摘要
井地电阻率成像法是一种电磁勘探方法,是一种将电测井法和地表直流电法相结合的综合勘探方法,它的基本原理是将供电源放置在一定深度的井中,在供电过程中测量地表各个电极的电位值,来反映井间地层与地层异常体的特征,而且能够增强测井在横向方向上的探测能力,成为以后电法勘探开发中一种非常重要的技术手段。本论文根据井地电阻率成像法有别于其他地球物理勘探的优势,着重研究井地电阻率成像法的数值模型,研究地下异常体对地表电位的影响,从而使得反演结果能更加准确可靠,并且可以应用到多个工程领域内。
首先,根据有限差分和差分方法的拉普拉斯方程进行了正演模拟,通过建立不同形式的地电模型(均匀介质模型,高阻块体介质模型,低阻块体介质模型,水平两层介质模型,垂直两层介质模型)来对地表电位进行正演模拟,从正演模拟出的地表电位可以看出不同的介质模型条件下,模拟出的地表电位是不同的,这是因为地下异常体对地表电位的影响的不同造成的,随着深度的增加这种影响会逐渐减弱；其次,而在反演过程中利用的是位场延拓方法和光滑约束最小构造的方法,将正演模拟得到的地表电位用反演方法进行计算,对地下异常体的形状位置进行反演,分析处理反演得到的电阻率切片,并与正演模型进行对照比较,得出通过本文的反演计算法,在水平和垂直方向上对异常体的反应理想,在深度上对异常体的分辨较好,证明该反演方法在对异常体的数值模拟上是可行的,能够得到理想的效果；最后,为了验证本文正反演方法在实际工程应用中的可行性,在某地区的高含水剩余油田中进行了现场数据测试,并对测得的数据应用本文的反演计算法进行了处理,最后为了验证反演电阻率的效果,与高含水油田剩余油的饱和度进行了比较,效果理想满足实际工程的需要,也证明该方法是切实可行的。
因此,通过本文正反演方法模拟出的不同介质模型的最终结果和实际工程应用,可知本文研究的井地电阻率成像法有着现实指导和借鉴的作用,尤其是在高含水油田中建立了不同原油性质、地层水介质条件下的电阻率与饱和度的配套解释方法,较为理想的分辨出高含水油田的油水界面,不仅能够为高含水油田剩余油动态监测提供另一种技术支持,更好的为油田的多次开采服务,而且还能够将该方法拓展到其他勘探领域,包括固体矿产资源勘探领域,矿产开采过程中安全监测领域,地下水污染环境监测评价,环境资源的监测领域,水文地质调查领域,工程勘察领域,考古学领域以及与实际生活密切相关的市政工程领域等,为满足不同工程的需要提供了新的途径。
Method of tomography of borehole-to-ground resistivity is one of electromagnetic exploration methods, which comprehended electric logging method and resistivity method. Concise introduction of this method can be showing from the following sentence. Putting one power source in some depth in well and then surveying every pole potential on the surface is the method principle. Through this method, the characters of stratums among boreholes would be directly responded. The technology of tomography of borehole-to-ground resistivity has its own vantages if compared with other exploration methods. One of the most important parts in this dissertation contains designing of numerical model that is viable for researching on the anomalous body exists in underground. Through founding enough numerical models and finding optimal method, besides, the following content plays important role on the total dissertation.
First, according to finite-difference method and anomalous potential Laplace equation, the forward models with several variations were designed, contained homogenous medium model, high resistivity block model, low resistivity block model, horizontal layer medium model, vertical layer medium model. Relying on these forward models, surface potential used for inversing medium resistivity was simulated, and following the increase of depth, the value of surface potential decreased obviously. Second, using the surface potential from forward model to inverse the anomalous body by method of continuation of potential field and smooth constraint minimal constructor, the resistivity slice about exact depth in rang of anomalous body burial depth could be achieved, which the forward models needed to compare with. The results of contrast among them verified in horizontal and vertical direction the inversion method had desirable consequent, besides, in depth direction the resolution was also ideal. Finally, to consider the numerical imitation should be applied in the engineering, this method the dissertation research on was used in some waterflooding oilfield, and gained resistivity slice by the dissertation method. In order to testify the result veracity, by virtue of diagram of degree of oil saturation the contrast about anomalous district between resistivity slice and saturation was anastomotic. The method can be available for the waterflooding oilfield.
Therefore, through simulating different models with the forward method and applying in the engineering with inversion method, the forward method and inversion method in this dissertation has practical significance and can be learned. Especially, in the waterflooding oilfield, one system of interpretation of detecting oil and water is set up, which can be available for distinguishing the interface of oil and water by different characters of oil and water. Consequently, it can service for enhancing oil recovery in waterflooding oilfield. By means of serving for enhancing oil recovery with this method, which can be opted to apply in other field of technical engineering, such as solid mineral resources exploration fields, safety field of monitoring mineral mining, monitoring and evaluation of environmental pollution in groundwater fields, environmental resources monitoring fields, hydrogeology survey fields, engineering prospecting areas, archeological fields and municipal engineering, etc, so in order to satisfy the needs of different engineering field, this method provides a new way to achieve significant influence.
引文
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