Abstract:

The Chang 3 sandstone reservoir of Yanchang Formation in Jiyuan area is lithologic reservoir , which belongs to continental delta deposits. The framework sand body is delta front subsea distributary channel . The reservoir lithology is arkose and syrosem arkose , with the low maturity of lithologic composition and good texture maturity. The reservoir is typical low porosity and low permeability reservoir with average porosity of 12. 62 % and average permeability of 0 . 8 ×10^{- 3} μm² . Based on the data of SEM , cast slice cathodeluminescence and X diffraction etc. , the diagenesis of the study area was analyzed. The result showed that the third member of Yanchang Formation is now in the transition period from the early diagenetic stage B to late diagenetic stage A. In the early diagenetic stage , the stratum water circulating environment is a relative opened type of weak acid , and in the late diagenetic stage , it is a relative closed type of weak acid , which provide good conditions for denudation. The mechanical compaction , cementation and displacement result in the poor physical property of Chang 3 reservoir , and t he denudation is infavor of the reservoir.

Key words: low permeability, lithologic reservoirs, exploration and development, Ordos Basin