自然电位测井小短文译文.docx

spontaneous potential,simple sp log Spontaneous potential, self potential. The difference of potential (DC voltage) between a movable electrode in the borehole and a distant reference electrode usually at the surface. The SP results from the IR drop measurable in the borehole produced by the flow of SP currents in the hole. These currents are generated by the electrochemical and electrokinetic potentials. In impermeable shales, the SP tends to follow a fairly constant shale base line. In permeable formations, the deflection depends on the contrast between the ion content of the formation water and that of the following: drilling mud filtrate, the clay content, the bed thickness and resistivity, hole size, invasion, and bed boundary effects, etc. In thick, permeable, clean, nonshale formations, the SP value approaches the fairly constant static SP value which will change if the formation water salinity changes. In dirty reservoir rocks, the SP will not reach the same value, and a pseudo-static SP value will be recorded. The SP is most useful when the mud is fresher than the formation water, a good contrast exists between mud filtrate and formation water resistivities, and formation resistivity is low to moderate. In these cases, it indicates permeable beds by large negative deflections, permits easy sand-shale discrimination, is useful for correlations, and under favorable conditions, can be used for the estimation of formation water resistivity. The curve still remains useful in some saline muds. If the formation water is less saline than the mud filtrate, the SP deflection will be positive. However, when the mud column becomes so conductive it will not support a demonstrable IR drop, the SP curve becomes featureless. 自然电位测井（简称sp log）自然电位测井法：测量井眼中可移动的电极和通常在地表放置的远处参照电极的电位差。自然电位是由于井眼中由自然电位电流的流动产生的可测量的电压下降产生的。这些电流是电气化学和动电学电势引发的。在非渗透页岩中，自然电位趋近于相当稳定的页岩基线。在渗透层中，自然电位的偏移是由于地层水离子含量前后的差异、钻井的泥浆滤液、粘土含量、地层厚度和电阻率、井孔尺寸、干扰和地层界面影响等。在厚的可渗透的“干净的”新生地层中，自然电位值接近相当稳定的静自然电位值（只有当地层水盐度变化时才改变）。在“不干净的”储层岩石中，自然电位值不会达到相同值，这时一个拟静力电位值将被记录下来。当泥比地层水更新鲜时自然电位测井最有用，泥浆滤液和地层水电阻率形成一个很好的比较，地层电阻率降至中等。在这种情况下，自然电位测井能通过大的负偏差标示出渗透层，能进行简单的砂泥岩区分，对研究他们的相互关系很有用。在适宜条件