ABSTRACT: Reservoir geochemistry used in solving production problems

Bjoroy, Malvin¹, Peter Barry Hall¹, and Chukwuemeka M. Ekweozor²
(1) Geolab Nor AS, Trondheim, Norway 
(2) Getamme Geochemistry, Nigeria

Reservoir geochemistry was introduced in the mid-80's and has become an important tool in solving production problems. This presentation will address two examples of the use of reservoir geochemistry: A. Determination of separate compartments in Heidrun Field, Haltenbanken, offshore Norway, and B. Evaluation of commingled production in a Nigerian field.

To evaluate the degree of compartmentalisation in the Heidrun/Heidrun North fields, twenty-three oil samples from eight wells were analysed. Geochemical analyses, included techniques ranging from whole oil GC to GC-MS and GC-IRMS were performed. The results of this study, which show that there is a significant degree of compartmentalisation, both laterally and vertically, will be discussed in detail.

To evaluate a method for determining the relative contribution of different reservoirs in a field, analysis was performed on oils from a Nigerian field which consists of two separate sandstone reservoir sequences, both containing biodegraded oil. There are different taxation schemes for the two reservoirs so that the authorities demand separate production. The samples were collected from the different production wells and analysed by high resolution gas chromatography, together with known mixtures of the two types of oils. Since the oils from both reservoirs are biodegraded to a different degree, it was possible to find components in the oil from one reservoir that were not present in the oil from the other reservoir. Ratios could be determined which could then be used to calculate the amount of each oil in a mixture. The results were then used to calculate the percentage of oil from each reservoir sequence in mixed oil samples. The results were well within the accepted range using traditional metering measurements. This study shows that gas chromatography alone can be used to determine the relative contribution of oils from different reservoir sequences in commingled oils.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia