Post mortem at Mukluk

Right after he became Sohio’s district geologist for Alaska in the early 1980s, Mohamed Abdel-Rahman was selected by the company, BP’s predecessor in Alaska, to head up the post-drilling technical evaluation of what went wrong at of the $1 billion Mukluk exploration well, touted as the most expensive “dry hole” in history.

Except it wasn’t a dry hole. In addition to the extensive oil staining, operator Sohio found “residual asphaltene — rich heavy oil, as in tar rich” — said Abdel-Rahman, currently Royale Energy’s vice president for exploration and production, and the reason the California oil and gas company took more than 100,000 acres in the state of Alaska’s Dec. 7 North Slope lease sale.

“What was left was the heavier oil that had a high component of asphalenes. We believe the asphaltene-rich oils were a component of the Mukluk oil pool but were segregated by gravity and/or by an element of biodegradation.

And even though the results at Mukluk shocked the oil and gas industry, which expected Sohio to find a huge amount of oil, the geologists who did the risk assessment on the well before it was drilled gave it a 50 percent chance of success.

“There was one chance out of two that it would be a success,” Abdel-Rahman said.

No one should have been surprised, he said, just disappointed.

“Oil had leaked out through an erosional surface known as the Lower Cretaceous Unconformity, or LCU. … The irony is whenever we analyze a prospect we have to list the elements of risk … the major risk factors in the prospect. And one of the major risk factors in Mukluk was not knowing what kind of rock was deposited over the Lower Cretaceous Unconformity — was it shale or was it sand. That to us, to Sohio, was a big unknown when we drilled Mukluk. Now some of the wells drilled in the North Slope did not have any sand immediately overlying the LCU, they had shale. And that was what we were hoping to get at Mukluk. Instead we got sand — thin transgressive sand called the ‘Foran sands,’ which acted like a carrier bed, but in this case it was a ‘thieve zone’ that leaked the oil from a full Mukluk into the stratigraphically higher zones of the Kuparuk field. Before filling Mukluk up to spill (as evidenced from the fully stained column of Ivishak sands) the oil was originally stored in a ‘Proto Prudhoe Structure,’ a much larger structure that existed to the north of both Prudhoe and Mukluk,” Abdel-Rahman said.

“The significance of our different views is demonstrated in this question,” he said: “Why did the Prudhoe Bay field have a huge gas cap, and why didn’t Kuparuk and Mukluk have any? When one thinks of hydrocarbon charge you have to think of the entire petroleum geology story.”

The “bottom line is … we believe we know what we are doing; we believe we got prime acreage in a prime position,” Abdel-Rahman said of Royale’s North Slope lease selection.

—Kay Cashman