Characteristics and genetic mechanism of low-permeability reservoirs of the 4th member of Shahejie formation in Hexiwu structural zone of Langgu sag

Key words:  low-permeability reservoir  genetic mechanism  geophysical property inversion  diagenetic evolution  Langgu sag

Abstract:

Based on the data of thin section observation, geophysical property test, mercury injection test and fluid-inclusion temperature test, the characteristics and genetic mechanism of low-permeability reservoirs of the fourth member of Shahejie formation (Es₄) in Hexiwu structural zone of Langgu sag were studied by using the inversion method of the reservoirs porosity and permeability during the geological history.The results show that there are low porosity and extremely-low permeability reservoirs in Es₄ of Hexiwu structural zone. The sedimentary difference, which leads to different primary geophysical properties because of different material composition, grain size and sort, is the primary cause of low permeability. The diagenesis is the vital cause of low permeability. The rapid burial in early diagenetic stage, the cementation in later diagenetic stage and the lack of effective mechanism for increasing porosity and protecting pores form the low-permeability reservoirs finally. The method for inversion of the reservoirs geophysical property during the geological history can rebuild the evolutionary process of porosity and permeability.