Offshore Acid Stimulation, Reaching New Limits

Abstract With long horizontal sections on carbonate reservoirs being more common on the Middle East, the industry needs to contagiously evolve to match the market needs. Not more than 10 years ago reservoirs were stimulated with acid dosage of 100 to 150 gallons per foot (gpf); nowadays is common to find 10,000 ft. horizontal sections requiring around 24,000 bbl. of acid to meet the 100 gpf request bringing new levels of complexity to offshore operations. Since the inclusion of the high volume/high pumping rate vessel to our customer's offshore oil fields the average volume is around 5,000 bbl. of acid systems and, thanks to the 200,000 gal. below-deck raw acid storage capability, it was possible to perform an acid stimulation connected to an offshore platform by a high-pressure flexible hose to pump 10,500 bbl. of 15% hydrochloric acid (HCl) system at an average pumping rate of 20 bbl./min. and wellhead injection pressure (WHIP) of ∼2,200 psi. This operation set a milestone for offshore (barges and rigs) operation in the region. Due to its versatility this stimulation vessel has the capability to also pump at low pumping rates (down to 0.3 bbl./min.) for coiled tubing operations and it has been assigned to execute stimulations in offshore environment and island wells which is a hybrid set-up where, having the vessel docked at the island's jetty, it is required to rig-up up to 5,200 ft. of 3in. treating lines being able to pump acid treatments at 35 bbl./min. in an inland well. All these while transmitting in real-time the operation parameters with our customer in town. The bigger the better, stability issues have been reduced due to the vessel's length and weight allowing it to stay offshore longer time in a safer and comfortable way for the crew on board. Also, it was possible to reduce the number of vessels trips for re-loading purposes on operations above 3,000 bbl. for 15% HCL systems and 2,000 bbl. for 28% HCL systems, leading to reduce the diesel consumption and CO2 emissions of the rig and barges and the vessel itself (marine and stimulation engines). This time optimization is also considerably reducing the cost of the operation by doing a 10,500 bbl. job in 2 days’ rig-time instead of 6 to 7 days as it was being done before.