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 r_Na⁺/r_Cl^- and［r_HCO^-3+r_CO^2-3］/r_Cl^-(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.

Key words: Jiyang Depression, Zhanhua Sag, Paleogene, evolution of lacustrine basin, faulted lacustrine basin, response of formation water chemical fields, salinity and water types

摘要： 通过对沾化凹陷古近系1160条数据体的试油资料、原油物性资料的分析，对沾化凹陷古近系沙河街组四段到东营组的水化学场特征进行了研究，结果表明：沾化凹陷古近系水化学场分布特征与湖盆演化的旋回性有良好对应关系，从湖盆的断陷初期阶段到断陷鼎盛阶段（沙河街组四段到三段），湖盆水体加深及淡化，矿化度及氯离子含量平均值逐渐下降；而在湖盆的总体萎缩阶段（从沙河街组二段到东营组沉积期），水体总体变浅，矿化度及氯离子含量平均值总体增大。在各阶段，地层水类型均以NaHCO₃型占绝对优势（比例达到80％），显示了典型的开放型湖盆的地层水场特征。NaHCO₃型地层水主要分布于地层水矿化度较低（<15 g/L）的地层中，指示了水交替活动强烈的开放水文环境，对油气保存不利；而相对较高矿化度（≥15 g/L）的NaHCO₃型地层水主要分布于生烃洼陷（渤南洼陷等）内部及义东断裂构造带附近，其成因主要与油气田形成和高含量的、以深部幔源为主的CO₂气及断裂沟通有关，其对应的原油密度基本小于0.9 g/mL，指示了相对有利的油气保存环境。

关键词: 浏阳坳陷, 沾化凹陷, 古近系, 湖盆演化, 断陷湖盆, 水化学场响应, 矿化度与水型

CLC Number: 

• P592