A review of the origins of pressures and a restatement of the definition of abnormal pressures is presented. Geologic interactions are presented as supporting evidence for the basic origins. A discussion of the various geologic maintenance theories are presented with supporting evidence.
The term "abnormal pressure" through general usage has come to mean higher-than-normal pressure encountered in the earth's crust while drilling. Some have defined these pressures as geopressures.
Normal is defined as the lithology gradient for a salt water basin. If so, we must accept any deviation from 0.465 psi/ft of depth as abnormal. Therefore, any fresh water or brackish water deposition must be called abnormal. There exists a normal for every geological setting, but since we drill far more wells in sediments associated with sea water deposition, 0.465 psi/ft of depth will be used as normal in this discussion.