An approach for estimating porosity from sonic-logs in shaly formations

Abstract EN

The determination of bulk volume water (BVW) and hydrocarbon (BVHC) involve the determination of effective porosity (φ).

Log analysts evaluate porosity either from core measurements or analysis of porosity tools (density ; ρb, neutron ; φN, and acoustic ; Δt).

In the absence of core measurements, much useful information about porosity can be known by using a combination of at least two of these logs.

The lack of these porosity tools makes the determination of porosity difficult.

At present, there are several equations for computing porosity from sonic transit time ; the most common available log in the wells and formations.

An equation for estimating effective porosity values from sonic and a gamma ray (GR) log was established for different lithologies.

Based on the reformulation of a certain known equation, it is essential to apply it in a shaly formation.

This equation yields good porosity values when compared with the actual porosity existing in the same field.

The mechanism of this equation and the results obtained, are illustrated by field example.