Real-Time Monitoring of Acid Stimulation Using a Fiber-Optic DTS System

摘要

This paper discusses a unique system that combines a fiberoptic distributed temperature system (DTS) to measure the distributed temperature across the entire wellbore and a molecular telemetry transmission system that provides a single-point determination of bottomhole pressure. The system has been used to perform real-time downhole monitoring of multi-stage acid-stimulation treatments performed on wells that contain multiple non-isolated pay intervals. The fiber-optic for the DTS is contained inside a length of capillary tubing, which is placed concentrically inside a larger size capillary tubing. The created annulus between these two strings of capillary comprises the molecular transmission system for determining the bottomhole pressure. Real-time-distributed temperature data and single-point bottomhole pressure data are provided on location. In the case history presented, the temperature profile across the multiple pay intervals yielded valuable information for identifying which zones were “taking” the acid, allocating how much acid these zones were taking (relative to one another), and identifying the zones not taking acid. This allowed on-the-fly changes to be made on-site in real-time regarding the make-up of the acid treatment, the pumping rates, and when and where to apply diversion processes. This system enabled the operator to continuously monitor the wellbore temperature across the interval that was being stimulated as well as from a single-point bottomhole pressure below the lowest perforation. In this case, the system was deployed inside the work string used for the acid stimulation, but the system can also be permanently deployed. The nominal ratings for this monitoring system are 250°C and 10,000-psi. This allows the system to be applied in a large number of wells, either onshore or offshore. Furthermore, there are no downhole electronics and no moving parts, making the system extremely well suited for harsh environments.