EFFECTS OF SOME SIMPLIFYING ASSUMPTIONS ON INTERPRETATION OF TRANSIENT DATA

Fluid low in porous media is described by the diffusional type of part ial differential equation. In deriving the flow equation for the const ant compressibility fluids, an important assumption is made regarding the magnitude of the pressure gradient is assumed that this gradient i s small enough that the square of this term becomes negligible. In thi s study, an attempt is made to quantify the effect of this simplificat ion. Data generated by numerical simulator and analytical solutions ar e compared in order to determine the conditions under which this simpl ification is justified. Except for extreme conditions (non-linear coef ficient greater than 0.01), in is justifiable to ignore the square of the pressure gradient term in oil diffusional equation. The drawdown s olution on gas wells contains gas properties, which are pressure depen dent. As the system is being depleted. the average reservoir pressure declines. Although it seems logical to consider the gas properties at the prevailing reservoir pressure, the gas viscosity and compressibili ty are usually evaluated at the initial pressure level. Comparison of the analytical solutions with numerical solutions obtained for a varie ty or typical well rest conditions indicates the magnitude of inaccura cy incurred by using standard approach to data interpretation. Based o n this investigation, several pressure levels for properties calculati on are considered. In applying analytical equations for pseudo-steady state flow conditions, gas properties should be evaluated at an averag e value of the initial and current reservoir pressures.