A New Device for Determining Porosity by the Gas-expansion Method

In the calculation of oil and gas reserves by volumetric methods, it isnecessary to know the volume of the reservoir available for the storage of theoil or gas. To obtain this information, a number of methods for determiningboth total and effective porosity of reservoir rocks are used. For thedetermination of the total porosity, or the porosity that considers all of thepore spaces, connected and isolated, the Russell and the Melcher-Nuttingmethods are the best known and most widely used in the petroleum industry.These methods have disadvantages in that they give the total porosity of thesamples and in that the samples are reduced to grain size in the determination.In many sands there may be little or no difference between total and effectiveporosity but in other sands there may be considerable difference between thetwo. For the estimation of oil and gas reserves the effective porosity of thereservoir rock always should be used. Of the methods that have been developed for the determination of theeffective porosity of reservoir rocks, or the porosity that considers onlythose pore spaces that are connected, the best known are the so-called Boyle'slaw and the Washburn-Bunting methods. The Washburn- Bunting method is probablythe most widely used because it gives effective porosity, it is rapid, and theapparatus is inexpensive. This method employs a special porosimeter in whichthe core sample is placed in direct contact with mercury. This method hasdisadvantages in that, as a result of the high vacuum created in the porespaces, mercury is drawn into the openings, making it impossible to use thesample for a check determination and also ruining the sample for any furthertest, such as permeability. The purpose of this paper is to describe anapparatus employing the same principle as the Washburn-Bunting method but sodesigned that the core sample does not come in contact with the mercury in theporosimeter. T.P. 1061