姬塬地区长9油层组地层水化学特征及其与油藏的关系

Hydrochemical characteristics and relationship between formation water and hydrocarbon reservoirs for Chang 9 in Jiyuan area

关键词:  鄂尔多斯  长9油层组  水化学参数  油气运移  地层水与油藏勘探

Key words:  Ordos Basin  Chang 9 reservoir  hydrochemical parameters  oil and gas migration  formation water and reservoir exploration

摘要:

基于地层水分析数据对姬塬地区长9油层组的地层水化学特征进行分析,在研究长9油藏主控因素的基础上,分析长9油层组原油地化参数与地层水化学特征,探讨长9油层组地层水化学特征与油藏的关系。结果表明:长9油层组地层水矿化度平均为28.7 g/L,地层水类型主要为CaCl₂型,其次为Na₂SO₄型及少量MgCl₂型和NaHCO₃型,属于整体封闭的,局部相对开放水文地质环境;从油藏运移的角度来看,长9地层水矿化度与示踪油气运移方向的地球化学参数(nC₂₁-+nC₂₂⁺)/(nC₂₈+nC₂₉)及nC₂₁-/nC₂₂⁺比值有着良好正相关性,长9油藏总是从低矿化度区域向高矿化度运移,且在运移路径上均存在显示地层水化学异常的Na₂SO₄型和NaHCO₃型地层水,其一定程度上可作为断层及裂缝等优势运移通道存在的响应,同时CaCl₂型地层水可作为良好的油藏保存条件的响应,因此长9油藏大多分布在Na₂SO₄型和NaHCO₃型地层水分布区域附近的CaCl₂型地层水中;结合油藏分布区地层水化学参数的分布,提出长9油藏聚集的有利水文地质条件。

Abstract:

The chemical characteristics of the formation water of Chang 9 reservoir in Jiyuan area was analyzed on the basis of the stratigraphic water analysis data. The crude oil geochemical parameters and the formation water chemical characteristics of Chang 9 reservoir were investigated in terms of the main controlling factors, through which the correlation between the formation water chemical characteristics and the reservoir of Chang 9 oil-bearing formation was discussed. It is found that the average salinity of the formation water in Chang 9 reservoir is 28.7 g/L. The main types of formation water are calcium chloride type, followed by sodium sulfate type and a small amount of magnesium chloride type and sodium bicarbonate type. And the hydrogeological environment is generally closed and partly open. From the perspective of reservoir migration, there is a good positive correlation between the salinity of the Chang 9 formation water and the geochemical parameters of the trace oil and gas migration direction ((nC₂₁-+nC₂₂⁺)/(nC₂₈+nC₂₉) and nC₂₁-/nC₂₂⁺). The Chang 9 reservoir always migrates from the low salinity area to the high salinity. And there is sodium sulphate type and sodium bicarbonate type formation waters showing the formation water chemical anomalies on the migration path, which can be used as a response to the existence of dominant migration channels such as faults and fractures. At the same time, the calcium chloride type formation water can be used as a good reservoir storage condition. Hence Chang 9 reservoir is mostly distributed in the calcium chloride type formation water near the sodium sulfate type and sodium bicarbonate type formation water distribution area. Finally, combined with the distribution of chemical parameters of formation water in the reservoir distribution area, the favorable hydrogeological conditions for the accumulation of Chang 9 reservoir are proposed.