Perpustakaan Digital ITB

Overpressure studies have had a huge impact on drilling safety and the economics of drilling design and well construction. The main objective of this project is to generate a pressure map derived from the seismic velocity. The problem for this project is there is no well with normal pressure, so it's hard to find the benchmark for normal velocity, and also to calibrate with the calculated data. Overpressure is a pore pressure that abnormally high, exceeding the hydrostatic pressure at given depth. Overpressure can be detected in area with the high mudweight measurement and low velocity. The first way to indicate the overpressure zone, we can simply make a pressure plot, which is just a pressure data that plotted versus the depth point, together with the hydrostatic pressure and lithostatic pressure. Points that exceed the hydrostatic curve can be assumed as overpressure zone. After confirming all with the well report, pick the horizon in the seismic in order to calculate the interval velocity using Dix equation. The interval velocity are neede to find the threshold velocity.In order to find the threshold velocity we use an empirical way which is plot the stacking velocity versus their two-way time. Get a ratio between the normal velocity and the velocity affected with overpressure, and apply it as % increases to the velocity normal calculated earlier using Dix equation.To generate a pressure map, we need to transform the velocity to pressure using Eaton ratio method. Eaton ratio method is typically applied to seismic. The procedure is to examine the pore pressure versus the depth data and to make a ratio comparison between the velocity value recorded and the expected value.