The Forties Echo platform originally had a small workover rig on skid beams. The drilling derrick, drill floor and beams were removed from the platform. The Galaxy III rig was jacked up next to the platform in early 2004 to start sidetracking wells. (Images courtesy of Apache Corp.)

Since Apache Corp. took over the Forties Field, the company has identified 302 targets and drilled 161, resulting in increased production and higher remaining reserves. And the drillers aren’t done yet.

Three new satellites were developed in the field area—Bacchus, Maule and Tonto. The Maule and Tonto fields lie above the main Forties Formation and had not been targeted before. Tonto, which came onstream in 2013, was the third new oil field brought online by Apache in the Forties area since 2010, and its success was a direct result of the company’s drilling philosophy.

“One of our strengths is that we will try out new ideas and approaches if they work for us, then fine, we’ll continue. If they don’t work, then we’ll drop them and move on to the next thing,” said Ted Hibbert, senior drilling advisor for Apache. “It’s all about introducing these little pieces of new technology. We try to simplify things as much as possible while encouraging innovative thinking.”

Apache started drilling operations with one crew on the Forties Charlie platform in 2003. Then in early 2004 things really got started when the jackup rig Galaxy I was put over the Forties Echo platform, followed by the Galaxy III. An aggressive redrilling campaign got underway that yielded immediate results.

The biggest challenge for Apache was based primarily on the age of the platforms and equipment. The integrity of the existing wells “was pretty good, BP had maintained them fairly well, which has been in our favor,” Hibbert continued. Before drilling operations could really get underway on the four main field platforms, however, the rigs and equipment needed to be brought up to more modern standards.

Upgrading rigs, equipment
“None of the rigs had been used for more than 12 months. When we started off, we were basically starting all of the equipment from being idle,” Hibbert added.

All of the derricks on the main field platforms were the originals. When BP left, water-based mud and kellys, mud pumps, drawworks and other equipment that had been there for many years was still being used.

One derrick on Forties Charlie, for example, was already more than 40 years old. Apache undertook a renovation program that saw all four derricks recertified, with activity taking place including completely rebolting them, replacing any cracked or corroded braces and recertifying them.

Apache got to work with further upgrades of the rigs. Very quickly it replaced the kellys with rented top drives. Iron roughnecks were fitted on the rig floors to improve safety and increase efficiency. “Over a period of time, we put top drives on all four installations, and the last installation to be converted to a top drive was actually the Forties Delta rig within two years,” he continued.

On three of the four platforms, an additional 10P130 mud pump was added, which necessitated the removal of a cement silo, increasing the number of pumps to three.

An additional mud pump was added on three out of four platforms. Apache converted from the use of water-based mud to OBM for improved hole stability.

Oil-based mud
A decision was made by Apache to convert from the use of water-based mud to oil-based mud (OBM) for improved hole stability. All equipment was converted to allow this, meaning the platforms had to be converted for full OBM containment to keep it from going overboard.

“One of the advantages of using OBM was with all the sloughing shales on Forties. OBM is very good at inhibiting those shales. It basically gave us the potential for drilling a better well―fewer hole problems, reduced pack-offs, fewer washouts and the ability to drill into the reservoir from the 13⅜-in. shoe at 1,000 m (3,280 ft) true vertical depth. We’ve drilled 161 targets and completed 131 wells, not to mention the number of workovers we have carried out,” he said.

The shale shakers on the platforms were upgraded from VSM 100s to NOV/Thule VSM 300s. At the same time ergonomic changes were made by turning the shakers through 180 degrees to allow easier access due to a low roof at the cuttings trough end.

The mud pits were overhauled, and new grating was installed. “We’re in the process of installing Palfinger pipehandling machines. We have two in operation so far on Bravo and Charlie. One of the issues in the winter months is that you actually can be shut down by the weather. If the cranes are down, we can now continue to operate using the Palfinger to transfer pipe or casing to the rig floor. It also allows drilling to operate independently of the platform crane operations.

“Another thing that we did to help us continue to operate through the winter months was to modify some of the original cement silos so we could use them for OBM storage as well. We increased our OBM storage, including base oil, from somewhere in the region of 1,200 bbl to about 1,900 bbl, not a lot for today’s mobiles but significant for us,” he noted.

“We’ve overhauled all the drawworks in the field, as well. You could say, over the period, we’ve probably stripped out just about every piece of equipment that we’ve got on the platform. These are all additional efficiency items to keep us working as long as we can during bad weather,” he said.

People make real difference
Hibbert believes that a lot of the changes that Apache has been able to make have been due to the passion and drive of both the offshore drill crews and the onshore team. BP left a skeleton crew in place that went with Apache. From that crew Apache branched out and utilized its knowledge and experience on Forties.

