Abstract
Vertical and horizontal permeabilities are important parameters for designing well completion and predicting well performance. In the past, to determine the permeabilities from a vertical interference test, some investigators proposed correlations or type curves based on simplified point source solutions. However, it is impossible for these correlations or type curves to cover the variety of scenarios found in the real world. In the recent years, people start to use regression analysis to match the responses at the source interval and the observation point. With regression analysis, we face the problem of non-unique solutions. Sometimes, an estimated permeability is outside a reasonable range when analyzing noisy data from real tests.
In a wireline vertical interference test, we perform a drawdown test followed by a buildup test. Because of the delay of response, the pressure at the observation probe continues to drop for some time during the buildup period at the source interval. The maximum pressure drop at the observation probe with regard to the maximum pressure drop in the source interval is time-delayed. Using this time delay and the maximum pressure drop at the observation probe, we developed a new technique to estimate vertical and horizontal permeabilities based on the line source solutions. We have also worked out a novel numerical scheme. The new technique is compared with the previous methods and shows its superiority in accuracy. In addition, our technique can be used in any situation with different test configurations. Application issues in real testing conditions are discussed. Finally, two field tests are analyzed using this technique. Previously, these tests could not be analyzed to determine vertical permeability using published methods because of the poor data quality.
