Response of formation water chemical fields to evolution of lacustrine basin of the Paleogene in Zhanhua Sag of Jiyang Depression and its hydrocarbon significance
Chen Zhonghong1, Wang Li2, Yang Yong3, Zha Ming1
1 College of Geo-Resources and Information， China University of Petroleum(East China)， Dongying 257061， Shandong 2 Petroleum Developing Center in Shengli Oilfield， SINOPEC， Dongying 257061， Shandong 3 Exploration and Development Research Institute， SINOPEC, Beijing 100083
Abstract：On the basis of calculation and analyses of 1160 testing data including salinity， formation water types， content of ions and physical properties of crude oil， the Paleogene formation water chemical field in Zhanhua Sag was investigated. The results show that the formation water chemical field has a good response to the evolution of lacustrine basin， the average salinity and content of ions decreased with the lake level deepening and desalinating from the initial faulted stage to the peak stage of fault development(the Member 4 to Member 3 of Shahejie Formation);The average salinity and content of ions increased with lake level shoaling in lake basin withering period(the Member 2 of Shahejie Formation to the Dongying Formation). Typical characteristics of an opening faulted lacustrine basin were displayed by the low content of total salinity and ions(total salinity averaged by 10 g/L)， NaHCO3 formation water being the dominant type(with a proportion of 80％)， and the high values of rNa+/rCl- and［rHCO-3+rCO2-3］/rCl-(the average values respectively higher than 1.0 and 50)， which indicated the stronger metamorphic process and alternation of the formation water. Influenced by the opening formation water chemical fields， the viscous crude oil was widespread and the widespread secondary heavy crude oil was the result of water-flush， oxidization and biodegradation in the course of oil migration， accumulation and preservation in opening formation water chemical fields. The samples with NaHCO3 type were mainly distributed in the formation water with a lower salinity（<15 g/L）， which indicated the opening hydrogeology and unfavorable preservation conditions for hydrocarbon. The formation water of NaHCO3 type with a higher salinity（>15 g/L）was mainly distributed in the Bonan subsag and the Yidong faulted zone. Its origin was relative with oil and gas fields and a high content of CO2 from mantle by the connection of faults， and correspondingly the density of crude oil was lower than 0.9 g/mL generally， which indicated favorable conditions for hydrocarbon preservation.
Chen Zhonghong,Wang Li,Yang Yong et al. Response of formation water chemical fields to evolution of lacustrine basin of the Paleogene in Zhanhua Sag of Jiyang Depression and its hydrocarbon significance[J]. JOPC, 2009, 11(5): 551-560.
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