Virtually all oil and gas-bearing rocks are sedimentary in origin The dominantly fragmental sediments are subdivided according to textural considerations inta conglomerates, sandstones, siltstones, and shales or mudstones. Of these materials, sandstones are the most important reservoir rock material.Using waterflooding experiments mercury porosimetry, and spectro-electromicroscope techniques, some features and important properties of Berea sandstone rocks were determined.
The analysis indicated that carbonate and quartz overgrowth were the types of cement present. The average wettability index was found to be related to the amounts and types of cements. Moreover, an inverse proportionality relationship appears to relate the wetttability index to the amounts and types of cement present.Wettability is also affected by the amounts of day matrix in the investigated cores. We concluded mat a large amount of clays reduces the welling phase affinity to Berea sandstone rock matrix.
Porosity, a rock property, was also found to be a function of the amounts of clay matrix. In Berea sandstone rocks, total porosity variations depend on the variation of the primary porosity. Total porosity is nor proportional to secondary porosity. Secondary porosity is invariant with variable total porosity range. This same conclusion can also be said abut the amounts of framework grains comprising the Berea sandstone Cores. Porosity is also found to be a function of the amounts of cements in Berea. High amounts of carbonate cements reduce total porosity. The amounts of quartz overgrowth affect the total porosity as well. It was concluded that higher amounts of quartz overgrowth reduce total porosity drastically. Besides residual oil saturation in Berea sandstone rocks is proportional to the rock total porosity. This is mainly 3rcributed to the nature of fluid flow which is controlled by capillary forces.
Tortuosity values expressed in terms of the wetting phase retention time are a function of the amounts of carbonate cement and quartz overgrowth. Tortuosity is found to be inversely proportional 10 the amounts of carbonate cement and quartz overgrowth in Berea cores.
Further analysis indicated that the average rock surface area available to the non-wetting phase is dependent on the amounts of clay matrix, carbonate cement and the amounts of quartz overgrowth in Berea rocks.
Effective displacement of oil from the formation is influenced by the degree of continuity and uniformity of the producing formation. In determining the mechanisms by which oil is recovered by a secondary recovery method (such as waterflooding), macroscopic properties influencing such recoveries are nor sufficient to fully understand oil recovery mechanisms.
To simulate actual fluid flow mechanisms in strongly water-wet systems where capillary forces are the predominant driving mechanisms, a low average frontal advance rate of one fool/day was selected. As a result, the ratio of capillary to viscous forces was equal to 1.344x10−7. In such situations, reservoir rock producibility depends to a large extent on the size, shape, arrangement and distribution of pores and also rock porosity, surface area and wettability.
Besides, lithofacies distribution and diagenetic history, porosity origin, surface area and wettability permit better assessment of oil recovery.
