A graphical plot of pressure versus time during pressure build-up in a temporarily closed well is matched to a type-curve on a graph of such curves to determine if the well is fractured, acidified, fissured or damaged.

Method for performing step rate tests on injection wells, including inserting a portable pumping unit to receive the water or other fluid normally injected into the well and controlling its pressure, and then increasing the pressure of the injection fluid to a predetermined pressure by use of the portable pumping unit to determine fluid flow at said predetermined pressure, the fluid at the predetermined pressure being pumped continuously until a stable flow rate is achieved. The procedure is repeated for plural stepwisely increased pressure points at each side of the fracture pressure, whereby the fracture pressure is accurately determined.

A method for determining desired physical characteristics of an underground formation is provided. The present invention is characterized by a determination of dimensionless pressure parameters without resort to a series of type-curves. The method includes finding a pressure match that relates a dimensionless function of pressure with experimental pressure data and finding a time match that relates a dimensionless function of time with dimensioned time. In one embodiment, this determination is made using a pressure derivative curve plotted on a computer terminal display screen. An interactive graphics software package is utilized in which the user selects certain values associated with the experimental data for which corresponding dimensionless values are known. From the determined values of pressure match and time match, a dimensionless function of pressure curve and a dimensionless pressure function derivative curve are provided on the display screen. Type-curves represented by dimensionless parameters are also provided. A selection of an appropriate interpretation model is made using the experimental pressure function curve and one of the series of type-curves. From the selection, the user is able to determine the physical characteristics of the underground formation.

The invention relates to a well test method for determining the physical characteristics of a system made up of a well and a subsurface formation containing a fluid such as a hydrocarbon. A change in the flow rate of said fluid is produced for a short period (duration t.sub.P of the order of a few minutes) so as to obtain a flow pulse resembling a Dirac pulse; the variations .DELTA.P of the down-hole fluid pressure is measured during said short period and then during the subsequent period of return to the initial state of the well-formation system, and the experimental pressure curve thus obtained is compared with the curves of a double network of type curves representing, as a function of a common parameter, the pressure P.sub.D and its derivative P'.sub.D with respect to time, by matching the branch of the experimental curve corresponding to the short period with a curve P.sub.D and the branch of this curve corresponding to the subsequent period with the curve P'.sub.D of the same parameter.

The matrix treatment of a subterranean formation is adjusted in real time to minimize formation damage as indicated by the skin factor. The process comprises initial injecting an inert fluid into the formation and observing the variation in injection pressure over time. During the matrix treatment with a treatment fluid, the pressure is again observed over time and, by comparison with the pressure variation noted in the inert fluid injection phase, the skin factor is determined. The treatment parameters are then adjusted in real time to minimize the skin factor thereby minimizing formation damage.