ABSTRACT
In this paper, the radial and linear flow regimes in long, narrow channels were studied. The extent and duration of each regime was noted for a number of different dimensionless channel widths. Both "semilog" and "square root time" plots were made of the pressure transient behavior at the wellbore. These plots, as expected, showed radial flow (semilog straight line) at the beginning and linear flow (square root straight line) at later times. An abrupt change from radial to linear flow does not occur, rather there is a region where the pressure transient behavior closely approximates radial and linear flow at the same time.
An equation was derived for calculating the channel width, using the time where the semilog straight line ends. The linear flow regime in long, narrow channels can be precisely analyzed using existing linear flow equations, with the incorporation of a "pseudo-skin" factor, which accounts for the additional pressure drop due to the decreasing crosssectional area for flow as flowlines converge at the wellbore. Because of this additional "pseudo-skin" factor, log-log plots of the pressure transient behavior of long, narrow channels do not yield lines of slope one half (until time becomes very large), and hence these plots, which are often used to detect linear flow, should not be used.
The practical implications of this study are discussed as they pertain to production and drillstem tests. It appears that the end of the semilog straight line and the beginning of linear flow can be detected during the time that a drillstem test is conducted.
