REAL-TIME MONITORING OF ACID STIMULATION UTILIZING A FIBER-OPTIC DTS SYSTEM

This paper discusses a unique patented process that combines a fiber-optic distributed temperature system (DTS) to measure the distributed temperature across the entire wellbore and a molecular telemetry transmission system that provides a fixed depth determination of bottomhole pressure. The system has been used to perform rea-time downhole monitoring of multi&-stage acid stimulation treatments performed on wells that intercepted multiple 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 2 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. On-the&-fly changes could be made on-site in rea-time regarding the make up of the acid treatment as well as the pumping rate.

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. The system was deployed with the work string used for the acid stimulation but can also be permanently deployed. The nominal ratings for this monitoring system are 250 B0C 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.