Pore network modeling: A route to improved reservoir quality assessment in Arabian reservoirs. 9th Middle East Geosciences Conference, GEO 2010.

Abstract

Frequently in reservoir quality assessment, it is that which is not easily seen which has the biggest impact on fluid-flow behavior. The work presented here looks at the problems of quantifying two very different reservoirs, the carbonates of the Jurassic Arab-D Reservoir and the clastics of the Devonian Jauf Formation, both of which are impacted by pore system attributes beyond the resolution of a standard optical microscope. We highlight the results of the 3-D pore network modeling on these samples, contrasting this with the conventional approach to porosity and permeability calculation. Studies of the Arab-D reservoirs in Saudi Arabia highlight the importance of microporosity as a significant factor affecting porosity-permeability transforms. Generally, such pores are less than 10 microns in size, but can account for over 50% of the pore volume in a sample. The more microporosity, the greater is the deviation away from the average porosity-permeability trend. Modeling of the pore network in clastics of the Jauf Formation is complicated by the texture and mineralogy of the sandstones. The grains are often covered with a thin layer of illite, comprising flakes which are oriented radially to the grain surface. High microporosity within this layer and the thin nature of the flakes results in a diffuse layer around each grain, lowering the permeability. If we wish to model and predict permeability by transforming porosity data (such as obtained from wireline logs), then it is imperative to know the amount of microporosity. Given the problems of optically imaging microporosity in carbonates and sandstones, coupled with the complexities of a three-dimensional pore system, a 3-D modeling tool was used to capture and model these samples. Thin sections and scanning electron microscope images from the samples were studied statistically in 2-D and then the characteristics of the grains were reproduced in 3-D replicating the depositional mode of the grains, their compaction and diagenesis. An algorithm for pore network extraction then built a topologically-equivalent network consisting of balls representing the pore bodies and cylindrical segments representing pore throats. Porosity and permeabilities were obtained by calculating the proportion of voids space and by applying a pore flow code using elementary mechanisms of pore filling. Additionally, the Lattice Boltzmann Method has also been used to calculate pore flow inside the 3-D image itself.