甲酸盐无固相钻井液对测井曲线的影响及校正

甲酸盐无固相钻井液具有保护环境、储层保护、抑制地层等优点.但是,由于甲酸盐钻井液密度较大,并且含有大量负离子,使得甲酸盐钻井液对测井曲线具有不同程度的影响,这为测井识别油水层、确定含油饱和度带来了一定的不确定性,增加了测井评价的难度.结合甲酸盐无固相钻井液密度大及侵入地层较深等特点,分析了该钻井液对井径测井曲线、密度测井曲线以及电阻率测井曲线的影响.使用有机盐钻井液体系钻井,对砂岩井段的井眼半径影响不大,对泥质含量相对较高的井段和泥岩段,由于井壁的垮塌现象减少,在这种情况下,单纯地靠观察井径的大小很难对岩性进行评价.甲酸盐无固相钻井液密度较大,侵入地层较深,在侵入地层特别是侵入的砂岩储层中密度测井值较高;由于钻井液电阻率低于地层电阻率,使得视电阻率较低,为油气解释造成了困难;随着浸泡时间的延长,甲酸盐钻井液对地层的影响也不尽相同,所以在钻后及时测井显得尤为重要.通过室内实验,得到了某地区甲酸盐钻井液的电阻率校正方法,并利用该方法处理了某油田的几口井,实际效果是可靠的.

Effect of solid free formate drilling fluid on well logging curves and the correction

The solid free formate drilling fluid has advantages of environmentally benign, reservoir protection and bore hole stabilization, whereas because of its higher density and the presence of a lot of negative ions, the fluid affect subsequent logging curves in different degree, bringing uncertainty in telling oil layers from water layers, making error in determining the oil saturation from logging curves. In this paper, incorporated with the characteristics such as higher density and deeper invasive depth into the formation by solid free formate drilling fluid, influence caused by this fluid on caliper logging curve, density logging curve and resistivity log curve were investigated. Results showed that, 1) when organic salt drilling fluid system was used, the hole radius in sandstone section was not influenced much, and in the well interval of high mud content or shale, appearance of hole collapse was not obvious. In this condition, it is inaccurate to evaluate the lithology simply from logging curves; 2) when the solid free formate drilling fluid was used, the filtrate invades deeper into the formation, the density logging data was higher, especially in sandstone; 3) for the resistivity of the fluid is lower than that of the formation, the apparent resistivity becomes lower, making difficulty in hydrocarbon identification, and with the soak time elongating, the fluid affect the formation in various ways, therefore, it become especially important to log in time. To solve above problems, a correction method for resistivity log in a given oilfield using formate drilling fluid was obtained based on lab tests. The method was applied in several wells and the results were reliable.