Seal Failure Related to Basin-scale Processes
The leakage of trapped petroleum is a major concern in hydrocarbon exploration and has led to a large number of exploration failures. Changes in stress state, fluid pressure, and cap rock permeability may all result in a loss of trapped hydrocarbons. Such changes may result from several different subsurface processes.
This chapter describes an examination of important processes that control compaction, fluid flow in reservoirs, fault reactivation, and their influence on leakage from hydrocarbon reservoirs. It was concluded that seal-failure analysis is seldom based on more than a few of the operating processes and therefore does not reach its full potential. Especially, the effects of overpressures on sediment compaction and hydrocarbon leakage seem to have been oversimplified and commonly overstated. The conditions for hydrofracturing and the corresponding loss of hydrocarbons from structural crests are also commonly considered too superficially in sealing analyses.
It was concluded that inadequate leakage assessments can result from neglect of some subsurface processes that influence stress, pore pressure, and hydrocarbon permeability in the seal. Seal integrity predictions can be improved if thorough analyses of the relevant subsurface processes routinely precede the sealing analyses.
Figures & Tables
This volume constitutes the proceedings of the AAPG Hedberg conference on seals held in Barossa Valley, South Australia, in 2002. The key driver for both the Hedberg conference and this publication was the recognition that knowledge of risk in the estimation of sealing capacity and fault-seal potential is important in making judgments at the exploration, appraisal, and development stages of the petroleum business. In addition, incorporating seal risk in the overall assessment of hydrocarbons in place can affect decisions to drill prospects and the location of appraisal and development wells, as well as reserve estimation. Improved methods to estimate seal capacity and fault integrity can lead to savings in well costs, improved recoveries through optimum placement of wells, and improved estimates of hydrocarbon in place. This volume contains 18 chapters that reflect the spectrum of presentations at the conference. The knowledge imparted by these chapters will be a window on the state of seal knowledge at this juncture of time and includes topics such as seal failure related to basin-scale processes, the role of geomechanics in seals, and the economic evaluation of prospects with a top seal risk.