Abnormal Formation Pressures

This book studies the mechanisms and causes of abnormal pressure distribution while drilling.

When Fertl's first book, Abnormal Formation Pressures, was published by Elsevier in 1976, the topic was relatively new in book form. In the years that followed, his book became the standard work for petroleum engineers and drillers. The list of major petroleum provinces with abnormally high pore pressures has grown steadily over the years, and with it has grown our knowledge and experience. There have also been technological advances. A new book was required, but no longer could the topic be covered adequately by one person. The problems of abnormally high formation pressures encountered in the subsurface while drilling for petroleum are very diverse, involving geologists, geophysicists, reservoir engineers, drilling engineers, and borehole logging engineers. The acute anticipation of such pressures before drilling has become possible with modern technology. This book treats these developments and covers the following topics: world occurrences, the geology of abnormal pore pressures and the background theory, reservoir engineering aspects of abnormally pressured reservoirs, detection of abnormal pressures by geophysical methods before drilling and during drilling, and their evaluation after drilling. It examines the special problems of shallow hazards from shallow abnormal pressures, and relief-well engineering to control blowouts. It also examines the generation of abnormal pressures from hydrocarbon generation in the Rocky Mountains, and the distribution of abnormal pressures in south Louisiana, USA. The topics are examined from a practical point of view with a theoretical background. There is a glossary of terms, and a relevant practical conversion table. Both SI units and the conventional US oil industry units are used.

This book discusses how sediments compact with depth and applications of the compaction trends. Porosity reduction in sediment conveniently indicates the degree of sediments compacted after deposition. Published empirical curves- the compaction curves- are depth-wise porosity variation through which change in pore spaces from sediment surface to deeper depths e.g. up to 6 km can be delineated. Porosity is derived from well logs. Compaction curves, referred to as the Normal Porosity Profile of shales, sandstones and shale bearing sandstones of different models are reviewed along with the different mechanical and chemical compaction processes. These compaction models reveals how porosity reduces depth-wise and the probable reason for anomalous zones. Deviation from these normal compaction trends may indicate abnormal pressure scenarios: either over- or under pressure. We highlight global examples of abnormal pressure scenarios along with the different primary- and secondary mechanisms. Well logs and cores being the direct measurements of porosity, well log is the only cost-effective way to determine porosity of subsurface rocks. Certain well logs can detect overpressure and the preference of one log above the other helps reduce the uncertainty. Apart from delineation of under-compacted zones by comparing the modeled- with the actual compaction, porosity data can also estimate erosion.

Knowledge of the presence of abnormally-high pressure zones (AHFP) prior to drilling into them can prevent considerable economic losses and, possibly, save human lives. The various origins (undercompaction, tectonics, etc.) of AHFPs are discussed, followed by the description of predictive techniques in clastic, carbonate and salt-bearing formations. In addition to the well-logging predictive techniques, the authors discuss smectite-illite transformation and the chemistry of interstitial solutions. Other topics covered include (a) abnormally low formation pressures and subsidence, and (b) mathematical modelling. Loss of potential production may result if AHFPs are not properly identified and evaluated. Many hydrocarbon-bearing formations with AHFPs are erroneously "condemned".This book is of interest to engineers and geologists involved in the (a) evaluation, (b) drilling in, (c) completing, and (d) producing from hydrocarbon reservoirs with AHFPs.