This paper describes how a patented intervention based DTS logging system can be used to address the many and varied reservoir management challenges faced in declining fields, complex well profiles and complex completion methodologies. A description of the prototype system is provided along with the test results from the test well, and full suite of a Data Management System for Data Acquisition, processing and capabilities for Reservoir Flow Analysis. The paper closes with a draft overview of where this technology may be in the near future.
The use of fibre optic sensing in oil and gas wells has been of interest to many operators since the first installations in the mid 1990's. Fibre optic sensing has mostly been in the form of Distributed Temperature Sensing (DTS), whereby a continuous length of fibre optic cable is incorporated in the completion tubing, generally encased in a small diameter umbilical. DTS used in this way has demonstrated value by providing information on flow allocation, well leakages, well integrity issues, water breakthrough and others. These applications form part of a new well construction and there is limited scope for retrofitting a well for permanent DTS monitoring. There is value to be gained by having an intervention system based on DTS technology.
The project described in this paper takes the proven DTS technology and adapts it for use in a completion monitoring and production logging system. At present time, a lot of effort is made both by the industry players and research institutes to invent fibre optical sensing technology to be added to the system including point and distributed pressure, flow measurements and fluid phase identifiers leading to a complete fibre sensor based production-logging system.
DTS sensors have been included in slickline type configurations but these systems, as with all wireline based systems cannot be deployed into highly deviated and horizontal wells without recourse to the use of a well "tractor". Despite becoming mature technology, these well "tractors" still suffers from difficulties getting into long reach high deviation well sections, not at least in open hole sections. They are also subjected to an increased risk of becoming stuck when going to these limits. Another challenge is that the toolstring length using such transportation device becomes very long, and that it requires extra personnel.
The alternative is to deploy logging tools with coiled tubing, which is a comprehensive rig-up and deployment task. A challenge is also the dimension of the surface system and the handling of this, where rig-up often means 12–24 hours of lost production.
Both the wireline and the coiled tubing operations requires a substantial amount of hardware, lifting operations and personnel, and it involves spooling up and down of wire or coiled tubing. This is a HSE issue as well as a high cost. And using these methods, conventional logging tools must be moved up and down to perform a survey of several zones, with necessary shut-in (lost production) during tool relocation. The new downhole sensing system described in this paper does not need to be relocated during surveying of several zones, which are time saving and a significant improvement in personnel safety.
The dimension of the new ZipLog™ surface deployment system and the logging rod is of such a compact size, that rigup and deployment on wellheads having very limited headroom above are made possible. ZipLog™ allows surveying to be performed in wells where access with wireline has not been possible, replace wireline plugs in horizontal wellheads and to enable limited rig-up interventions.
The method described in this paper utilizes DTS fibre optic cables embedded in a small diameter carbon fibre spoolable rod. The system has the attributes of a small diameter coiled tubing unit with the benefits of fibre optical based sensing along the whole spoolable rod.