Excessive Pressures and Pressure Variations with Depth of Petroleum Reservoirs in the Gulf Coast Region of Texas and Louisiana

Abstract

This paper discusses the results of a study of reservoir pressures in theGulf Coast area of Texas and Louisiana, showing the general relation of thereservoir pressure to its subsea depth, as well as excessive reservoirpressures that have been encountered. The latter are particularly important inmud-control work, and the data show why it is necessary to use muds having arelatively high density in many of the deeper wells drilled in this area. Onlya comparatively few of the wells drilled in the Gulf Coast that haveencountered excessive pressures are discussed, but as far as is known thoseomitted fall within the range of pressure observed by the writers. Measurement of Pressures The following methods were used to determine the values of the originalpressures:Estimation of original pressure from subsequent pressure behavior of fields.This method is not precise, and was used only in a few of the older fields inwhich better methods of obtaining original pressures were not available. Onlynormal pressures were determined by this method.Measurement of shut-in pressures soon after completion of the firstproducing well. With one exception, all pressures measured by this method werenormal, this well having a pressure slightly higher than normal.Measurements of pressure in connection with drill-stem tests.Estimates from the maximum hydrostatic head of mud that failed to preventflow from the high-pressure formations into the hole. This method is not exact, tending generally to indicate low pressures. Normal Pressures All pressure measurements available are plotted in Fig. 1, with originalpressure at the water-oil contact as abscissa and subsea depth as ordinate.