鄂尔多斯盆地寨科地区延长组长2油层组地层水化学参数特征及对致密油藏的指示作用

鄂尔多斯盆地寨科地区长2油层组油水分布关系复杂，地层水化学组分及其分布规律认识不清。基于此，对寨科地区长2油层组地层水矿化度、离子特征参数分布及其与致密油分布之间的关系进行了深入研究。结果表明，目的层的水型为CaCl₂型，地层水的矿化度、钠氯系数、脱硫系数、变质系数的平均值分别为39 805 mg/L、0.32、2.68、58.80，表明目的层整体封闭性较好，有利于油藏的保存。地层水化学特征参数与沉积相及砂地比之间具有较好的相关性，分流河道地层水矿化度、变质系数值大于分流间湾，脱硫系数和钠氯系数值小于分流间湾，表明研究区长2油层组分流河道封闭性好于分流间湾，更有利于油气的聚集；地层水矿化度值随砂地比的增加具有先增加后减小再增加的趋势；变质系数随砂地比的增加具有先增加再减小的趋势；脱硫系数和钠氯系数随砂地比的增加整体呈现出递减的趋势，总体而言，砂地比值越大的区域，其地层封闭条件越好，越有利于油气的聚集。综合研究认为，长2段低渗透致密油藏的聚集受多个地层水特征参数共同影响，地层水矿化度、变质系数、钠氯系数、脱硫系数可以作为延长组低渗透致密油藏甜点评价指标。其中，地层水矿化度和钠氯系数对油气聚集的指示作用好于脱硫系数，而变质系数对油气聚集的指示作用较弱。

Chemical characteristics of formation water of Chang 2 oil formation of Yanchang Formation in Zhaike area， Ordos Basin and its indication to dense oil reservoir

The distribution of oil and water in Chang 2 oil formation in Zhaike area， Ordos Basin is complex， and the chemical composition and distribution of formation water are not clear. Based on this， the distribution of formation water salinity， ion characteristic parameters and their relationship with tight oil distribution of Chang 2 oil formation in Zhaike area are studied in depth. The results show that the water type of the target formation is CaCl_2， and the average salinity， sodium-chloride coefficient， desulphurization coefficient and metamorphism coefficient of formation water are 39 805 mg/L， 0.32， 2.68 and 58.8， respectively， indicating that the overall sealing of the target formation is good and conducive to reservoir preservation. Formation water chemical characteristic parameters and the sedimentary facies and sand ratio has good correlation between， distributary channel formation water salinity， metamorphic coefficient value is greater than bay between distributary， coefficient of desulfurization and sodium chloride coefficient value is less than bay between distributary， suggests research district two reservoir group bay between distributary channel closed in shunt， more conducive to the accumulation of oil and gas. The formation water salinity increases first， then decreases and finally increases with the increase of sand-ground ratio. The metamorphic coefficient increases first and then decreases with the increase of sand-ground ratio. The desulfurization coefficient and sodium-chloride coefficient decrease with the increase of the sand-ground ratio. Generally speaking， the larger the sand-ground ratio is， the better the formation sealing condition is， and the more favorable the hydrocarbon accumulation is. The comprehensive study shows that the accumulation of Chang 2 low permeability tight reservoir is affected by multiple characteristic parameters of formation water， and the formation water salinity， metamorphism coefficient， sodium-chloride coefficient and desulfurization coefficient can be used as the sweet spot evaluation indexes of the low permeability tight reservoir of Yanchang Formation. Among them， formation water salinity and sodium-chloride coefficient are better indicators of hydrocarbon accumulation than desulphurization coefficient， while metamorphism coefficient is weak.