Finite element method-based resistivity simulation and water saturation calculation of irregular laminated shaly sandstone

Shaly sandstone reservoir is one of the most significant targets in petroleum and gas exploration. However, the influences of various factors on the resistivity of irregular laminated shaly sandstone are yet to be determined, and it is extremely challenging to accurately calculate the water saturation. By considering shaly sandstone in Zhujiang Formation of Neogene in Pearl River Mouth Basin as an example, this research extracts the shale distribution form and the pore structure by image processing, simulates the resistivity of rock by finite element method, analyzes the influence of shale parameters on resistivity, and deduces the water saturation equation of shaly sandstone. Results show that, in shaly sandstone, shale distributes in irregular laminated patterns on a millimeter scale. The other clean sandstone areas have high porosity and the capacity to reserve oil and gas. At high water saturation states, the shaly sandstone mainly conducts electricity in the clean sandstone area and various shale parameters have minor influences on the resistivity of shaly sandstone. At low water saturation states, the shaly sandstone mainly conducts electricity in the shale area, the resistivity of shaly sandstone is very close to the resistivity of the water layer, and the reservoir is the so-called low resistivity reservoir. The conductive form of clean sandstone area and shale laminae tends to parallel but remains a noticeable difference from total parallel. The simulation results deduced that the water saturation equation of shaly sandstone is more accurate than other equations, which provides an innovative mindset to calculate the water saturation of shaly sandstone.