Real-time geosteering in the Curlew field (Image courtesy of Sam Large of Shell; figures courtesy of Schlumberger)

An oil company employee can only attend so many trade shows, listen to so many papers, and read so many technical journals. He or she also has a full-time job finding efficient ways to produce reservoirs. And often the best available technology for a particular problem is not well-positioned on that person’s radar screen.

No single company has a corner on addressing the increasing complexity of well engineering today. The nature of the challenge requires close partnerships between operating companies and service companies to develop optimal technical solutions. Shell and Schlumberger provide a good example of the integration of in-house capabilities where the resulting partnership is greater than the sum of its parts. In two recent successes, a strong team of Schlumberger drilling and well placement experts worked closely with the Shell team to extract more reserves from mature fields.

Curlew

In the Curlew field in the UK North Sea, a geosteering solution was needed that could provide high-resolution formation images while drilling to determine the production mechanism of the reservoir. The fact that the reservoir was chalk provided new challenges to the team.

“Compared to the type of reservoirs we normally drill in the UK North Sea, we were out of our comfort zone,” said Alan McQueen, a petrophysicist for Shell. “We spoke internally to Shell technical experts in Norway and Denmark, using their experience to design the best well.”

Time was at a premium, but so was accurate information because locating the fractures was key to developing the reservoir. “The design of the well relied heavily on seismic data that were used to predict the distribution of porosity in the reservoir,” McQueen said. “We planned a long wellpath through seismic anomalies, and it was obvious to the team that we would need to geosteer the well.”

Shell encountered difficulties drilling the primary well and had to sidetrack. However, it made a good offset well, and it was logged with wireline tools, including a formation imaging tool.

“It changed our understanding of the reservoir,” he said. “The wireline tool showed the reservoir was divided into discrete zones of reworked lithology and zones dominated by fractures.”

Armed with this new information, the team ensured it was incorporated into the design of the next well, the hope being that a sidetrack 50 ft (15 m) away from the first well would have similar characteristics. Donald Mackay, LWD business development manager for Schlumberger, recommended well placement using geoVISION, which images the formation while drilling.

“As soon as we saw the log, we knew we had an exact twin,” McQueen said. “Because of the quality of the imaging data, it helped us meet our objective of placing the well in the sweet spot.”

Shell relied on the Schlumberger team to interpret the data coming from the well site and send it to Shell’s offices in Aberdeen. McQueen was in constant contact with the team but never had to contact the rig. “It’s pretty much real time, and the interpretation gets faster the more you drill,” he said.

“This successful example of well placement comes down to detailed planning and having a fully integrated team,” McQueen said. “We delivered the well path because everyone did their homework.”

Draugen

Draugen is a mature oil field in the Norwegian sector of the North Sea. Earlier wells in this field have been highly successful, including one coming onstream at a then world record 76,000 boe/d. Previous wells were located high above the water, with an average horizontal reservoir completion length of approximately 985 ft (300 m).

Two new wells had been planned, targeting remaining oil on the flanks of the field. As these areas had only a thin oil column, placing the wells at the correct depth became the primary concern. “The dual objectives were to stay high above the water whilst not leaving any attic oil,” said Dougal Grant, production geologist with Shell. Based on consultations with other Shell colleagues and Schlumberger engineers, it was determined that the PeriScope bed boundary mapper service would be right for the job.

The service proved its mettle on the first well. “When we came out of the casing shoe, we found the structure dipping a little according to the PeriScope data, which we didn’t expect,” said Gary Colgan, a petrophysicist with Shell. “We adjusted our trajectory accordingly and remained in our target zone.”

Correlation with other logs was good, he said, giving the team confidence that the PeriScope measurements were accurate. On occasion, the drillstring was only 20 in. below top structure, and the team was able to maintain that distance throughout a lengthy section of the downwardly dipping trajectory. “Eventually we came out of this dipping structure and were able to drill horizontally, but certainly if we didn’t have the PeriScope in the toolstring, we would have drilled straight out of the shoe into the shale and then have had to sidetrack deeper,” Colgan said. PeriScope allowed Shell to deliver 3,300 ft (1,000 m) of reservoir exposure, more than three times the length of previous producers.

The second well, in contrast, had no surprises, and PeriScope was able to confirm what the team was expecting to see.

Grant added that another ancillary benefit was the reservoir characterization information provided during the drilling process. “I think one of the main benefits we had in selling the tool to management was the improved ability to deliver the well objectives, but in running the tool we also gained considerable additional understanding of the reservoir as we were drilling,” he said. “We were able to continuously correlate horizontally in real time the lateral continuity of formations and beds, enabling us to better understand the type of depositional environment and character of the reservoir drilled.”

The team was also able to add another control point to their dataset. “At the end of the reservoir section we made the decision to deliberately tag top reservoir. We built inclination to 95° and via PeriScope saw the top of the reservoir coming closer and closer,” Grant said. “We topped out through it on purpose, confirmed by circulating bottoms-up and finding cuttings showing shale. That adds another valuable piece of information to help reduce the gross rock volume uncertainty.”

Having an integrated team helped manage the vast amounts of data coming in from the well site. “It requires quite a lot of thought and interaction between geophysics, geology, and petrophysics — you really need all the disciplines around the table,” Grant said. “There are an awful lot of curves that come in, and having the Schlumberger well placement engineers there providing a full service rather than just the logs was really necessary.”

Schlumberger and Shell both see the benefits of these successful collaborations, and the organizations strive to replicate this around the world.