Application of Volumetric, Material Balance and Decline Analysis Methods for Gas Initially in Place Estimation

Initial estimate of GIIP by volumetric method needs to be validated with independent
methods in order to gain confidence. Flowing material balance ( p z vs cumulative
production), Fetkovich type curve and Blasingame type curve matching were used for
verification. When the GIIP estimated by these three methods do not converge to one
another, it yielded uncertainties in the GIIP estimated by many oil and gas operators.
When the GIIP estimated were reasonably close to one another, then operators can
proceed with the development plan as the confidence in getting the GIIP right was
high. A comparison study of these three methods suggested that volumetric method,
material balance, Fetkovich type curve and Blasingame type curve yielded 634 BCF,
585 BCF, 567 BCF and 557 BCF respectively. These three independent methods have
been tested with real field data and the results were close enough. With only
differences of 7%, 11% and 12 % from the volumetric method, the results were within
the limits of 14% and the confidence of initial estimate was high.