Theoretical Justifications For Rate Decline Trends In Solution-Gas Drive Reservoirs, And Reservoir Property Estimation Using Production Data

ABSTRACT

Rate decline analysis is an essential tool in predicting reservoir performance and formation

property estimation. The use of historical production data to predict future performance is

the focus of the empirical domain of decline analysis while the theoretical domain focuses

on the use of such data to estimate formation properties.

A number of attempts have been made to establish the theories of rate decline in solutiongas

drive reservoirs. Such attempts have established the theoretical decline exponent b as a

function of formation properties. However, none of the attempts have established a direct

link between the empirical and theoretical domains of decline analysis. The purpose of this

work is to establish the missing link and deploy such link in reservoir property estimation.

In this work, a functional relationship (equation) between the empirical (___ ) and the

theoretical (___) was derived; based on the definition of a new parameter known as timeweighted

average of the theoretical exponent, ___ . This new parameter was found to be

related to the empirical exponent, ___     thus establishing the link. Theoretical justifications

for the ranges of values of the theoretical exponent were also offered. Consequent upon the

establishment of the relationship, this work developed a new improved technique for

estimating reservoir permeability. The technique was applied to a number of cases and was

found to yield excellent estimates of permeability even for an heterogeneous reservoir.

Sensitivity analyses were performed on the results. The work also investigated non-Darcy

flow effects on decline parameters. Lastly, this work provided mathematical justification for the existence of the hyperbolic family of curves in solution-gas drive reservoirs.