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spontaneouspotential,simplesplogSpontaneouspotential,selfpotential.Thedifferenceofpotential(DCvoltage)betweenamovableelectrodeintheboreholeandadistantreferenceelectrodeusuallyatthesurface.TheSPresultsfromtheIRdropmeasurableintheboreholeproducedbytheflowofSPcurrentsinthehole.Thesecurrentsaregeneratedbytheelectrochemicalandelectrokineticpotentials.Inimpermeableshales,theSPtendstofollowafairlyconstantshalebaseline.Inpermeableformations,thedeflectiondependsonthecontrastbetweentheioncontentoftheformationwaterandthatofthefollowing:drillingmudfiltrate,theclaycontent,thebedthicknessandresistivity,holesize,invasion,andbedboundaryeffects,etc.Inthick,permeable,clean,nonshaleformations,theSPvalueapproachesthefairlyconstantstaticSPvaluewhichwillchangeiftheformationwatersalinitychanges.Indirtyreservoirrocks,theSPwillnotreachthesamevalue,andapseudo-staticSPvaluewillberecorded.TheSPismostusefulwhenthemudisfresherthantheformationwater,agoodcontrastexistsbetweenmudfiltrateandformationwaterresistivities,andformationresistivityislowtomoderate.Inthesecases,itindicatespermeablebedsbylargenegativedeflections,permitseasysand-shalediscrimination,isusefulforcorrelations,andunderfavorableconditions,canbeusedfortheestimationofformationwaterresistivity.Thecurvestillremainsusefulinsomesalinemuds.Iftheformationwaterislesssalinethanthemudfiltrate,theSPdeflectionwillbepositive.However,whenthemudcolumnbecomessoconductiveitwillnotsupportademonstrableIRdrop,theSPcurvebecomesfeatureless.自然电位测井（简称splog）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。在适宜条件下，还可以用于地层水电阻率的估算。在一些含盐的泥层里得到的测井曲线一直很有用。如果地层水比泥浆滤液含盐少，自然电位偏差将会有用，然而当泥饼导电性很好的时候测井曲线就不能表现出可论证的电压下降，因为在自然电位曲线上没有什么变化。