The current economic structure of the petroleum industry often requires multiple completions with production from each zone co-mingled to reduce completion costs. However, these multiple completions require a different approach to analyze the effectiveness of both the original completion and possible later stimulation treatments of low permeability formations. To reduce the financial impact of individual zone testing it is desirable to run production logs to detect the contribution from each zone to the total production rate.
Some wells encounter multiple low permeability pay zones that are uneconomical to complete and stimulate individually. If the well does not do as expected or has a problem producing, the problems may not be recognized by conventional testing. If multiple zones are stimulated simultaneously there may be a concern whether each zone was responding to the stimulation treatment. Radioactive isotopes are used as a tag during the stimulation process to measure completion and/or placement effectiveness. Other methods for evaluating stimulation treatments include well testing, using pressure drawdown, and/or buildup analysis. However conventional analysis’ techniques are complicated to interpret with multiple completion intervals and may not yield information on the flow capacity of each zone.
With production logs it is possible to detect the type and rate of the fluids being produced from each individual zone in a timely manner. By comparing the open hole log analysis to a production log after stimulation it is possible to determine the effectiveness of the stimulation. This information could serve as a knowledge base for future stimulation design and improved well performance. Further computer analysis of the openhole logs, production logging data, and stimulation information could provide additional insight to enhance the economics of the reservoir development and to help understand wells that are producing below their expectations.
This paper will suggest guidelines for running production logs and show the usefulness of using these tools when evaluating multi-zone completions in tight gas sands. A three well example from the Rocky Mountain area is used to highlight the use of production logs to analyze multi-zone completions.