This paper will investigate utilizing borehole acoustic logs to predict pore pressure at the borehole and how can we infer pore pressure from velocity logs. We will review common approaches to predict pore pressure at the borehole using acoustic logs. Two specific velocity to effective pressure equations will be the focus of this study: Eaton’s equation (citation not found: eaton:aa) and Bower’s equation (citation not found: bowers1995pore). We will discuss the normal compaction trend analysis and how it could help identify overpressure zones using Eaton’s equation. In conclusion, we aim to examine the advantages and disadvantages of those methods. This paper will provide a contribution in advocating the use of borehole acoustics to infer pressure at the borehole in the absence of direct pressure measurement.
There are several reasons behind abnormal pressure; this paper intends to focus on borehole method that could predict pressure caused by undercompaction. Undercompaction occurs when the rates of deposition and burial are higher compared to relative vertical permeability of the sediments; hence, trapping the fluid within those pores as the fluid would not able to escape. Trapped fluid inability escape to maintain the hydrostatic pressure will cause an increase in pore pressure (Bruce 2002).
Undercompaction is considered the major reason behind overpressure build-up in the GOM (citation not found: dickinson1953geological),(citation not found: hubbert1959role). Pressure is a fluid property caused by specific geological conditions. Therefore, we must honor the geological settings in our analysis. A geological understanding of the depositional history could pinpoint to the depositional trend. NCT analysis has been proven capable of identifying undercompaction in the GOM (citation not found: magara1978compaction).