Well Logging In Middle Eastern And Similar Large Reservoirs

The Middle East has large proven oil reserves, and further reservoirs continue to be found. In exploration work, the concessions are large and the targets are large oil fields, which can overcome the high cost of development and transportation. Intensive exploration and development drilling occurred immediately prior to and after World War II, which was about the same time that well logging was becoming an accepted routine technique. The whole background to the development of the Middle East oil fields, the nature of the targets, and the cost involved affected the application of and attitude to logging. Modern logging techniques are, in general, quite adequate for routine exploration and development well applications. After development of a field one of the constant aims is to produce more of the reserves more efficiently and hence more cheaply. Unexpected water production from individual wells proved to be a costly production problem. This was partially solved by routine field-wide checks of the position of the oil/water contact using a through tubing chlorine logging tool. Results obtained with this tool, showed that regular monitoring of the rise in oil/water contact over a producing field, gave invaluable data for more efficient production and reservoir control. The chlorine tool has severe limitations. The development of the thermal neutron die-away technique has produced a tool which has far less restrictions, and hence a much wider application. Results of field trials illustrating this are given. It is considered that the thermal neutron die-away technique could be used through tubing in production wells. The use of the results to obtain quantitative estimates of changes in relative fluid content of the reservoir rock with production, appears to be a real practical possibility. It would appear that there is a direct application for routine logging throughout the production history of an oil field. Basically the necessary technique has been developed and proved. Various problems, both practical and theoretical, still need to be solved. It is concluded that more effort should be given to these logging applications and to the problems associated with them.