柴达木盆地大风山凸起地层压力预测及成因分析

Prediction and genesis of formation pressure in Dafengshan uplift,Qaidam Basin

地层超压预测对油气成藏的研究具有重要意义。通过测井曲线组合、声波速度-垂向有效应力交会图、声波速度-密度交会图和超压综合分析等方法,对柴达木盆地大风山凸起各层位的超压成因进行了分析,并对压力预测方法进行了改进。研究结果表明:(1)柴达木盆地大风山凸起下油砂山组地层超压成因为不均衡压实和构造挤压作用;上干柴沟组和下干柴沟组上段超压成因为不均衡压实、构造挤压和超压传递。(2)用单一方法如平衡深度法或伊顿法均无法有效预测研究区的地层压力,基于不同超压成因机制的差异,对下油砂山组地层压力采用平衡深度法计算,对上干柴沟组和下干柴沟组上段则使用伊顿法计算,结果更准确。研究区压力计算结果与实测地层压力的误差小于7.00%,平均误差为4.30%。(3)超压的预测可为油藏描述、储量估算、安全钻井作业提供数据支持。超压是油气运移的动力,可以指示油气运移的方向,估算油气运移距离,对油气成藏的研究具有重要指导意义。

Overpressure prediction is of great significance to the study of oil and gas accumulation. By means of logging curve combination,cross plot of acoustic velocity and vertical effective stress,cross plot of acoustic velocity and density,and overpressure comprehensive analysis,the overpressure causes of each layer in Dafengshan uplift of Qaidam Basin were analyzed,and the pressure prediction method was improved. The results show that:(1)The overpressure of Xiayoushashan Formation in Dafengshan uplift of Qaidam Basin is caused by uneven compaction and tectonic compression,and the overpressure of Shangganchaigou Formation and upper Xiaganchaigou Formation is caused by uneven compaction,tectonic compression and overpressure transmission.(2)Single methods such as equilibrium depth method or Eaton method cannot be effectively used to predict the formation pressure in the study area. Based on the difference of different overpressure genesis mechanisms,the equilibrium depth method was used to calculate the formation pressure of Xiayoushashan Formation,and the Eaton method was used to calculate the formation pressure of Shangganchaigou Formation and upper Xiaganchaigou Formation,with more accurate results. The error between the calculated pressure and the measured formation pressure in the study area is less than 7.00%,and the average error is 4.30%.(3)Overpressure prediction can provide data support for reservoir description,reserve estimation and safe drilling operation. Overpressure is the driving force of oil and gas migration. It can be used to indicate the direction of oil and gas migration and estimate the distance of oil and gas migration,which has important guiding significance for the study of oil and gas accumulation.