On Distribution of Natural Electric Field in Open Hole

The traditional model used to describe the distribution of natural electric field in open hole is interfacial potential that shows spontaneous potential distributes on the interface between formation and mud.Obviously,this model is insufficient to interpret some theory problems clearly.Based on modern electrochemical theory,proposed is a new model of natural electric field distribution in open hole.The model considers that natural electric field distributes in whole mud invasion zone,and forms potential grad along the invasion direction.The potential is higher near well section,and died away at the end of the invasion zone.So,the investigation depth of spontaneous potential logging is the depth of mud invasion,and relation between spontaneous potential and mud invasion depth may be built.The new model is complement and development to the traditional model.