Abstract
Feldspar of lithosphere undergoes transformation in an acidic fluid environment. This process significantly influences the transformation of sandstone reservoirs in sedimentary basins. Currently, there is debate on the transformation mechanism, which has led to debates in predictions of favorable reservoirs in deep sedimentary basins, in terms of their origin, type, and distribution. In this study, the transformation process of feldspar is determined based on the total dissolution model, and thermodynamics is used in the calculation process. Firstly, the precipitation order of the minerals and the reaction path during the transformation process are determined. Secondly, the obtained results are compared with the results of weathered feldspar samples, laboratory-based physical simulation samples, and sandstone samples from a sedimentary basin. Finally, the changes of sandstone reservoirs which is caused by feldspar transformation processes are discussed. Based on those results, it can be deduced that the release of inter-granular particles (Na/K/Ca) in feldspar does not conform to the total dissolution model, whereas the release of lattice particles (Si and Al) conforms to the model. The total dissolution model can deduce the genetic mechanism and occurrence of authigenic kaolinite in sandstone reservoirs. When the temperature is below 120 °C, authigenic kaolinites are directly precipitated from the pore fluids or via the reaction of Al(OH)3(s) with H4SiO4(aq). The kaolinite aggregates are worm-like, with a pure chemical composition. When the temperature is above 120 °C, the feldspar particles react with Al(OH)3(s) and transformed to kaolinites. The kaolinite aggregates are particle-like, containing heteroatoms. The differences in the genetic mechanism of kaolinite lead to evident differences for type and distribution of secondary pores formed during feldspar transformation.
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