塔中古生界油田水的成因和混合的证据

Evidence for origin and mixing of oilfield waters from Paleozoic strata in Tazhong area

塔中地区奥陶系、志留系和石炭系油田水的主元素、微量元素、87Sr/86Sr、δD、δ18O及全岩的87Sr/86Sr测试结果表明，油田水相对于海水蒸发曲线，富Sr2＋、C-＋、CF而贫K＋、Mg2＋，系水-岩反应改造的产物。远高于海水的87Sr/86Sr值表明油田水具有钾长石等矿物溶解的影响。油田水87Sr/86Sr-1/Sr的关系显示具有两种混合趋势，一种是奥陶系油田水向上运移与志留系和石炭系油田水的混合，以及侧向上来自西北部富87Sr的油田水向东运移；另一种是低Sr的淡水与油田水的混合作用。油田水的运移与混合方向指示了油气运移或调整再分配的方向。

Oilfield water chemistry and isotopic compositions are measured from Paleozoic strata in the Tazhong area, Northwest China. The data show that the waters are characterized by enrichment of Ca, Sr, CF (Ca＋ Mg＋ Sr－ SO4－ HCO3, in meq/L) and depletion of K, Mg relative to seawater evaporation trajectory, suggesting a result from water- rock interaction. Dissolution of Rb- enriched minerals, such as K- feldspar, contributed high 87Sr/86Sr ratios of the waters ranging from 0.710 26 to 0.712 90, which are larger than seawater at the time of deposition. Relationships between 87Sr/86Sr and 1/Sr of oilfield water give evidence of two mixing trends. One trend is that 87Sr- enriched water migrated eastward from Awati Depression, and the Ordovician oilfield water migrated upward; the other trend shows mixing with meteoric water of low Sr. The direction of oilfield water migration is consistent with that of oil migration.