Pressure Evaluation Methods - Leman Field

This paper was prepared for the Second Annual European Meeting of the Society of Petroleum Engineers of AIME, to be held in London, England, April 2–3, 1973. Permission to copy is restricted to an abstract of not more than 300 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 OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal 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 discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abstract A study to determine the most suitable pressure evaluation techniques for Leman Gas pressure evaluation techniques for Leman Gas Field is described. The field is of such a size that pressure behaviour in the reservoir is still transient, so only transient evaluation techniques have been considered. Three main considerations influenced the final choice of procedures and the methods of evaluating them. Firstly, the type of field operation allows little time for detailed well testing using bottom hole pressure recorders. Secondly, the data obtained from the evaluation of well tests is required as input for a 2-D areal, numerical model of the whole field. Thirdly, the field geology is complex and affects the pressure behaviour of most wells even during short well tests. As a direct consequence of the latter factor, existing evaluation techniques have been modified to make them more suitable for Leman Field conditions. These three factors and the evaluation of the procedures finally adopted are discussed. The procedures described in this paper fall into two separate categories: firstly, methods for measuring the decline in reservoir pressure; secondly, methods for analysing bottom hole pressures, recorded during multi-rate flow tests and build-up surveys. The former methods are based on measurement of tubing head pressure, supplemented by a means of estimating reservoir pressure from an extrapolation of short pressure build-ups. The latter analyses have been based on methods already accepted in the industry but modified to suit the complex Leman Field reservoir geology. Introduction The Leman Field in the North Sea was discovered in March, 1966 and further appraisal proved it to be a very large gasfield covering an area of approximately 60,000 acres. The field lies mainly under two North Sea leases; one of these, block 49/26 is operated by Shell UK Exploration and Production Limited, owned 50 percent by Shell and 50 percent by Esso; the other, block 49/27, is operated by Amoco. Reserves of the whole field are currently estimated to be about 10.5 trillion soft.