At the heart of Ziebel’s proprietary technology is the 15mm diameter composite carbon rod which deploys the fiber optic strands or cables securely into the hostile downhole environment. The rod carries 2 multi-mode strands and 4 single mode strands enclosed in a stainless steel tube. The composite is made of longitudinal carbon fibers bound together in a polymer matrix. It is light and extremely strong (10 tons in tension) while being chemically stable and compatible for service in all normally found well fluids.
The rod is manufactured in a tightly controlled continuous process to achieve consistent properties over the typical finished length of 6,200m (~20,000ft). The rod is semi-stiff and has no “memory”, which means it can be coiled on a drum (either 4.2m or 3.5m diameter are used), but when uncoiled it will straighten without trying to hold its previous bend like steel coil tubing.
The rod is stiff enough to be pushed out into the horizontal sections of wells until frictional forces cannot be overcome. The reach limits are determined by the internal diameter of the pipe, the condition and roughness of the internal surface and the amount of debris in the hole. Ziebel routinely simulates the expected horizontal reach of the rod by running the Cerberus software model which predicts when the available push (compressive load) from surface will be unable to overcome the frictional resistance and the rod lock-up in a similar manner to coil tubing.
The carbon rod has been tested for compatibility with 15% HCL acid wash and with scale inhibitor chemical cocktails, which offers the possibility of real-time stimulation monitoring while these treatments are bull-headed from surface, to confirm the effectiveness of any diversion methods employed and that the fluids are being delivered to their target zones correctly.