油气藏识别中的地 井电磁正反演研究

Identification of oil and gas reservoirs using surface-boreholeelectromagnetic methods

地井电磁方法是一种极具潜力的油气藏识别方法,日益受到业界重视。为研究地井电磁方法有效识别各类油气藏分布的可能性,建立了相应的地面模型和地对井模型,采用基于电性源和磁性源的两种测量配置,配合不同的测量参数,通过正演模拟对地面模型和地对井模型进行浅层油气藏的灵敏度分析,比较得出性能最佳的测量模型、测量配置以及测量参数(如发射源的频率、发射源与接收器的间距)。进一步建立了一个地井双源模型。然后,基于该模型采用高斯牛顿法的反演方法对各类别油气藏进行反演研究。灵敏度分析发现,地对井模型对浅层油气藏极其敏感。不同模型的反演研究表明,采用地井双源模型能够对浅层油气藏进行精确反演;增设地面接收器的地井电磁方法能够较为准确地刻画1500 m深度的复杂油气藏的位置形态及断层背景;采用地井电磁与井间电磁联合反演可以较为精准地识别5000 m深度的典型缝洞型油气藏的大小与位置。抗噪实验证明,地井电磁方法可以有效提升井间电磁方法的勘测精度且具有一定的抗噪性能。此方法可以为实际生产提供帮助,即在缝洞型油气藏的后期开发当中,利用井间电磁结合地井电磁的方法可以实现对油气藏流体的监测和对其周围地层流体变化的监控。

The surface-borehole electromagnetic method of oil and gas reservoir identification has high potential and is becoming increasingly popular in the industry.Compared with the surface electromagnetic method,it has the advantages of a high signal-to-noise ratio and better detection of anomalies.To study the possibility of effectively identifying various types of reservoirs,survey models based on the surface electromagnetic method and surface-to-borehole electromagnetic method were established,and a sensitivity study was performed with both electric and magnetic sources and varying parameters.In addition,a surface borehole dual-source electromagnetic model was studied.Based on the results of the sensitivity analysis,the optimum model,configuration,and parameters(such as the transmitting frequency and distance between the transmitter source and receiver)were obtained.Subsequently,the inversion based on the Gauss-Newton method was used to image each type of reservoir,such as complex oil and gas reservoirs at a depth of 1500 m and typical fracture-cavity reservoirs at a depth of 5,000 m.Sensitivity analysis showed that the surface-to-borehole model had the best performance and was extremely sensitive to shallow reservoirs.Inversion studies of different models have shown that the proposed surface-borehole dual-source electromagnetic model can be used for accurate inversion of shallow reservoirs,the proposed surface-borehole method with additional surface receivers can achieve a more accurate description of the position and shape of the complex reservoir body and its fault background,and the joint inversion of the surface-borehole electromagnetic model and the cross-well electromagnetic model can effectively and accurately identify the size and location of typical fracture-cavity reservoirs at a depth of 5000 m.An anti-noise test showed that the surface-borehole electromagnetic method can effectively improve the accuracy of the cross-well electromagnetic survey for data with a relatively high percentage of noise.In the production of fracture-cavity reservoirs,joint surveys with cross-well electromagnetics and surface-borehole electromagnetics can be used to accurately monitor fluid movement in reservoirs and surrounding formations.