The resource assessment of unconventional gas accumulations depends on C B"C C conventionalC B"C C methods including the reconstruction of the tectonosedimentary evolution of the given basin, the organic content, the understanding of the subsidence, burial, thermal and maturation history, and the timing and mechanism of hydrocarbon generation. In addition, successful production strategies should rely on "unconventional" approaches. The long path from recognizing the potential to the actual production of such hydrocarbon systems requires understanding fluid flow mechanism in nanoporous rock matrix. It is recognized that Darcy permeability is of limited use when applied to tight rocks with unperturbed, non-fractured, nano-range pore size where the pressure gradient would not enable gas flow. Instead, concentration-driven diffusion as a function of the fracced rock mass surface has critical importance. This process has been recently identified as the main driving force of fluid flow in extremely tight rocks. Besides optimizing production technologies, such as various stimulation techniques, they critically influence reserve estimations through highly uncertain recovery, a key to the ultimate economic assessment of unconventional projects. Experience shows that, when diffusion flow dominates in the rock matrix, even the latest pressure pulse decay permeability test equipment may be insufficient to describe the process. The use of photo-acoustic laser apparatus to measure mass flow is an efficient tool of has enabled resource estimation and proved very helpful in the engineering of frac operations. New laboratory measurements reported in our presentation enables to determine diffusion coefficient under realistic HP-HT and various sorption/desorption conditions, hence allowing production simulation. Case study from the MakC C B3 Trough in the Pannonian basin, Hungary, shows the great potential of this novel methodology. The definition of diffusion characteristics can be used as an aquifer protection technique in conjunction with the stimulation engineering.

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