--> Abstract: Using Geochemistry and Basin Modelling to Study Oil to Gas Conversion in Block 2/4, Norwegian Central Graben, by N. Mills, H. J. Schenk, and B. Horsfield; #90987 (1993).

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MILLS, NIGEL, Saga Petroleum A/S, Hovik, Norway; and H. J. SCHENK and B. HORSFIELD, KFA, Julich, Germany

ABSTRACT: Using Geochemistry and Basin Modelling to Study Oil to Gas Conversion in Block 2/4, Norwegian Central Graben

Block 2/4 is located on the Norwegian Continental Shelf, in the North Sea Central Graben, close to the boundaries with UK and Danish waters. The crude oils occurring in Upper Cretaceous/Tertiary and Jurassic reservoirs exhibit a wide range of gravities and are all thought to have been sourced by the Kimmeridge Clay Equivalent. Prior to drilling, it had been forecast that the reservoir temperature in the Saga 2/4-14 well would exceed 160 degrees C and that the prospect would contain only gas. Instead, a 49 degrees API gravity fluid was encountered. Because the reservoir appears to have been totally enclosed in shale, it can be assumed that the high gravity oil had formed by the in-reservoir cracking of a medium gravity oil, rather than by displacement phenomena. It was therefore consid red to be well-suited for calibrating laboratory heating experiments aimed at determining the kinetic constants for oil to gas cracking. Programmed temperature closed system pyrolysis (MSSV method) was performed at heating rates of 0.1, 0.7 and 5.0 degrees C/min, in some cases up to temperatures as high as 650 degrees C. The chemical compositions of both oil and gas components with increasing thermal stress were measured on-line using gas chromatography,. With increasing temperature, significant gas (C<1>-C<4>) generation was accompanied by a progressive decrease in the yield of paraffins and by aromatization reactions. Kinetic modelling of the oil to gas conversion resulted in a narrow gas potential vs activation energy distribution between 66 and 70 kcal/mol and a pre-expon ntial factor of 1.1 x 10{16} sec{-1}. For the purpose of numerical simulation, the 2/4-14 well was divided into 38 events extending from the Permian to the present day, each with its own defined lithology and burial history. A heat-flow history was determined by calibration of maturity parameters in nearby wells. Applying the kinetic model to the study area, a very low oil to gas conversion was predicted, a result that is in accordance with the composition of the recovered petroleum.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.