Research on Rock Minerals and IP Response Characteristics of Shale Gas Reservoir in Sichuan Basin

Abstract

As a kind of clean energy, shale gas has attracted much attention, and the exploration and development potential of shale gas resources in the middle and deep layers is huge. However, due to the changeable geological and burial conditions, complex geophysical responses are formed. Therefore, studying the characteristics of reservoir rock minerals and their complex resistivity response characteristics is helpful to deepen the understanding of the electrical characteristics of shale gas reservoirs and provide theoretical basis and physical basis for exploration and development. The study is based on shale samples from the Longmaxi Formation to the Wufeng Formation of a shale gas well in southern Sichuan, China, and the mineral composition and complex resistivity of shale are measured. Through inversion of complex resistivity model, four IP parameters, namely zero-frequency resistivity, polarizability, time constant and frequency correlation coefficient, are extracted, and the relationship between mineral components of rock samples and IP parameters is analyzed. It is found that the polarizability gradually increases and the resistivity gradually decreases with the increase in borehole depth. With the increase in pyrite content, the polarization increases and the resistivity decreases. The corresponding relational model is established, and it is found that the polarizability is highly sensitive to the characteristic mineral pyrite, which provides more effective data support for the subsequent deep shale gas exploration.

High coincidence rate of fluid identification of carbonate reservoirs in Yan'an gas field by gas logging bright spot -resistivity dark spot technology

“…Both pyrite and formation water will lead to the reduction of reservoir resistance, and conventional logging interpretation cannot be accurately distinguished, resulting in a low coincidence rate of logging interpretation of carbonate reservoirs in this area. [9,10] The average pressure coefficient of the Majiagou Formation in Yan'an gas field is 0.814, and the specific gravity of drilling fluid in this area is generally about 1.1, which is a typical overbalanced drilling, resulting in low-resistance mud invasion. [11][12][13] However, for gas logging, overbalanced drilling makes the amount of formation oil and gas intrusions into the drilling fluid very low, and the total hydrocarbon base value is very low.…”