摘要
Drilling into a geopressured zone will generally cause a change in a number of basic formation/ drilling relationships. This change is usually seen as a reversal of a gradual depth related trend in a lithologically uniform formation. Of all the geophysical methods, the reflection seismic method is essentially the only technique used to predict pore pressures. The seismic method detects changes of interval velocity with depth from velocity analysis of the seismic data. These changes are in turn related to lithology, pore fluid type, rock fracturing and pressure changes within a stratigraphic column. When the factors affecting the velocity are understood for a given area, a successful pressure prediction can be made. For clastic environments such as the Tertiary section of the Gulf of Mexico or the Niger delta, the interval velocity of the rocks increases with depth because of compaction. In these areas, deviations from normal compaction trends are related to abnormally high pore pressures. The adapted methods provide a much easier way to handle normal compaction trend lines. In addition to well log methods, pressure detection can be obtained via drilling parameters by applying Eaton’s DXC methods. Seismic velocities have long been used to estimate pore pressure, indeed both these quantities are influenced by variations in rock properties such as porosity, density, effective stress and so on, and high pore pressure zones are often associated with low seismic velocities. Pressure prediction from seismic data is based on fundamentals of rock physics and seismic attribute analysis. This paper hence tries to assess the use of seismic waves as a viable means to calculate pore pressure, especially in areas where no prior drilling history can be found. Then we applied these methods on LAGIA-8 well, Sinai, Egypt as a case study. Pore pressure prediction from Seismic is a very essential tool to predict pore pressure before drilling operation. This could prevent the well problem as well blowout and to prevent formation damage, especially in areas where no prior drilling history can be found.
Drilling into a geopressured zone will generally cause a change in a number of basic formation/ drilling relationships. This change is usually seen as a reversal of a gradual depth related trend in a lithologically uniform formation. Of all the geophysical methods, the reflection seismic method is essentially the only technique used to predict pore pressures. The seismic method detects changes of interval velocity with depth from velocity analysis of the seismic data. These changes are in turn related to lithology, pore fluid type, rock fracturing and pressure changes within a stratigraphic column. When the factors affecting the velocity are understood for a given area, a successful pressure prediction can be made. For clastic environments such as the Tertiary section of the Gulf of Mexico or the Niger delta, the interval velocity of the rocks increases with depth because of compaction. In these areas, deviations from normal compaction trends are related to abnormally high pore pressures. The adapted methods provide a much easier way to handle normal compaction trend lines. In addition to well log methods, pressure detection can be obtained via drilling parameters by applying Eaton’s DXC methods. Seismic velocities have long been used to estimate pore pressure, indeed both these quantities are influenced by variations in rock properties such as porosity, density, effective stress and so on, and high pore pressure zones are often associated with low seismic velocities. Pressure prediction from seismic data is based on fundamentals of rock physics and seismic attribute analysis. This paper hence tries to assess the use of seismic waves as a viable means to calculate pore pressure, especially in areas where no prior drilling history can be found. Then we applied these methods on LAGIA-8 well, Sinai, Egypt as a case study. Pore pressure prediction from Seismic is a very essential tool to predict pore pressure before drilling operation. This could prevent the well problem as well blowout and to prevent formation damage, especially in areas where no prior drilling history can be found.
作者
Ahmed Zakaria Noah
Ahmed Zakaria Noah(Exploration Department, Egyptian Petroleum Research Institute, Cairo, Egypt)