Through a bid process Noble became the drilling contractor, and it was very much aligned with the way Apache does business. Noble subsequently sold off its platform drilling services to Seawell, which is now Archer (the current contractor), and many of the original Forties people transferred with them. One of the reasons for success is very much the drill crews.

“The guys that work offshore have a can-do attitude, and they’re supported by a like-minded group onshore. If we do have a problem, people are very good at getting together, working out a solution and then going and executing the solution,” Hibbert said.

A lot of the main field upgrades were instigated and managed in-house. The small in-house team also organized the engineering works, which elsewhere would have been left to the drilling contractor with all the associated overheads.

“Basically we organized all of that ourselves, and we got an individual contractor to do the work. That also has saved us a considerable amount of money, rather than giving it to somebody else as a project management activity. For every dollar we spent, we got a dollar’s worth of work in reality,” he said.

Reservoir cuttings injection
Another new technology included in the drilling campaigns involves reinjecting cuttings. In the North Sea operators cannot dump OBM cuttings overboard.

“I’m not aware that there’s anybody else in the North Sea that injects their cuttings into the producing reservoir. I think everybody else is basically injecting cuttings down a separate annulus into a shallower zone. Injecting shallower for us could have created wellbore instability where we would have wanted to sidetrack at a later date. Instead by injecting those cuttings into the producing reservoir, we have avoided instability issues,” Hibbert explained.

The cuttings are ground up and mixed with water in a slurry, which is then pumped into the produced water-reinjection (PWRI) stream at the christmas tree and down the water-injection tubing into the formation. That has worked very effectively for the company. Modifications were made to the BOP deck so the cutting reinjection slurrification skid could be installed and the existing portable cement unit used to inject the slurry into the PWRI stream.

“What you do need to do is make sure you overflush the injection well if PWRI is turned off. You need to make sure that the slurry has gone down the wellbore and quite a way into the formation before stopping injection. We haven’t seen it as a problem so far,” he said.

Pilot-hole drilling
One of the other techniques that Apache introduced is what it calls pilot-hole drilling. “We’ll drill several sidetracks from a single well. We may evaluate two or three targets. We’ll drill to one target, plug it back, drill to another, plug it back and drill to a third one. That may create more targets that we’ll drill later to produce. We’ll complete, say, the final target,” he said.

That’s basically to optimize slot usage, which is one of the limiting factors. The company is building reserves by proving up new targets, but at the same time it ends up with a producing well. “It’s like a mixture of exploration and development all in one wellbore,” he added.

Producing through drillpipe
Hibbert described one solution as one of those “oddball things that we have had to do on one or two wells, which has been the only way we could complete those. We cemented in the drillstring across the reservoir and back into the previous shoe. We then backed off the drillpipe inside the casing, screwed in a liner hanger, crossed over to the drillpipe and perforated the drillpipe. The wells successfully produced for a few years.”

These were wells with quite bad hole-stability problems. Completing the well through the drillpipe was the only solution. Otherwise the well would have to have been abandoned. “It was a bit unconventional, but we managed to get our money back,” he added.

Upside-down whipstock anchor
In collaboration with a service company Apache has perfected what it calls the low-side whipstock. The method helps with reducing problems with milling windows in uncemented casing.

“We’ve perfected running the whipstock upside down so that we are milling the window out of the bottom of the casing. In a normal whipstock the milling might come off left or right of high side. What we’ll do is drop out of the low side of the casing. This allows the casing that is left on the opposite side of the milled window to create a tunnel roof that prevents effectively the hole collapsing in the uncemented area,” Hibbert explained.

By using a Smith Trackmaster whipstock, the whipstock face is locked back against the inside or roof of the casing preventing the whipstock ramp dropping back across the hole and preventing further reentry (see SPE paper 149625 for more detail).

The Smith whipstock with the locked back whipstock face was used for lowside exits.

Openhole gravel packing
Sand production is a major problem in the Forties area. BP previously had opted to manage the sand at the surface. To improve the runlife of the electric submersible pumps (ESPs) in the wells, which are about 45% of the well stock, Apache opted to use sand screens and openhole gravel packs to keep the sand downhole.

“Once upon a time the runlife of the ESPs was one or two years, three years if you were lucky. The longest-running ESPs now have up to seven years runlife. By getting those runlives longer you go back and service a well once every four or five years. That gives you more drilling time during the year rather than having to do workovers, which equals increased production,” Hibbert said.

On the Echo Platform a gravel pack was done off the back of a supply boat to reduce cost. “That was the first time that had been done here. Rather than use a full-spread gravel pack boat, we got the kit on a supply boat. We had to have the certifying authority to verify some things. That worked out quite well,” he continued.

Changing drillpipe
Some of the simpler ideas provide some of the better returns. Take, for example, drillpipe and tool joints.

“We carried out a review of drillpipe that was available on the market. Because we had only two mud pumps early on and the standpipe manifolds had been downrated to 4,000 psi, we were restricted with the flow rate in 12¼-in. hole sections,” he explained.

