Abstract
The concept of radius of investigation (ROI) has been very useful in assessing the sampled volumes of reservoirs while running well tests. This is also helpful in assessing the (pressure) stabilization times of hydrocarbon units, determining draining areas, and estimating hydrocarbon reserves. Dozens of analytical formulas that are available in the literature have been dedicated to homogeneous reservoirs. However, not much has been reported on the efforts to understand how the ROI concept can be applied to heterogeneous reservoir systems. This study presents a new approach with profiling pressure-derivative values with time in heterogeneous systems to estimate the ROI.
The relationship between the reservoir permeability and the well-test derivative of the pressures measured at the wellbore has already been understood. We will introduce a similar concept to calculate the derivatives at different radial points inside the reservoir for a progressive sequence of elapsed times. By studying the profiles of the derivative values, it is possible to determine how deep the extent of the ROI is. We will also demonstrate that there exists a relationship at a given time between the derivative values at the wellbore and those inside the reservoir.
