Abstract:
Decline curve analysis is an important component in the set of tools used in any reservoir
management plan. Decline curve analysis not only provides current information regarding
the fluid content and the formation characteristics, but also permits a prediction of future
performance.
Decline curve analysis has historically been performed using theoretical models,
whichinvolve production rate , time and cumulative production data from gas reservoirs
and routinely analyzed using dimensionless type curve, which are plots of numerical,
analytical or sometimes empirical solution to gas diffusivity equation. These solutions are
developedtheoretically by coupling the boundary-dominated flow equation with the gas
material balance equation. Due to mathematical difficulty of this process, past efforts
have focused on approximate models based on simplified assumptions such as
approximate linearization schemes for correlating the non-linear viscosity-compressibility
terms and assume production at zero or a constant non-zero bottomhole pressure.These
limitations allow for the development of several semi-analytical expressions for the
analysis of production rate and cumulative production data.
This research proposes a decline curve analysis method based on pseudocumulative
function to gas production data in a boundary dominated gas reservoir. In thesinglephasegas
flow, the use of a pseudocumulative functiongiven as pseudocumulative
production divided by flow rate, allows toobtain a flow equation that has the form of a
harmonic decline. This equationpermits the decline analysis of variable pressure/variable
rate production data; even though early production data are absent for high depleted
reservoir.This method incorporatespseudocumulativefunction that provides a convenient
approach to handle variations in viscosity-compressibilityvalues more rigorously with
pressure since viscosity-compressibility ratio is afunction of cumulative production.The
rate normalized pseudocumulative function does not have any significant effect on
transient behavior. First time, the rate normalized pseudocumulative approach has
successfully been applied indecline curve analysis to both simulated and field data, and,
good results wereobtained.However, this method is strictly valid for boundary-dominated
gas reservoir.
Finally, anew technique has been developed for analyzing gas production data through
decline curve analysis involvinggas production rate, pseudopressure and
pseudocumulativeproduction. This analysis method of gas production data is relatively
easy and the results are compatible with conventional pressure transient
analysis.Therefore, production data analysis should be performed in reservoir engineering
to save time and money for it involves no cost inlost production.This method provide a
level of certainty as regardthe accuracy and quicker estimation of initial-gas-in-place,
reservoir properties, particularly for field data and should enhance the ability of the
engineer to perform reliable analysis.
