东营凹陷水化学场成因及其与超压系统耦合关系

Hydrochemistry field origin and its coupling relationship with overpressure system,Dongying depression

以研究区2000余口探井的实测地压和油田水化学资料以及149个流体包裹体古压力模拟结果等为基础,利用地层水中阴阳离子平衡关系和水-岩相互作用的特点,考察东营凹陷水化学场的成因特征及其与超压系统演化特征的耦合关系以及对原油保存条件的影响。结果表明:在垂向上,2.2 km之上常压系统(沙二段至馆陶组)地层水矿化度一般低于100 g/L,属于咸水,而2.2 km之下的超压系统(沙四和沙三段)部分地层水矿化度高于100 g/L,最高达336 g/L,属于盐水;在平面上,东营凹陷东部地层水矿化度高于西部,北带高于南部,沙三和沙二段高矿化度地层水在凹陷中心沿断裂带分布,沙四段地层水矿化度以东营北带洼陷区为中心呈环带状向外减小;在水化学场和超压系统耦合作用下,超压流体封存箱中的水-岩相互作用对凹陷中心氯化钙型高矿化度地层水的形成具有重要作用,高矿化度地层水的形成某种程度上受到沙四段蒸发岩地层中盐类溶解作用的影响;不同地区和层位的原油密度不同,在凹陷边缘常压带为开启的水文地质系统,地表水渗入作用导致地层水矿化度降低,原油的轻组分散失,密度增加,油气保存条件较差,而凹陷中心超压顶面附近和超压系统内部处于封闭性较好的水文地质系统,原油密度多小于0.9 g/cm3,油气保存条件较好。

According to the measured pressure of formation, hydrochemistry data from more than 2 000 wells in oilfield, and the paleao-pressure from 149 fluid inclusion thermodynamics modeling in Dongying depression, the mass balance relation of cation and anion was calculated to study the water-rock interaction. Based on these, the generation process of the formation water and its relation to the pressure evolution and oil preservation conditions were analyzed. The results show that in the ver- tical, the formation water salinity is lower than 100 g/L in the normal pressure system （from Es2 to Qp） with the depth above 2.2 kin, and the formation water belongs to salt water. The formation water salinity is higher than 100 g/L and the highest value is 336 g/L in the overpressure system （ Es4 and Es3 ） with the depth under 2.2 km, and the formation water belongs to saline. In the plane, the formation water salinity in the east of Dongying depression is higher than that in the west, and the salinity in the north is higher than that in the south. The high salinity formation water in Es2 and Es3 distributes along the fault zones of depression center. The formation water salinity in Es4 reduces from the center of north depression to the outside, exhibiting zonal distribution. For the coupling relation between hydrochemical field and overpressare system, waterrock interaction in overpressure fluid compartment has a signification impact on forming high salinity CaCl： formation water in the center depression. The forming of high salinity formation water was influenced by the salt dissolution of evaporite formation in Es4. The density from different member and area is different. The depression edge normal pressure zone is an open hydro-geological system. The formation water salinity is reduced by infiltration of surface water. The oil light components are lost and oil density increases. The oil preservation conditions of the zone are poor, but the top and inside of overpressure system in the center of depression is a closed hydro-geological system. Most of oil density is lower than 0. 9 g/cm^3 , and the oil and gas preservation conditions are good.