The sources and formation processes of brines from the Lunnan Ordovician paleokarst reservoir, Tarim Basin, northwest China
The sources and formation processes of brines from the Lunnan Ordovician paleokarst reservoir, Tarim Basin, northwest China
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DOI：
10.1111/gfl.12033
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发表时间：
2013-08
期刊：
影响因子：
1.7
通讯作者：
Jian Chen;Dehan Liu;P. Peng;Chi-ling Yu;Baoshou Zhang;Zhong-yao Xiao
中科院分区：
文献类型：
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作者：
Jian Chen;Dehan Liu;P. Peng;Chi-ling Yu;Baoshou Zhang;Zhong-yao Xiao
中国盆地西北部塔里木盆地最重要的油气勘探目标是古岩溶油气藏。为了解该类型储集层卤水的来源和演化规律，在轮南油田中下奥陶统古岩溶储集层采集了37个地层水样。δD-δ18O相关性和氯/溴比值反映了两种流体的混合：大气水和蒸发海水。不同的混合程度将样品分为两组。第一组样品，来自深部地层(5150-6667 m.b.s.l.)在油田东部，δD升高(−53.5~−38.0‰)，δ18O值0.6 6~5.99‰)，较低的氯/溴比(除LN 6 34-1和LN 63 1-1外)，形成于海水蒸发和大气降水的少量贡献。2组样品来自油田西部浅层(5038-6067m.b.s.l)，具有不同的特征(−59.6m.b.s.l至−48.5m.b.s.l)(‰D为δ59.6m.b.s.l至−48.5‰，δ18O为0.47m.47至2.17m.b.sl，氯/溴为501m.b.s.l)，反映了蒸发海水与高比例大气水的混合。这两种流体都与矿物交换了氧同位素。阳离子组成研究表明，在进入现今水库之前，水体经历了斜长石的钠长石化作用，大气降水溶解了蒸发岩，海水经历了白云石化作用。锶同位素(0.709801-0.711628)显示的混合趋势为两种流体类型的混合提供了进一步证据。基于地质历史与资料的关联，可以建立两种大气降水入渗模型。根据水的化学和同位素组成，确定了东部流体体系(第1组)和西部流体体系(第2组)。更好地了解地下流体运动规律，可能对局部勘探有所帮助。
The most important petroleum exploration target in the Tarim Basin, northwest China, is the paleokarst reservoir. To understand the source and evolution of brine in this type of reservoir, a total of 37 formation-water samples were collected from the Middle-Lower Ordovician paleokarst reservoir in the Lunnan oilfield. The δD-δ18O correlation and Cl/Br ratios reflect the mixture of two fluids: meteoric water and evaporated seawater. The different degree of mixture divided samples into two groups. Group 1 samples, from deep strata (5150–6667 m.b.s.l.) in the east of the field, with elevated δD (−53.5 to −38.0‰), δ18O values (0.66–5.99‰), and lower Cl/Br ratios (336–478 for Cl/Br, except LN634-1 and LN631-1) were formed by evaporation of seawater plus a small contribution from meteoric water. Group 2 samples, from shallow strata (5038–6067 m.b.s.l.), in the west of the field, have contrasting features (−59.6 to −48.5‰ for δD, −0.47 to 2.17‰ for δ18O, and 501 to 871 for Cl/Br), which reflect a mixture of evaporated seawater with a high proportion of meteoric water. Both of the fluid types exchanged oxygen isotope with minerals. The investigation into cation composition reveals that, before entering into the current reservoir, waters suffered albitization of plagioclase; moreover, meteoric water dissolved evaporites and seawater experienced dolomitization. A mixing trend showed by strontium isotopes (0.709801–0.711628) gave further evidence for the mixture of two fluid types. Based on the correlation of geological history with our data, two infiltration models of meteoric waters can be constructed. According to the chemical and isotopic compositions of the waters, an east fluid regime (Group 1) and a west fluid regime (Group 2) have thus been defined. Better understanding of the subsurface fluid movement patterns may be helpful for the local exploration.