Differences of characteristics and genetic of reservoirs in Chang 91 of Yanchang Formation in Jiyuan area, Ordons Basin

Key words:  genesis of sand body  reservoir characteristics  Jiyuan area  Ordos Basin

Abstract:

Based on a large number of well data and core observations, the reservoir difference characteristics and genesis of Chang 9₁ in the Jiyuan area of Ordos Basin were analyzed using comparative analysis. The results show that the sand bodies of Chang 9₁ in the east of the study area have the characteristics of small thickness of single layer, poor longitudinal continuity, and medium-low structural maturity.The sand bodies of Chang 9₁ in the west of the study area are thick, good pore throat connectivity, with good physical characteristics, especially the permeability, and the oil layers are thicker than the eastern ones. The dual superposition effects of sedimentation and diagenesis result in the different reservoir characteristics between the east and the west. In the east, there are mainly two types of sand bodies, namely, underwater distributary channel and estuarine bar at the leading edge of meandering river delta, while braided river delta leading edge underwater distributary channel sands deposited are the main sands in the west. During the diagenetic evolution, the reduced porosity of the reservoir in the west with relatively coarse grain size sandstone and better pore throat structure was lower than that in the east due to compaction. The cementation has a great influence on reservoir physical properties. Early cementation has little influence on reservoir porosity in west, late cementation has a great influence on reservoirs in west, and the reservoirs became dense after late cementation. However, the early cementation has a great influence on the porosity of the eastern reservoir, and the reservoir becomes denser eventually after the early cementation.