碳酸盐岩地层自然电位测井方法适用性分析及现场应用

Applicability Analysis and Field Application of the Spontaneous Potential Logging Method in Carbonate Rocks

摘要: 前人研究认为碳酸盐岩地层中自然电位测井的应用效果较差，相关评价方法很难使用。然而，近年来研究发现当满足一定条件时，该测井方法具有定性及定量解释效果。为分析自然电位测井的适用性，本文依据电化学原理讨论了渗透压力、矿化度差异、离子迁移率等影响自然电位的影响因素，对钻井液与地层水溶液矿化度差异、地层岩石物性、泥质、油气等因素的微观影响机理进行分析。结合国内外不同地区实际资料，认为碳酸盐岩地层中影响自然电位测井应用效果的主要因素包括岩石物性、泥质含量及其变化、井筒环境矿化度差异、孔隙类型以及目的层厚度。在此基础上介绍利用自然电位测井开展碳酸盐岩地层岩性识别、流体性质判别和地层水电阻率计算等方面的应用，最后对应用过程中发现的问题做出讨论。本文为自然电位测井用于碳酸盐岩解释和评价提供了借鉴。

Abstract: The spontaneous potential logging (SP) was considered as the invalid method in carbonate formation for a long time. The relevant evaluation approaches are difficult to be applied as well. However, recent field observations illustrated that SP log is qualitative and quantitative way to evaluate formation properties in carbonate rocks under particular conditions. To match that gap, based on electrochemical fundamentals, this paper discussed microscope parameters influencing spontaneous potentials, such as osmotic pressure, the difference of salinity, and transport mobility of ions. In addition, their relationships with macroscope factors were discussed, such as reservoir physical properties (porosity and permeability), the contrast of salinity between drilling fluid, and reservoir porous water, the volume of shale and oil-bearing saturation. According to field examples from areas of Sichuan, Qinghai, and Xinjiang in China and Central Asia, we contained that the key factors applying SP methods in carbonate formation are reservoir physical properties, volume of shale and that difference, the contrast of salinity in borehole environment, types of pore space and target layer’s thickness. The SP methods were successfully applied in evaluating lithology, fluid type and estimation of formation water resistivity in the fields. This paper also discussed problems and different viewpoints according to SP logging application. This study provides the knowledge for applications of SP logging method in carbonate rocks.