP effect of pyrite is the key factor of phase and heterogeneous resistivity’s dramatic dispersion. Because pyrite is the sign of rich organic matters, phase and heterogeneous resistivity can be used as the important indicators to detect target object in Lower Silurian Longmaxi Formation.