A new method for bulk palynological processing of oil-contaminated chalks

Abstract. INTRODUCTION

The application of palynomorphs in well-site dating and correlation within the Upper Cretaceous—Danian Chalk Group of the North Sea, is currently being investigated at the Geological Survey of Denmark. Due to the relatively low abundance of palynomorphs in the chalks, a large sample size (100–300g) is often needed to obtain representative microfloras. Palynological preparation of large chalk samples does, however, create processing problems, especially if the samples derive from oil bearing intervals. The aim of this note is to describe a method developed at the Geological Survey of Denmark to overcome these processing problems.

PROBLEMS IN THE PREPARATION OF LARGE CHALK SAMPLES.

The problems during the preparation process comprise the following factors: The dissolution of carbonates from 100—300g sized chalk samples with hydrochloric acid causes a vigorous reaction that developes vast amounts of foam. The foam development is usually controlled by spraying alcohol or the more hazardous acetone into the reaction vessel; these solvents reduce the vigorous expansion of the foam by reducing the surface tension of the acid. This procedure, however, demands constant surveillance of the acid treatment, because the effect of the solvents is of short duration. Furthermore, the initial vigorous reaction restricts the use of stronger, more effective hydrofluoric acid concentrations to later parts of the acid treatment process, where the reaction is more calm. In the Danish sector of the North Sea, the main producing reservoir is situated in the Chalk Group. Core samples from the Chalk Group are therefore usually usually oil bearing . . .