ABSTRACT

Recent years have seen a continuing increase in the practice of obtaining formation samples through the use of percussion type side wall coring tools. Concurrently with this increase, analytical methods have improved to the point where it is now possible to make quantitative measurements of the physical properties of the samples with a very satisfactory degree of precision. It has long been recognized, however, that the quantitative data thus obtained differ significantly from those obtained by analysis of wire line or conventional cores. In order to resolve some of the differences which were apparent, a study was undertaken utilizing electronic data processing equipment on selected groups of both side wall and conventional type core data from the Miocene, Frio, and Yegua formations. Data from a total of 5338 samples were employed in the study. It was determined that side wall sample permeabilities are increased in low permeability formations and decreased in higher permeability formations. The total water saturations of the side wall cores can be expected to be higher than data obtained from corresponding conventional type cores. The oil saturations are only slightly lower in the side wall cores and the difference is not significant.

Other factors contributing to difficulty in side wall data interpretation were investigated. Increased frequency of sampling and proper handling of side wall cores are suggested as means of improving the utility of the data obtained by core analysis. The electric log is considered to be a necessary part of the analytical procedure and should accompany any samples submitted for analysis.