吐哈盆地中上三叠统砂岩储集层钻前孔隙度定量预测

对控制吐哈盆地中上三叠统砂岩储集层孔隙度的主要因素研究表明,热成熟度与砂岩孔隙度密切相关,而热成熟度又受地温场和埋藏史的控制。时间-温度指数可以综合反映热成熟度。当时间-温度指数大于115时,中上三叠统砂岩将变得致密。中上三叠统砂岩发育渐进型埋藏、早缓晚快型埋藏和早快晚抬型3种埋藏方式,早缓晚快型埋藏最有利于孔隙保存。第1、第2种埋藏方式砂岩的时间-温度指数与深度的关系较好,由此计算出吐鲁番坳陷中上三叠统有效储集层深度下限平均为4100m.因此,依据砂岩储集层时间-温度指数与孔隙度和时间-温度指数与深度的两个定量关系,可以在钻前预测砂岩孔隙度和有效储集层的保存下限深度,现场应用表明,这种方法是可行的。

Pre-Drilling Quantitative Prediction of Sandstone Porosity of Middle-Upper Triassic Reservoir in Tuha Basin

The main controlling factor researches about sandstone porosity of Middle-Upper Triassic reservoir in Tuha oilfield indicate that thermal maturity is closely related to sandstone porosity, and its varied range is controlled by geothermal field and buried history. The thermal maturity is comprehensively reflected by time-temperature index. The index bigger than 115 means there exists the more dense sandstone of Middle-Upper Triassic reservoir. In three burial types of the sandstone, such as gradual type, slow-early and quick-late type and quick-early and rise-late type, the slow-early and quick-late type is the most favorable for the retention of the porosity. For the first and the second burial types, the time-temperature index of sandstone is well related to the buried depth of it, from which the effective depth of the Middle-Upper Triassic reservoir in Turpan depression can be calculated to average about 4 100 meters. Based on these correlations of time-temperature index vs porosity and time-temperature index vs burial depth, the preserved depth limit of sandstone porosity and the effective reservoir can be predicted before drilling. The case study shows that this method is feasible.