INTRODUCTION

As the theme of Panel Discussion No. 3, 'Petroleum Geology', is extremely broad, the theme for discussion was narrowed considerably so as to be concerned primarily with basin evaluation and the three principal factors related to basin evolution.

  1. Basin formation-tectonics.

  2. Basin filling-sedimentation.

  3. Basin maturation-diagenesis of hydrocarbons.

The first two papers are related to basin formation, with data on methods of entrapment, and conceptual ideas concerning the diagenesis of oil and basin maturation. The third paper is concerned with methods for determining the degree of maturation and the detection of prospective zones. The fourth paper treats basin filling: the determining of the types of sedimentation and their environments of deposition relative to prospective zones. The last paper summarizes the factors required to make a good evaluation of a prospective basin.

STATEMENTS, QUESTIONS AND ANSWERS Evolution of the Chinese Continental Margin and Prospective Oil and Gas Resources, presented by Dr. Xie Mingqian, Deputy Leader of the Department of Structural Research, Academia Sinica (China).

Several questions concerning sedimentation in the Chinese offshore areas were directed to Dr. XIE, but unfortunately due to lack of time, the questions were left partially unanswered. With respect to the importance of limestones in the sedimentary sequence, a question raised by R. G. ALEXANDER (USA), Dr. XIE responded that they were indeed important and were oil prone. To a question by D. COOK (UK) as to whether the Paleogene sediments would be more likely to produce paraffinic or naphthenic types of crudes, Dr. XIE said that information was not yet available.

Development of Fore-Arc Continental Margins and their Potential for Hydrocarbons, presented by Dr. Y.

Aoki, Research Geophysicist, Japan Petroleum Exploration Co. (Japan).

Discussion of Dr. AOKI's paper centred around the problem of the existence of gas under the BSR.

R. KLEIBER (FGR) felt that long range migration would be necessary in order to form any gas accumulations, and J. LAHERRERE (France) mentioned that only thin layers of gas (2 cm to 2 m) have actually been encountered. Dr. AOKI indicated that migration distances could be as much as 20-30 km if the methane were produced at the bottom of the trench.

As no wells have been drilled through the BSR, no-one knows the thickness of the possible gas accumulations below. It is true, as mentioned by Mr.

Laherrere, that within the BSR, the gas zones are thin. Mr. YOUNG (Venezuela) mentioned that migration could also be short, with the gas/oil rising vertically through fractures from the accretion zone where temperatures are adequate and the TOC is

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