Determining multiple length scales in rocks

Carbonate reservoirs in the Middle East are believed to contain about half of the world's oil(1). The processes of sedimentation and diagenesis produc e in carbonate rocks microporous grains and a wide range of pore sizes, res ulting in a complex spatial distribution of pores and pore connectivity(2). This heterogeneity makes it difficult to determine by conventional techniq ues the characteristic pore-length scales, which control fluid transport pr operties. Here we present a bulk-measurement technique that is non-destruct ive and capable of extracting multiple length scales from carbonate rocks. The technique uses nuclear magnetic resonance to exploit the spatially vary ing magnetic field inside the pore space itself-a 'fingerprint' of the pore structure. We found three primary length scales (1-100 mu m) in the Middle -East carbonate rocks and determined that the pores are well connected and spatially mixed. Such information is critical for reliably estimating the a mount of capillary-bound water in the rock, which is important for efficien t oil production. This method might also be used to complement other techni ques(3-5) for the study of shaly sand reservoirs and compartmentalization i n cells and tissues.