This paper was prepared for the Abnormal Subsurface Pressure Symposium of the Society of Petroleum Engineers of AIME, to be held in Baton Route, La., May 15–16, 1972. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.
An apparent relationship of the environment of deposition to the occurrence of abnormal high-fluid pressures in a sand-shale sequence of the subsurface South Texas Oligocene is established. The abnormal high pressures are generally encountered in the "downdip" facies, which consists of deltaic sediments of alternating inner neritic (includes brackish and nearshore marine) and middle neritic (shallow marine) depositional environments.
There is an abrupt change in the environment of deposition that seems to coincide with the top of the abnormal high-pressure zone.
This new approach to predicting abnormal high-pressured formations can be used at the well site.
The key to a better understanding of the problems and the solution to these problems associated with abnormal high-fluid pressures may be found in an understanding of the depositional environments and history of the sedimentary basin. In order to accomplish this, there may be a need for more workers to examine surface and subsurface rock samples.
Many workers have presented conclusions on abnormal high-fluid pressures encountered in boreholes throughout the world. Probably the Gulf Coast region of the U.S. is better known because of the numerous boreholes and the documentation available.
Many giant hydrocarbon accumulations are produced from normal pressured reservoirs, and probably the majority of fields are in this classification. However, giant accumulations have been discovered in abnormal high-pressured formations also.
Some questions that will be reviewed in this report are the following.
Why is it that abnormal high pressures are encountered by the drill bit in some bore-holes and not in others when drilled to the depth in the same region?
Are there any attributes of depositional conditions that are always associated with this phenomenon?
How can we better predict the occurrence of abnormal high pressures within a petroleum basin?