The main objective of this paper is to design a new well test that will unable us to determine the individual layer properties (layer permeability, layer porosity, layer diffusivity and layer skin) early in the life of the reservoir, taking into considerations cost, time and the environmental impact of well testing. The pre-production well test is a well test that is carried early in the life of the reservoirs when the information is most needed for planning production schedule and economic decisions concerning the life of the wells. Pre-production is the period after completion but before production of the well. Directly after perforations, we position a pressure gauge above the top perforation to measure the pressure performance from the total system (two or three layer systems). Cross flow in the wellbore from one layer to another will cause the pressure signal. The cross flow is due to the differential pressure between the layers. One important advantage of the pre-production well test is that there is no production on surface during the test. Thus, the environmental impact caused by flaring oil or gas during a conventional well test is all eviated.

In this paper we developed a general mathematical solution to model the reservoir performance of commingled reservoirs with unequal initial pressures in Laplace space. The reservoir performance information available from this model includes wellbore pressures, layer sandface flowrates and layer cumulative production.

The computational solutions developed are used to model the reservoir performance for two layered and three layered cases from the literature. The results are verified by comparing them to the results generated using a finite-difference simulator. The agreement was found to be excellent for all the tested cases.

We developed the "Derivative Extreme Method" (DEM) for the analysis of the wellbore pressure measured during the pre-production well test. The DEM determines layer properties from early and middle time region data. Thus, well testing time is reduced.

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