Abnormal Subsurface Pressures, Their Origin and Methods Employed for Prediction in India
Authors: Sahay Bhagwan 
Published: December 2007

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 publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made.

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Results of drilling carried out in India indicated the occurrence of abnormal high-pressure horizons generally below a thick section of shale in the sediments of Eocene-Pliocene age. The areas where the high pressures occur are below the Mio-Pliocene pressures occur are below the Mio-Pliocene unconformity in the geosynclinal region of Bengal basin, South Kadi and Nawagam areas of Gujarat in western India, Murrees (Eocene-Miocene) of Punjab and Jammu, northern India and the wells drilled on Masimpur structure in Assam. Different theories regarding the generation of abnormal high pressures in these sediments have been discussed.

The technique of predicting abnormal high pressures from the resistivity and density of pressures from the resistivity and density of shales in the wells drilled in the geosynclinal region of Bengal basin, where the generation of abnormal high pressures appears to be primarily due to the compaction of shale in response to the stress of overburden, was successfully tried and enabled the prediction of such horizons well in advance.

Introduction

Drilling operations carried out in various Illustrations at end of paper. parts of India indicated the occurrence of the parts of India indicated the occurrence of the abnormal high-pressure horizons in the sediments of Eocene to Pliocene age. They can be put into two categories, one in which there is a thick, highly folded, sand/shale sequence. Hence the generation of pressures is due to tectonics. The others belong to areas of very rapid deposition. In the first category are the Suruinsar well in Jammu and Kashmir State, Balh well in the Punjab and wells drilled on Masimpur structure in Assam. To the second category belong the wells drilled in the geosynclinal region of Bengal basin and South Kadi and Nawagam areas of Gujarat.

ORIGIN OF HIGH PRESSURES

Several theories with regard to the origin of high pressures have been postulated by different authors. It will be clear that abnormal high pressures are very much out of equilibrium with their present depth of occurrence. In India, as already stated above, they can be classified in two categories.