Choosing Between Optical Fiber and Multiple Single-Point Sensors for Real Time Matrix Acidizing Optimization with Coiled Tubing-Conveyed Telemetry
Authors: Livescu Silviu , Craig Steven , Roux Pierre-Francois , Baker Mark 
Published: November 2020

Abstract
Telemetry systems with coiled tubing (CT) have been extensively used in the last decade for many types of operations, such as stimulation and logging. Many studies, reporting improved safety, and efficiency and reduced cost, have been published about using CT-conveyed telemetry systems with electrical wires, optical fibers, and, in the last year, hybrid wire-optical fiber tubes. In this paper, a new telemetry system consisting of multiple single-point sensors in the bottom hole assembly (BHA) and CT-conveyed electrical wire is reported to help optimize matrix acidizing stimulation in real time.
While distributed temperature sensing (DTS) and distributed acoustic sensing (DAS) with CT-enabled optical fiber telemetry systems have been traditionally used for improving the treatment placement during matrix acidizing operations, they have several limitations. Firstly, the optical fiber is placed inside CT. Thus, the distributed data is acquired over several-hour-long periods with the CT stationary in the well, after pumping has stopped. Secondly, the mathematical models published in literature to convert the distributed data into flow rates along the CT length are very complex. All distributed data is qualitatively visualized in the CT cabin and interpreted by the personnel on location. Quantitative data interpretation is usually performed after the operation was completed. These two limitations can be overcome by using multiple single-point temperature sensors in the BHA, that are in direct contact with the wellbore fluids.
The results from two matrix acidizing operations performed in the Middle East in 2020 with two different CT-conveyed telemetry systems are discussed and compared. The first telemetry system used an optical fiber inside the CT. DTS data was used to qualitatively visualize the temperature profile during several hours after bullheading the treatment. The second telemetry system used an electrical wire and three single-point temperature sensors located in the BHA to qualitatively visualize the temperature profile along the BHA while pumping the treatment through the CT and jetting it radially through the BHA. The advantage of the optical fiber system was that distributed temperature data was acquired along the entire CT length. The advantage of the multiple single-point sensors system was that the temperature data was acquired in real time, promptly helping the personnel on location decide to adjust the treatment pumping schedule on the fly.
This is the first study available in literature consisting of field data acquired by using two different CT-conveyed telemetry systems during two matrix acidizing operations. Temperature data and learnings from the two telemetry systems are explicitly compared, helping the industry understand how the matrix acidizing operations can be improved by placing the optimum volume of acid at the required depth for best post-stimulation well productivity and lowest stimulation cost.