One of the main challenges in a water drive gas reservoir is to track fluid movement as water breakthroughs occur frequently with depletion. The understanding becomes more challenging when the structure contains seismic/sub-seismic faults with the associated drive mechanism being edge water. Moreover, surveillance options are also limited for such reservoirs if they are producing through short string of a dual completion.
Dual string completion is a cost-efficient technique as multiple reservoirs can be completed in a single wellbore. However, surveillance / logging cannot be performed across perforation intervals of upper reservoir due to operational concerns. As a result, the short string production can only be surveyed through the long string with the help of tools which have deep scanning radius extending beyond tubing and casing into the formation. One example of these advanced tools is Spectral Noise Logging (SNL) combined with High Precision Temperature (HPT) logging which have been used worldwide for such applications.
This paper presents SNL-HPT results of two dual string wells completed in Eocene age carbonate reservoir. A total of nine wells are producing from the reservoir and the Gas water contact (GWC) was not encountered in any of the wells. Selected wells are located on either side of the structure with Well A producing 1.0 MMscfd gas and 1300 bbls/d water while Well B is producing 2.0 MMscfd gas and 800 bbls/d water.
The reason of high water production from both wells was initially attributed to the presence of a high permeability streak in lower part of the reservoir and/or possibility of channeling behind casing. However, results of the SNL-HPT in both wells indicate signatures of fault or fracture flow. The major water production is coming from the middle and lower part of reservoir.
Based on these results, the trajectory of one development well was optimized. The perforation interval of another well was also decided in accordance with the SNL-HPT findings, which resulted in water-free gas production.
Quantification of reservoir flow profile in short string of dual completion well is possible through noise and temperature logging. This information would help in deciding appropriate workover strategy in existing wells and completion design of new development wells.
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