The estimation of resource includes all possible accumulation of oil & gas on the basis of the size, value of the reserves and the quality of oil & gas. The two interrelated studies are qualitative and quantitative estimation. The qualitative estimation reflects the geological model of the area and identified spatial variation of geological factors, favourable for generation and accumulation of hydrocarbons.

The quantitative prognosis is an expression of theoretical knowledge and observed pattern with the help of parameters which can be measured, collected and systematized. The distribution of hydrocarbon resources in the sedimentary basins is a fundamental requirement to plan the rationale of exploration and conversion of the resources into in-place hydrocarbon in future. However they provide an order of magnitude of estimate of potential, which is accurate enough to allow resource planning, and rational investment decisions.

The estimation of prognostic resources is based on the results of generalization of geological, geophysical, geochemical and hydro-geological investigations as well as on analogy of studied fields within the limits of the area under estimation with help of methods like William W. Mallory (1975) method and R.W. Jones (1975) factor model. Reserve estimation techniques include volumetric, material balance, decline curve analysis, simulation studies and geophysical techniques.

Inputs for CBM initially in place (CIIP) estimation include geological parameters, coal bed methane (CBM) specific parameters and the production history. CIIP will be classified as Proved and Unproved categories. The Unproved portion will further be classified as Probable and Possible categories. Reserve and Resource estimates are inherently uncertain. The classification system and the reporting standards differ widely. There is no universally accepted global standard. But SPE, WPC and AAPG definitions are most widely in use. UNFC a flexible framework that is possibly consistent with SPE, WPC and AAPG.

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