Estimating reservoir size without 3D Seismic involves estimating the bulk volume of the reservoir using well logs, core data, well test data, and 2-dimensional seismic data. A reservoir engineer uses this data to create contour and isopach maps of the reservoir. The 2D seismic provides the footprint of the reservoir while well logs are used to determine formation thickness. The core data is used to determine the porosity of the rock. Well test data can be used in a history match to fine tune the assumptions.
Here’s how it works:
A subsurface contour map shows lines connecting points of equal elevations on the top of a marker bed and therefore shows geologic structure. A net isopach map shows lines connecting points of equal net formation thickness; and the individual lines connecting points of equal thickness are called isopach lines. The contour map is used in preparing the isopach maps when there is an oil-water, gas-water, or gas-oil contact. The contact line is the zero isopach line. The volume is obtained by planimetering the areas between the isopach lines of the entire reservoir or of the individual units under consideration. The principal problems in preparing a map of this type are the proper interpretation of net sand thickness from the well logs and the outlining of the productive area of the field as defined by the fluid contacts, faults, or permeability barriers on the subsurface contour map.