eliminates the ambiguity in the Gringarten type curve. The derivative type curve proposed by Bourdet et al. However, adjacent pairs of curves can be quite similar, and this fact can cause uncertainty when trying to match test data to the "uniquely correct" curve.įig. Each different value of C D e 2 s describes a pressure response with a shape different (in theory) from the responses for other values of the parameter. the time function t D/ C D, with a parameter C D e 2 s ( Fig. In the Gringarten type curve, p D is plotted vs. The type curve is also useful to analyze pressure buildup tests and for gas wells. These assumptions indicate that the type curve was developed specifically for drawdown tests in undersaturated oil reservoirs. It is based on a solution to the radial diffusivity equation and the following assumptions: vertical well with constant production rate infinite-acting, homogeneous-acting reservoir single-phase, slightly compressible liquid flowing infinitesimal skin factor (thin "membrane" at production face) and constant wellbore-storage coefficient. presented a type curve, commonly called the Gringarten type curve, that achieved widespread use. Solutions to the diffusivity equation for more realistic reservoir models also include the dimensionless skin factor, s, and wellbore storage coefficient, C D, where This leads to much simpler graphical or tabular presentation of the solution than would direct use of Eq. 1 has the advantage that this solution, p D, to the diffusivity equation can be expressed in terms of a single variable, t D, and single parameter, r D. 2, the definitions of the dimensionless variables are (Variables that when the parameters are expressed in terms of the fundamental units of mass, length, and time, have no dimensions are sometimes said to have dimensions of zero.) 1 can be rewritten in terms of conventional definitions of dimensionless variables. 1, presented in terms of dimensional variables:Įq. To review dimensionless variables, consider the Ei-function solution to the flow equation, Eq. The solutions plotted on type curves are usually presented in terms of dimensionless variables. 4 Differences in drawdown and buildup test type curves.Some control panels can measure the pumping rate, and the start-up technician will verify those readings with the physical measurement. This provides a measurement of the pumping rate. The technician then makes a simple calculation to determine the volume that was pumped over the time interval. The pumps run for a specific amount of time and then a measurement is taken for how far down the water was lowered in the well. The Romtec Utilities start-up technician runs the pumps and measures how much water is pumped over a given time interval. When everything is set up correctly, the draw down test is straightforward. With a filled force main, the head pressure will be consistent for the test. This will lead to an unreliable reading from the draw down test, and it will be difficult to measure if the desired pumping rate for the pump station is reached. With an empty force main, the head conditions will be very unpredictable when the pumps operate. The draw down test is used to measure the pumping rate, and in order for this measurement to be accurate, the force main must be filled. One criterion of design is the desired pumping rate and another is the TDH or Total Dynamic Head conditions. Romtec designs pump stations based on a project specific set of design criteria. In order to complete a draw down test, the force main must be filled with water. The most obvious process is to test the pumps, but the water is also required to fill the force main if it is newly installed. Having the water available onsite is needed for two processes. This step can be as easy as tapping into a nearby fire hydrant, but in most scenarios, water is scheduled to be delivered by truck for the start-up. The first requirement for the draw down test is having water available onsite. This test is an important part of commissioning new lift stations and there are things to consider onsite to complete this test. The draw down test is conducted to measure the pumping rate in order to verify that the pumps will operate at the specified flow requirements. One of these tests is called the draw down test. The role of this technician is to start the pump station for the first time and to test the functionality of the system to make sure it functions per the system design criteria. Romtec Utilities commissions each of its pump stations with a start-up technician.
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