The well stimulation and water shut off (WSO) job in the carbonate reservoir of Ghawar field in Saudi Arabia is becoming increasingly challenging, considering the complex well completion. Many challenges are therefore encountered during coiled tubing (CT) interventions when trying either to permanently shutdown water production or to temporarily isolate the water zone to stimulate the oil intervals. In fact, the lack of real-time bottom-hole control of mechanical or chemical diverters caused these jobs to fail with conventional CT strings, which eventually called for costly solutions using workover rigs.

This paper describes multiple shortfalls of previous WSO and matrix stimulation jobs, and how this trend is reversed after the emergence of the fiber optic enabled CT (FOECT) string with real-time downhole measurement sensors.

The permanent zonal isolation utilizing an inflatable packer with cement plug is now possible with greater accuracy and enhanced success ratio even in wells with complex completions. The availability of a real-time casing collar locator (CCL), bottom-hole temperature (BHT) and differential pressure readings enables adequate control of packer setting depth and inflation, and optimization of the cement design and its injection.

The temporarily zonal isolation using chemical diverters can now be assessed real-time with the Distributed Temperature Survey (DTS). The stimulation fluids will not be pumped unless the isolation of the water zone is confirmed. The CT acid job can be now optimized by eliminating the risk of losing acid into the water intervals and by ensuring a uniform acid coverage across the oil zones with DTS.

This method was validated with the wireline log run just before the CT job. Challenges, design, execution and results of zonal isolation interventions with both conventional CT and FOECT are detailed in this paper to demonstrate that this type of CT job becomes more successful with the FOECT.

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