The current economic structure of the petroleum industry often requires multiple completions with production from each zone commingled to reduce completion costs. However, these multiple completions require a different approach for analyzing the effectiveness of both the original completion and possible later stimulation treatments: rather than costly individual zone testing, production logs can be run to detect the contribution of each zone to the total production rate.
When multiple pay zones are treated and evaluated together, the reservoir engineer faces the problem of determining whether or not each zone benefited from the chosen treatment. In the case of multiple completions, well testing using either drawdown and/or buildup is expensive and complicated. Production logs make it possible to determine the type and rate of the produced fluids from each individual zone in a timely manner. By comparing the logging tool responses taken before and after stimulation, the effectiveness of stimulation can be determined. This will identify zones requiring further treatment and help determine the optimal type of treatment. In addition, valuable information for future wells can be gathered efficiently in terms of both time and money.
Guidelines for running production logs are presented and the usefulness of production logs for evaluating multizone completions is demonstrated. Several examples highlight how production logs can be used to analyze multizone completions in tight gas areas.