典型陆相开放性断陷湖盆水化学场响应——以渤海湾盆地沾化凹陷为例

Response of the typical fresh formation water chemical fields in opening lacustrine faulted-basin:A case study of Paleogene system in Zhanhua sag

通过对沾化凹陷古近系1 160条数据体的试油资料,内容包含矿化度、水型、各离子含量(氯离子、钠离子、钙离子、镁离子、碳酸氢根离子、硫酸根离子等)、原油物性(原油密度、粘度、凝固点及含蜡量等)的分析,对沾化凹陷古近系的水化学场特征进行了研究,研究结果表明,与东营凹陷古近系沙河街组三段与四段封闭性滞留型水化学场特征明显不同,沾化凹陷古近系在宏观上呈现一系列开放性敞流湖盆水化学场的重要特征:矿化度及各离子含量较低(矿化度平均在10 g/L左右),平面上水化学场环带状特征及剖面上的分带性不明显,而主要呈现平面的分区性及剖面的旋回性;主要发育NaHCO_3型地层水(比例达到80%),变质系数、碳酸盐平衡系数高(分别在1.0和50以上),显示地层水变质作用及交替活动能力强;不同类型地层水Cl^--HCO_3^-响应有明显差异,低矿化度NaHCO_3型地层水rCl^-/r(HCO_3^-)比值基本小于10,表明研究区溶解、溶蚀作用明显;少量Ca^(2+)和Mg^(2+)负相关性显示,在研究区这种白云岩化作用主要发生在CaCl_2型地层水中;Na^+-Ca^(2+)关系显示,Na相对亏损、Ca相对富集特征不明显,代表Ca的相对富集数量的流体线(Ca_(excess)=0.997 4(Na_(deficit))+29.355(R^2=0.859 6))远低于世界平均盆地流体线;原油物性响应明显,研究区大多次生稠油分布在低矿化度型地层水中,显示了原油在开放性敞流型湖盆地层水载体中发生运移、聚集时的稠化作用。受湖盆中各次级洼陷的不均衡性发育和演化,研究区这种总体开放性敞流湖盆水化学场特征并不排除局部(如渤南洼陷)有封闭性滞留型湖盆水化学场特征。

On the basis of calculation and analysis of 1160 testing datum including salinity, formation water types, content of each ion such as Cl^-, Na^＋ , Ca^2＋ , Mg^2＋ , HCO3^-, SO4^2- , and physical property of crude oil such as density, viscosity, freezing point, paraffin content the formation water chemical field of the Paleogene system of Zhanhua sag was investigated. The results showed the obvious differences to the characteristics of the sealing and stagnating formation water chemical field of the Paleogene system of Dongying sag,the formation water chemical field of the Paleogene system of Zhanhua sag had typical characteristics of opening lacustrine faultedbasin：the content of total salinity and ions were low （total salinity averaged 10 g/L）, the characteristics of cyclic section were obvious, and the characteristics of circle in plane and zonality in section were not obvious; 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; the low value of rCl^-/r（HCO3^-） of most samples of the type of NaHCO3 formation water demonstrated the noticeable dissolution and corrosion,and the negative correlation between the contents of Ca2 and Mg^2＋ from some samples manifested the dolomitization was mainly occurred in the type of CaCl2 formation water; the deficiency of Na^＋ and excess of Ca were not remarkable, and the relation of them presented Ca = 0. 997 4 （ Nadeficit ） ＋29. 355 （ R^2 = 0. 859 6） ; the physical property of crude oil had marked response, and most secondary high viscosity oil samples were from the formation water with low salinity, which indicated the viscosity of crude oil in the history of hydrocarbon migration and accumulation in the opening environment. The macroscopic typical characteristics of formation water chemical fields in opening lacustrine faulted-basin not ruled out some sealing and stagnating formation water chemical fields in some areas such as Bonan subsag.