Kuwait Oil Company is producing more than 1,000 barrels of oil per day from wells that had not produced anything for more than 15 years.
Kuwait Oil Company (KOC) drilled the first horizontal wells targeting the Mauddud Reservoir more than 15 years ago. However, they did not produce for very long. Despite numerous attempts and experiments to restart production of the openhole completions, success proved elusive. Inherent characteristics of the formation, such as a high gas-oil ratio (GOR), make oil production a challenge.
In a recent attempt at fracturing with acid that tapped into a high-pressure gas zone, the gas blocked production of the oil that KOC was targeting. After several attempts to solve the puzzle, KOC consulted Halliburton.
Halliburton recommended using SurgiFrac NWB (near wellbore) service with the Hydra-Jet SPT tool to create carefully controlled fractures that stayed well within the oil.
As of late 2014, Halliburton used this combination to fracture five wells. Sustained production from each well averaged approximately 1,000 BOPD. In each case, new production from the wells paid for the cost of SurgiFrac NWB service in less than a week.
The Mauddud formation in Kuwait has low pressure and tight permeability. All attempts to restart production of the KOC wells through multistage fracturing and high-volume acidizing were short-lived. Wells might flow for a few weeks after the expensive treatments, but would quickly die again. Fractures propagated into an area containing high-pressure gas. Gas then broke through, choking off the flow of more valuable Mauddud oil.
The challenging reservoir created even more complex completion challenges. The wells proved so difficult and expensive to produce that KOC decided to focus its workover activities on wells with higher economic potential. Despite large volumes of oil still in place, producing it turned out to be difficult and costly.
Halliburton felt that the non-producing wells with openhole completions might make excellent candidates for its SurgiFrac NWB fracturing service. SurgiFrac NWB service uses concentrated, high-pressure fluid jets to create short, highly conductive hydraulic fractures.
In this case, Halliburton felt that controlled microfracs could extend through the near-wellbore damage, through undamaged rock, and then connect to a well-developed complex of natural fractures. With careful modelling, Halliburton felt the induced fractures would stay within the Mauddud and not break through to nearby gas zones.
Halliburton and KOC then engaged in discussions about deployment of the service. KOC decided not to invest in the cost of a rig to pull tubing. That meant Halliburton had to deploy its tools through 3.5 in. tubing that also had a 2.75 in. restriction. However, the hole itself – which was open – had an ID of 8.5 in.
Two of these three dimensions created huge challenges. First, none of Halliburton’s Hydra-Jet tools would fit through the 2.75 in. restriction. Second, the distance between the jets and the wellbore would decrease the energy that the tool could focus on rock, thus jeopardising the mission.
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To solve the first challenge, Halliburton went back to the drawing board and completely redesigned a new generation of Hydra-Jet tools that could fit through the small restriction in the tubing.
To solve the second problem, Halliburton also created a special variant of the tool called the SPT (self-positioning tool). The SPT’s pressure stream bends the nozzle, decreasing the distance between the jets and wellbore.
With the Hydra-Jet SPT nozzle touching the wellbore, models showed it could generate enough pressure to create 10 to 20 ft microfractures into the formation – exactly what KOC needed to connect the natural fractures yet avoid breaking through to the high-pressure gas zone. Halliburton used nickel when redesigning the tool because of H2S in the gas that had previously been encountered.
All of these changes meant the procedure could be performed in a safer manner by using a coiled-tubing unit instead of a rig, which also helped reduce costs significantly.
Also, the Hydra-Jet SPT tool does not require the use of plugs or packers for diversion. It uses “dynamic diversion.” Dynamic diversion focuses fluid energy on a single point with enough energy to deeply penetrate rock and enlarge the tunnels it creates.
Dynamic diversion also helps ensure that each target interval is treated discretely, receiving only the intended treatment volume and rate. The jetting velocity forces all fluid into the rock despite the 90º turn.
Eliminating the need to set plugs or packers cut a two-to-three week job down to less than a day. Finally, because of the large width of the fractures created, no proppant was necessary to hold them open. This saved additional costs.
After addressing all the technical challenges, KOC and Halliburton decided to try the technique on one well. The test was a resounding success.
Wellhead pressure went from zero to 500 psi. KOC targeted a production rate of 500 BOPD, but initial production tripled that; it soared to 1,500 BOPD. Sustained production doubled their target; it levelled out at around 1,000 BOPD – for three years, not just two or three weeks.
KOC then decided to try the technique on a second well. It too yielded sustained production of around 1,000 BOPD, this time for six months. Since then, three additional wells have been treated. They too are averaging 1,000 BOPD of sustained production – and are still producing. In each well, renewed production paid for the cost of the operation in less than a week.
