Study Of Chang 3 Oil-bearing Formation Of Ganquan Exploration Area In The Ordos Basin

Ganquan exploration area of Yanchang oilfield is located in the southeast margin of ordos basin.It includes Fuxian,Xiasiwan areas. The main oil-bearing horizon is Chang 3 reservoir, which are super-low permeability detrital reservior with flat structure and small angle, in the Triassic Yanchang formation. Nowadays, the reservoirs are still in the beginning development stage.This paper made Chai 44 well area of Xiasiwan oilfield as the major study-target, utilizing drilling, logging and large amount of analytical data, and taking advatages of the modern theories and techniques of reservoir evaluation, studied the reservoir petrology and diagenesis, physical properties characteristics and pore structure, reservoir heterogeneity and sensitivity, as well as the fracture characteristics of Chang 3 reservoir.The study shows that, Chang 3 reservior of Ganquan oilfield was located in the plain facies belt of Fuxian delta, its mian micro-phase types can be divided into distributary channel and margo lateralis, natural levee,crevasse splay,diversion among bay. The inter-distributary channel is the most advatageous sedimentary facies. The type of the reservoir rock was from gray-brown to gray debris-feldspar sandstone. Compaction,pressure solution,cementation dissolution and fracture diagenesis were main types of diagenesis. Intergranular pore was the mainly saving type of reservoir and residual dissolution pore followed. Follows intergranular pore was the main porous compositioni. The throat radius distribution interval of Chang 3 reservoir is 0.2-0.7μm, pore radius distribution interval is 100—200μm. The throat distribution curves offset thin, pore offset coarse,which are both normal single kurtosis.Pore of Chang 3 reservoir is macropore-fine pore,the connectivity and tortuosity of throat are important to permeability, which also controls reservoir property. The average value of the porosity and penetration rate of the reservoir were separately 12.4% and 0.73×10-3μm2,So Chang 3 reservoir was a lreservoir with the character of low porosity and low permeability. According to the classification standard of low permeability reservoir about ordos basin,Ⅲb chass, Iva chass account for 69% at most, IVb chass, V chass respectively account for 14%,17%,total isⅢb chass,Iva chass reservoir,which is super-low permeability reservoir. The heterogeneity of the reservoir showed as extremely unbalanced nature of the oil and gas distribution in the vertical and plane. The character of sensitivity of the reservoir was concentrated on the acid sensitivity damage, with alkali sensitivity and speed sensitivity as a secondary contradictions.According to field outcrop and experimental analysis date,shows that feature of fracture development trends mainly northeast-southwest, fracture azimuth is between 56°-80°, basically identical to the nasal axis trend of nose structure Chang3 oil reservoir is structural-lithological reservoir, reservoir lithology and physical properties control oil and gas distribution. High quality reservoir distribution area usually is gas enrichment area,local nasal uplift may play a role on gas enrichment,which is also the main oil producing area.