沾化凹陷古近系现今水化学场响应及其油气意义

陈中红，等。古地理学报，2009，11（5）。

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，研究结果表明：沾化凹陷古近系水化学场分布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发展到断陷鼎盛阶段（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%），显示了典型的开放性湖盆的地层水场特征。NaHCO₃型地层水主要分布于较低矿化度（<15g/l）的地层水中，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（15g/l以上）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。

Response of Formation Water Chemical Fields to the evolution of lake-basin of the Paleogene system in Zhanhua sag and its significance to hydrocarbon accumulation

Chen Zhonghong et al.

Journal of Palaeogeography

On the basis of calculation and analysis of 1160 testing datum including salinity, formation water types, content of each ion and physical property of crude oil, the formation water chemical field of the Paleogene system of Zhanhua sag was investigated. The results showed that: the formation water chemical field had good response to the evolution of lake-basin, the averaged salinity and content of ions descended with the water-body deepen and desalination from the development to the peak of faulted lake-basin (Member 4 to Member 3 of Shahejie Formation), and the averaged salinity and content of ions increased with the water-body shoaling in the course of fade of faulted lake-basin (Member 2 of Shahejie Formation to Dongying Formation). Typical characteristics of opening lacustrine faulted-basin were displayed: the content of total salinity and ions were low(total salinity averaged 10g/l), mainly developed the type of NaHCO₃ formation water ( proportion attained 80%) , and the value of rNa⁺/rCl^- and [rHCO₃^-+ rCO₃^2-]/rCl^- were high (the average values respectively higher than 1.0 and 50), which displayed 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 reservation in the opening formation water chemical fields. The samples with NaHCO₃ type were mainly distributed in the formation water of lower salinity（<15g/l）, which indicated the opening hydrogeology and unfavorable reservation environment for hydrocarbon. The formation water of NaHCO₃ type with higher salinity （>15g/l）was mainly distributed in Bonan subsag and Yidong faulted zone, which indicated its course were relative to oil and gas fields and high content of CO₂ from mantle by the connection of faults, and the density of the crude oil accompanied with it was lower than 0.9g/ml generally, which directed favorable conditions for hydrocarbon reservation.