Borehole-to-surface electrical imaging （BSEI） uses a line source and a point source to generate a stable electric field in the ground. In order to study the surface potential of anomalies, three-dimensional forward modeling of point and line sources was conducted by using the finite-difference method and the incomplete Cholesky conjugate gradient （ICCG） method. Then, the damping least square method was used in the 3D inversion of the formation resistivity data. Several geological models were considered in the forward modeling and inversion. The forward modeling results suggest that the potentials generated by the two sources have different surface signatures. The inversion data suggest that the low- resistivity anomaly is outlined better than the high-resistivity anomaly. Moreover, when the point source is under the anomaly, the resistivity anomaly boundaries are better outlined than when using a line source.
In the Yongjin oilfield of southern Junggar Basin, many wells have been drilled to produce industrial oils. Based on the analysis of fluid inclusions in the reservoirs, in combination with the geological and thermal evolution, the charge history in this area has been studied. The results indicate that the Jurassic Formation and Cretaceous Formation reservoirs contain abundant oil and gas inclusions, and four types of fluid inclusions have been distinguished. According to the homogenization temperatures of the fluid inclusions, the hydrocarbons charged the Cretaceous Formation for two periods, one ranges from the Late Cretaceous period to the Eogene period, and the other ranges from the Neocene period to the present. The oil filling history is correlated with the oil source correlation analysis, which is controlled by the movement of the Che-Mo plaeo uplift. Overall, oil accumulation is characterized by the superposition of two sets of source rocks for two stages in the Shawan depression.
The microscopic response characteristics of nuclear magnetic resonance(NMR) are widely used for characterizing complex pore structures of rocks. Due to the prohibitive NMR experiment cost, numerical simulation was employed as an alternative approach to verify some theoretical aspects of NMR responses. Firstly, the basic principles of pore-scale NMR simulation based on random-walk method(RWM) were introduced. The RWM-simulated results were benchmarked with the analytical results for an ideal spherical pore model. Then, the effects of two numerical parameters, namely diffusion radius and walk numbers, were studied on the simulation accuracy. The simulation method is then applied to various pore models with different pore sizes and pore shapes filled with different fluids to study the microscopic NMR response characteristics. The numerical experiments are useful for understanding and interpreting NMR measurements and the simulation code provides a numerical tool to perform pixel-based digital rock analysis.
