Chapter 28 - Conclusions

Abstract

This chapter presents methodology for detection of increased danger of upward gas migration and surface gas leakage, due to oil and gas production and variation in time of seismic–tectonic processes. Formulation of new earthquake precursors directly linked to current seismic–tectonic activity in the area of oil and gas production, based not only on variations in seismic activity, but on the analysis of environmental phenomena related to oil production. Increase in gas leakage and gas concentration in soils indicates the formation of vertically and subvertically oriented fractures over oilfields, which may be caused by reservoir compaction and consequent ground subsidence. When encountering faults and fractured zones, this free gas may migrate toward the surface. Even small seismic disturbances of oil and gas production can cause environmental disasters, such as subsidence, earthquakes, and gas explosions. Gas or water injection can also result in fracturing of the subsurface formations due to overpressurizing the formations and earthquakes. Fractures in rocks over producing petroleum reservoirs form due to: tectonic and digenetic history, current tectonic and seismo-tectonic movements, and deformations caused by compaction of reservoir rocks. In reservoirs that are divided into independent fault blocks, stresses at the boundary zones of adjacent blocks, increased by the injected fluids, can become high enough to cause massive fracturing of the rocks. In seismically active areas, the increased upward gas migration can become a major environmental hazard.