Summary of Experience with Pressure Coring
Authors: Hagedorn A.R. , Blackwell R.J. 
Published: December 2007

This paper was prepared for the 47th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in San, Antonio, Tex., Oct. 8–11, 1972 Permission to copy is restricted to an abstract of not more than 30 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Hydrocarbon saturation and its distribution within a reservoir are important parameters in reservoir engineering calculations. One method often used to obtain these data is direct measurement on cores taken from the interval of interest. However, such measurements on conventional cores may result in incorrect values for one or both of two reasons:

some hydrocarbon may be flushed from the core by mud filtrate invasion during coring, and fluids may be driven from the core by gas expansion as pressure is reduced during surfacing.

Pressure coring is designed to en the latter by maintaining pressure on the core as it is retrieved.

This paper summarizes our experience with pressure coring. Design of the present pressure pressure coring. Design of the present pressure core barrel is reviewed, and current operating procedures and core handling and analysis procedures and core handling and analysis techniques are discussed. Field experience is summarized by describing a variety of specific applications.

Introduction

Knowledge of both hydrocarbon volume and its distribution within a reservoir is important for estimating reserves and for planning commercial development. Ideally, one would like to obtain samples from the formation of interest in their original state and measure saturations directly. Such measurements on conventional cores, however, may result in incorrect values for one or both of two primary reasons:

some hydrocarbon may be flushed from the core by mud filtrate invasion during the coring operation, and additional fluids may be driven from the core by expanding gas as the pressure is reduced during surfacing.

Under some conditions, flushing by mud filtrate can be minor; if this is the case, valid fluid saturations can often be obtained using a pressure-retaining core barrel to prevent loss pressure-retaining core barrel to prevent loss of fluids by gas expansion.

Laboratory observations suggest that significant reduction in oil saturation by gas expansion is more likely to occur in water-wet cores than in mixed-wettability or oil-wet cores. At low oil saturation, the capillary forces in mixed-wettability or oil-wet cores will inhibit expulsion of oil by gas whereas this would not be the case for water-wet cores. This behavior suggests that the use of a pressure-retaining core barrel should be particularly beneficial for coring water-wet formations.

The use of a pressure-retaining core barrel is certainly not new. The first design for and application of such a core barrel was reported by Sewell of Carter oil Company in 1939.