Application of a stochastic network pore model to oil-bearing rock with observations relevant to oil recovery

Mercury porosimeter experiments have been traditionally used to investigate the pore structure of oil bearing rocks, although interpretation based upon the oversimplified parallel-bundle model is inadequate to explain many practical aspects of oil recovery. A technique for stochastically assigning the sizes of tubular pore segments placed in a network configuration of interconnected pores has been used to model pore structure and a trial and erro procedure has been devised which gives directly the size distribution of segments comprising the network which will exactly reproduce any observed merc porosimeter penetration curve. The theory is applied to porosimeter tests on a core sample from the Agha Jari Field (Iran). It is evident that the pore distribution function according to a network interpretation comprises a very much greater proportion of larger pores than is inferred from the parallel model. This distortion of the pore size distribution is shown to arise from the inaccessibility of larger segments when surrounded by small pores, a phenomenon that cannot be represented by the parallel-bundle approach. As a quantified interconnecting pore model, the network analysis has potential for investigating oil retention mechanisms in a reservoir, and the probable micro-scale water displacement behaviour of the pore network deduced to rep the core sample is described. Low recovery factors seem to be related to water flowing preferentially through pathways made of larger pores. Entrapment likely in large pores isolated by surrounding smaller ones.