Dual-string completions are cost-effective to independently develop multi-layer reservoirs completed using a single wellbore. However, the upper reservoir that produces through the short tubing string is generally not surveyed across the perforation interval due to safety concerns of tool getting entangled around the long string on exiting below the short-string tubing shoe. Therefore, the upper reservoir producing through the short string can only be surveyed through the long string, which requires logging tools with radii of investigation extending beyond the tubing and not impacted by multiple strings of tubing/casing.
In dual string completions, it is not possible to evaluate the short string production profile with conventional tools. The High Precision Temperature (HPT) and Spectral Noise Logging (SNL) tools have large radii of investigation and can detect reservoir noise and temperature variations caused by fluid flow from the reservoir into the wellbore, through one or several pipe barriers. SNL is effective in identifying the inflow and injection zones of the reservoir and cross-flows/channeling behind casing. The active production/injection zones and the thickness identified using SNL are used as input for temperature modelling to produce quantitative reservoir production or injection profiles. Additionally, temperature modelling requires input of production and injection history, thermophysical properties of the reservoir and surrounding rocks, geothermal profile, hydrodynamic reservoir parameters as well as well trajectory and completion components. Also, in geographical locations where significant variation in injection water temperature is observed during day and night, surface temperature variations are to be accounted for in the modeling software.
In this paper three case studies from a middle eastern field are presented where the HPT-SNL technology was used effectively to evaluate short string flow profile in a dual string completion, water/gas breakthrough and cross-flow behind casing.