Lack of real-time downhole data for accurate depth correlation and precise control of pressure actuated tools, often result in inefficient coiled tubing (CT) interventions. Surface readouts have been conventionally used to infer downhole conditions during CT operations; however, the presence of the above-mentioned unknowns along with dynamic wellbore conditions make surface measurements an insufficient approach for knowledge of the actual downhole conditions. This study describes how access to real-time downhole measurements was gained by using CT fiber-optic downhole telemetry and how its implementation contributed to address operational challenges encountered during CT abrasive perforating interventions in Pakistan.
The application of CT equipped with fiber optics and instrumented bottom hole assembly (BHA) to vertical wells in onshore Pakistan required specific designs and new processes for preparing, executing, and evaluating well interventions. Planning and design considerations included selecting the BHA and performing pre-job quality checks of the optic fiber. This novel approach leveraging fiber optic telemetry relies on fibers inside an inconel tube within a CT string, and a downhole BHA that includes pressure and temperature gauges and a casing collar locator (CCL). The BHA acquires real-time data providing quantitative feedback of downhole wellbore conditions during the interventions, which enables accurate placement and controlled actuation of the hydraulic abrasive perforating gun.
Depth accuracy for tool positioning, and differential pressure across the gun nozzles were of utmost importance for suitable abrasive perforating interventions. Downhole pressure gauges monitored the annulus between CT and production liner, and CT internal pressures at all times, helping to keep the differential pressure within the 2200 – 2600 psi for optimum abrasive perforating. The CCL data was utilized to correlate depth for precise perforations placement. Multiple wells were perforated using the combination of CT fiber-optic telemetry and abrasive perforating. The BHA delivered real-time downhole data, which helped to understand the changing wellbore conditions. Implementation of this new methodology increased the operator’s confidence with abrasive perforating, as previously very little downhole data was available to make informed decisions to optimize such interventions and ensure effective perforating at target depth. This study introduces a novel perforating technique in Pakistan. The use of CT fiber-optic downhole telemetry is not limited to perforating, and the BHA can also acquire gamma ray, tension and compression forces, torque, and even flow data. Such systems can have a significant impact in overcoming intervention challenges faced today in Pakistan.