Monitoring Horizontal Producers and Injectors During Cleanup and Production Using Fiber-Optic-Distributed Temperature Measurements

Abstract

Abstract This paper describes the application of fiber-optic-distributed temperature systems installed in several long horizontal open-hole completion intervals of production and injection wells in Oman. We demonstrate how distributed temperature data, from both types of wells, was used to optimize completion procedures and improve knowledge of the reservoir and its performance. The Shuaiba reservoir produces 44° API oil from a low permeability micritic lime mudstone, typically 3 md. Initially, gas injection in vertical wells was selected to enhance oil recovery, but producing wells commonly experienced gas breakthrough, gas flaring was undesirable, and surface-compression constraints were encountered. For these reasons the operator decided to phase out gas injection and use line-drive water injection from horizontal wells. Wells were drilled horizontally, with up to 5,000-ft open-hole completions, but varied in effectiveness. Fiber-optic distributed temperature measurement systems were installed in a horizontal water injector and several horizontal oil producers during 2002 to monitor the long open-hole reservoir intervals during well startup, production, and injection. Data from the fiber optic water injector showed that the intervals flooded slowly from the heel to the toe over a period of months, giving the operator improved knowledge of reservoir sweep from this type of completion. The first oil producer exhibited slow cleanup from the heel, enabling a change in pre-production well stimulation procedures to improve cleanup. The results demonstrate that it is possible to monitor long horizontal open hole intervals continuously, during both clean-up and production, without the need for multiple well interventions. This has proved a safe and cost effective solution to improve the operators understanding of the performance of horizontal wells drilled in the Shuaiba reservoir. Substantial savings are expected through DTS surveys, with a one-time installation costs comparable to a coiled tubing run production log. Following the installation, DTS is available to provide survey data for life of the completion. It is not only cost effective, but also data acquisition operation is much less risky. Geological Background Safah field is producing from the Upper Shuaiba Formation of lower cretaceous age at around 6,010 ft subsea. The best reservoir is lightly cemented and the rock is dominantly skeletal wackestone/packstone. Porosities in the Shuaiba Reservoir typically range 20 to 25%, but permeability's are low, rarely exceeding 5 mD. The Safah field has been divided into a vertical series of flow units, baffles and dense limestone layers making up the main and minor reservoir units. The top five flow units are classified as Main reservoir and the rest is Minor reservoir. The baffles are limestone layers with low porosity that have developed in local areas of the field. In parts of the field they are reservoir rock and form no barrier between overlying and underlying flow units. Most of the water injectors are completed across the main reservoir flow unit 3. The monitoring concept is to survey patterns consisting of producer-injector pairs in different areas of the field. Thereafter, the experience could be extrapolated to wells with similar properties in the area.