The company brought in Drilco’s 5½-in. TurboTorque drillpipe. The advantage of this is that the tool joint is the same size as 5-in. drillpipe at 6⅝-in. (no loss of rack back capability), and it has a larger inner diameter (ID). With the larger ID there is a lower pressure drop in the pipe. That allowed the 12¼-in. section to be drilled with higher flow rates since there was less pump pressure lost in the drillpipe and higher annular flow rates.

This tool joint is a connection that makes up faster than other drillpipe connections and also breaks out more easily, being about 50% of makeup torque, which fitted nicely with the company’s iron roughnecks, he added.

Another benefit was that the pipe could be racked in the existing 5-in. drillpipe fingers because the tool joint was the same size. No racking capacity in the derrick was lost. “That was another North Sea first. No one else was using the TT550 pipe here. We’ve continued to use that successfully across all our strings,” he said.

Conductors, wooden guide shoes
Apache has drilled some new surface wells, which has required driving con-ductors. Conductor driving hadn’t been done since the early 1980s.

“To start the conductor driving, we’ve used some simple technology for guiding the conductors through the offset guide rings fitted to the jacket, using a wooden guide shoe. Previously the conductors had been fed through the offset rings using divers and a complex rigging procedure. That’s a demonstration of both low and high technology, which has enabled us to drill several new wells,” he noted.

Essentially it’s a 26-in. wooden cone that goes into the bottom of the drive shoe, made out of laminated timber. Because it’s almost cone-shaped it gets into the offset guides without the risk of going to the wrong side of the guide.

When the conductor comes to a halt in the soft seabed, the company starts hammering it in. That sheers the pins holding the guide cone in place, which allows the cone to ride on the top of the soil plug inside the conductor as you drive the conductor into the shallow formation. When drilling out the soil plug for the next section, all that is being done is drilling out wood—and that’s easy to drill out and cheap, he explained.

Manipulating casing
One of the restrictions with the Forties platforms is the number of available well slots for drilling. Apache has developed some innovative ways of renovating and using those slots.

On one well the 18⅝-in. casing was corroded, and the top end of the well had to be rebuilt. “What we did was get a crossover built from the 26-in. conductor to a starter head. We then cut and pulled 9⅝-in. and a few joints of 13⅜-in. casing just below the wellhead. We cut out the rotten 18⅝-in. casing, which was cemented back to surface. We tied the 13⅜-in. casing back into the 26-in. starter head, which allowed us to sidetrack the well and install new 9⅝-in. casing.

“These innovative solutions allowed us to basically reuse a slot that would have been junked otherwise,” he said.

Casing back-out tools were used on one well drilled from the recently installed Forties Alpha Satellite Platform (FASP). The well unsuccessfully tested a deep target, using a 10,000-psi wellhead. For the next well the wellhead needed to be changed to 3,000 psi to drill a Forties target. By using a casing back-out tool, the 13⅜-in. casing was unscrewed, and a new joint of casing was installed. That allowed the top end of the well to be converted to take the company’s standard equipment.

In an effort to maximize the use of well slots on Forties Echo, two splitter wells were drilled through the two remaining conductor slots. No splitter wells had been drilled on the field before. The 38-in. by 36-in. by 35-in. conductors were set in the two remaining slots.

“We were able to go through the guides in the template, which allowed us to get four wells drilled. One of the wells had an issue, so in the end only three wells were completed. It allowed us to get the equivalent of three additional producing wells onto
the platform,” Hibbert said.

The two wells were literally side by side, an inch or so apart. For each side of the splitter, 13⅜-in. casing was run, followed by 9⅝-in. casing and then 7-in. liners. At the time, these were some of the longest 7-in. liners run, Hibbert added.

Ongoing innovation
The innovations are still going on with the Forties Field expansion.

These include horizontal trees to speed workovers and sidetracks, using seal cans in place of production packers, multibowl wellheads, extended reach wells to the Northwest Bravo Field, casing running tools and drilling into the reservoir formation in a single pass from the 13⅜-in. casing shoe.

All of these innovations have helped extend the productive life of this first generation giant field by another 20 years at a time when there are plenty of other North Sea fields being run down and preparing for decommissioning.

“Basically you have to have a can-do attitude, keep it simple, challenge the norm and think out of the box,” Hibbert noted. “And to make it happen you have to have good people on- and offshore.”

A liner top seal can was used in place of production packers. The tubing and ESP cable run through the seal can. Tubing is run into the seal can, and the hanger is set at the surface. To workover a well, the seal can is pulled straight out of its receptacle. It is a simple, cheap, effective method of sealing the wellbore.

This story is part of a special report. Read each story:

Forties At 40

Reawakening The Slumbering Giant

Editor’s note: Part 2 of the Forties Field special report will appear in January’s E&P issue.

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