EVALUATING THE VOLUME OF POROUS-MEDIUM INVESTIGATED DURING SLUG TESTS

This paper presents a methodology for quantifying the volume of porous medium investigated during a slug test in an unbounded porous medium, in the presence of a linear constant-head or no-flow boundary, and in the presence of a radial no-flow boundary. For the unbounded case, ty pe curves are generated for different values of the wellbore storage c oefficient, which relate the distance travelled by a given pressure pe rturbation (1, 5, and 10% of the initial drawdown in the well), to dim ensionless time. This distance is found to increase linearly on a log- log plot until it reaches a maximum which is a function of the wellbor e storage coefficient. The appropriate choice of dimensionless groups allows the different curves for each level of perturbation to be colla psed into one curve. Functional relationships offer an alternative to using the type curves graphically. For bounded systems, type curves re late the distance to the boundary to the time of 1 and 5% deviation fr om the unbounded response. Although these curves cannot be collapsed, the presented range of wellbore storage coefficients covers most pract ical situations. Developed relationships allow the estimation of the m aximum distance travelled by the pressure perturbations in the unbound ed case, and the maximum distance at which a linear constant-head or n o-flow boundary, or a radial no-flow boundary, still produces a given deviation in the pressure response measured at the well. An applicatio n shows that substantial error may result if the distance to a boundar y is evaluated while neglecting storage in the well. Finally, applicat ion of the methodology developed for a linear no-flow boundary to a re al data set yields a realistic distance to the boundary and a far bett er match between simulated and measured data than if an unbounded syst em is considered. The type curves and relationships presented here sho uld be applicable to slug test design and analysis.