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Abstract
Conventional slick-line temperature surveys enable successive temperature measurements at pre-determined depth stations along the well-bore. This method has two major drawbacks. The wellbore fluid flow dynamics impact the temperature accuracy while the uncertainty in depth leads to erroneous conclusions on spatial temperature distribution along the wellbore. Remedial actions based on these temperature measurements do not always help optimize productivity or injectivity. To overcome these measurement uncertainties and correctly evaluate the gas-lift system performance for the oil producer wells or to identify temperatures anomalies, such as flow behind casing for water injection wells, continuous temperature measurements with time and depth are needed.

The slick-line fiber optics distributed temperature sensors technology presented in this paper measure simultaneous temperature traces along the well-bore with time. This is widely used in oil wells located at Maracaibo Lake, where approximately 95% of the wells are produced using gas-lift and also applied in La Concepcion water injection wells for wellbore integrity. There are technical papers on fiber- optic technology applications as a qualitative monitoring tool but very few case histories where slick-line is used as the method of fiber deployment.

This paper will describe eight success histories where fiber-optic sensors have been deployed using slick-line. These case studies are grouped as follows: Gas-Lift System Evaluation in which four wells were subject to analysis: Completion leakages detection in producers and injectors; Identification of water entry as well as channeling of water behind casing.

This paper will also demonstrate the application of this technology to implement production enhancement techniques. The use of this technology for operational flexibility, time saving and data quality will be compared to conventional temperature logging. In addition, it will show how environmental risks are eliminated by deploying fiber on slick-line for leak detection services.

Introduction
Capturing accurate fluid temperature profiles in a production or injection well is a challenging task, owing to complex interaction of wellbore fluids with its surroundings1. Qualitative analysis of conventional logs in Maracaibo Lake and La Concepcion confirmed that the gathered information was limited for efficient gas-lift system evaluation or wellbore surveillance, because the standard procedures rely solely on temperature measurements at discrete intervals in a limited period of time.

The case studies described in this paper are on the basis of eight field operations using fiber-optic technology as a slickline intervention in brownfield environments. The jobs conducted in four of the wells were primarily for gas-lift system evaluation, where the wells were designed for continuous-flow gas-lift operation. However, the optimal lift performance of these wells was affected by unstable flow conditions typically associated with incorrect valve port diameter size, high water content, lower API gravity oil, more than one valve injecting at a time or variations of gas-lift injection rate due to subcritical flow conditions at the point of operation2.