Time Lapse Neutron Logging Improves Formation Evaluation and Reduces Rig Time in the Gulf of Thailand

摘要

In Chevron's Gulf of Thailand ('GOT') operations, costs drive logging and formation evaluation. Programs for logging and evaluation are based on consideration of perceived value and the potential for comprehensive utilization. Well lifespan is short, and economics rarely provide for the use of higher technology at non-discounted prices. A recent business initiative recognized that oil vs gas fluid identification from logging measurements was a risk that should be mitigated providing a major opportunity to add value. Historical experience has shown, that the diameter of invasion can be greater than twenty inches by the time a well is logged with wireline which is beyond the limits of investigation for density and neutron tools, rendering the interpretation of fluid types ambiguous in most hydrocarbon bearing sands in this basin. To reduce this uncertainty, comprehensive wireline formation pressure programs have been run to assess hydrocarbon gradients but because sands are thin and permeabilities are low these programs have had various degrees of success. LWD (logging while drilling) neutron tools can obtain data prior to invasion. Overlaying the LWD neutron and wireline neutron reveals time-lapse differences between the logs, shows gas intervals, and confirms liquid-filled zones. The technique can also infer inflow permeability for some of the more shaley gas reservoirs. Positive fluid identifications have been confirmed by follow up wireline pressure gradients, NMR logs, and production tests. This paper will show many great examples of the evolution of a good idea. It will also demonstrate the effective use of technology, the buy-in from drilling engineers, and value of information benefits to the asset teams. Logging programs in the GOT once thought to be static, have rapidly evolved with insightful technology and the demonstration of its value.