Abstract: Early authigenic chlorite cementation is of significant effect on the conversion, preservation and reconstruction of primary pores, based on the casting thin section and SEM analyses of Triassic Yanchang formation of Jiyuan area in western Ordos basin. It mainly occupies primary pores, converting them into intercrystal pores of clay minerals which can impede the damages of siliceous and carbonate cements to the pores, providing pathways for late fluid reconstruction of reservoirs. Its oil-wet clay mineral attributes provide condition for late hydrocarbon accumulation in low porosity and low permeability reservoirs. Also, the sensitivity of clay minerals should be taken into consideration when developing chlorite cemented reservoirs due to chlorite’s active and easy hydrolysis chemical properties. Though previous studies show an increase in compressive resistance in chlorite cemented reservoirs, this article demonstrates high compactions after the growth of grain-coating chlorite, which means such a compressive resistance may be overstated.

Key words: Ordos basin, Yanchang formation, authigenic chlorite, reservoir, carbonate cement, siliceous cement