Data Acquisition and Processing of Carbon Rod Conveyed DTS and DAS in Very Long Horizontal Wells: First Trial in North Sea Danish Sector

Abstract

Abstract This paper describes the planning, execution, data acquisition and processing of Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS) conveyed by patented semi-stiff Carbon Rod (CR) in very long horizontal wells. The primary interest in CR starts from its dual nature as a conveyance method and an acquisition tool; it is able to access long horizontal sections and record meaningful flow profiling data. CR presents viable alternative to Coiled Tubing (CT) or tractor conveyed wireline logging tools. When a point pressure and temperature tool is required, it can be conveyed at the end of the CR. This paper provides information on the preparation and execution of a three wells campaign in the Halfdan field, the first in the North Sea Danish Sector. The CR-conveyed DTS and DAS technology has been successfully and safely tested for the first time in this field. The CR was run in two injector and one producer wells. The campaign has proven the technology advantages and highlighted some learning opportunities. This paper will also describe the processing and visualization of the Temperature and Acoustic profiles and the challenges involved in handling a large volume of data (Terabyte scale). The semi-stiff CR sensing tool consists of the CR (15 mm in diameter) itself and a bottom-hole assembly (BHA). Embedded in the CR are six optical fibers. Two multi-mode fibers are dedicated to DTS and one single-mode fiber to DAS. The three remaining single-mode fibers are dedicated to Point Pressure, Point Temperature and Vibration measurements. The Fiber Optic (FO) point Pressure (P) and Temperature (T) sensors are located in the BHA. The system provides temperature and acoustic profiles along the rod during the operation. These sensors, in conjunction with surface read out and bottomhole gauge data, provide a comprehensive tool for real-time surveillance and dynamic well analyses. Although hole conditions were challenging, with the first well exhibiting a great deal of scale that impeded a smooth descent, CR was successfully deployed into the three wells. The rod was pushed into the horizontal sections with a reach performance equivalent to that achievable by equivalent small diameter coiled tubing. The maximum reach of CR was more than 15,400 ft MD, with a record of more than 5,100 ft reach into the horizontal section, without using a well tractor or CT to assist deployment. The sensing campaign produced more than 50 TB of well data. The interpretation results will be presented in a subsequent publication. The aim of this paper is to serve as a reference in the planning of CR deployed DTS and DAS applied for well and reservoir surveillance.