Study Of Hetaoyuan Formation's Reservoirs Forming Rules And Exploration Potential In Nanyang Depression

Through thirty years'exploration, most of the structural reservoirs which are easily discovered have been found in Nanyang Depression. Otherwise the difficulty of exploration and development is increasing with the complicated subtle reservoirs. So carrying out the study of hydrocarbon accumulation rule is the key to implement the next exploration under the complex hydrocarbon accumulation conditions and severe situation of oil production. Therefore, adopting the advanced experimental analysis means, systematic research thoughts and comprehensive disciplinary methods can further explain the structure and evolution characteristics of the inland fault-depression lake basin, the sedimental features and basic rule of through-going of reservoir bodies, oil/gas generation and migration, reservoir formation and distribution in Hetaoyuan Formation in Paleogene. Meanwhile, it will provide the basis of new decision-making for oil and gas exploration in new areas.The planar distribution feature of the southern boundary fracture of Nanyang Basin (Xinye Fracture) is like"Z". The understanding of the controlling function to sediment has been put forward based on comprehensive studies, i.e . several producing hydrocarbon centers have developed along the fracture; the distribution feature of the positive structures formed by several causes puts up zonary; different hydrocarbon accumulation zones have been developed through coupling the positive structures and the sand-bodies. The oil/gas secondary migration features have been analyzed by using nitrides in crude oil. The obvious diversity of the secondary migration has been brought forward in Weigang, Zhangdian and Dongzhuang Oil-fields.The hydrocarbon generation and drainage modes have been built up through the systemic evaluation of source rocks and crude oil. The crude oil in North Weigang area is mainly from the low-mature source rock (vitrinite reflection Ro=0.5～0.7%) in Sub-depression Niusanmen in Member Hetaoyuan-3. The oil source in South Weigang area is from source rock in Subdepression Niusanmen and Dongzhuang in Member Hetaoyuan-2 and 3, and belongs to the early, middle and late composite hydcarbon accumulation. The condition of reservoirs formation has been comprehensivly analyzed ,and the oil/gas migration-accumulation and reservoirs formation modes have been built up by using the basin simulation theoretics, i.e. the reservoirs formation mode in Weigang area is faulted-nosed and faulted-blocked, one central fault controls the distribution of oil/gas mature degree and the accumulation degree and oil/gas migration is mainly lateral, minorly vertical; the mode in Zhangdian area is faulted-nosed,and there is no interzone vertical migration for crude oil; the mode in Dongzhuang area is faulted-anticlinal, oil/gas migration is mainly vertical.Through research, 18 exploration wells have been deployed with newly increased oil in place 276×10~4 t, the probable reserves 562×10~4 t, thus the oil resources and exploration direction has been predicted.