The hunt for oil 2011.08.03

Written by David Green.

drill.big_rigBy DAVID GREEN

By Friday afternoon, drillers had reached a depth of about a thousand feet on land near North Morenci. The goal is to find oil in the Trenton limestone, deep below property owned by Velma Schaffer.

It’s not as simple as just heading downward, however, because engineers have determined that the oil doesn’t lie below Bigard & Huggard Drilling’s large rig that’s protruded into the sky since July 27.

The prospective oil field is actually far below a swampy area a few hundred feet away. A marsh is no place for a big rig, so eventually the firm will employ what’s called directional drilling. The shaft will begin to veer to the southeast under the swamp before resuming its slow plunge downward.

The finished well will resemble an “S” curve, says Joe Herpst of SRG Services, the firm overseeing the operation for well owner Continental Resources, an independent oil and natural gas exploration company based in Oklahoma.

The Trenton Black River rock formation is well known for natural gas production in New York state and that same formation is producing oil in nearby Hillsdale County. Herpst hopes Lenawee County will soon be added to Continental’s list of productive oil wells.

Considerable drilling activity took place in the North Morenci area in the 1960s, but few natural gas wells were established. In the 1980s, another wave of exploration began when “vibroseis” trucks roamed area roads, sending vibrations down into bedrock to study geologic formations.

Two years ago Continental representatives began visiting land owners in Lenawee and northern Fulton counties to acquire leases to explore and drill on property. Continental now has leases on more than 50,000 acres in Michigan.

Last year teams from a firm studying geologic formations arrived on the scene again, but with newer technology in seismic mapping. Vibrator trucks produce a two-dimensional map of the bedrock; a system using cables and microphones produces a three-dimensional image. Continental has completed 3-D testing on more than 40 square miles in Michigan.

“Technology has changed tremendously,” Herpst said. “3-D seismic has really improved the odds.”

drill.roll_casingOil and gas has collected in fractures, where the rock has broken apart and moved. The fractures have typically been very hard to find, but 3-D has bumped up the success rate. It’s also rekindled interest in Lenawee County exploration.

“Companies that have been able to decipher the information have had pretty good success,” Herpst said. 

Drilling technology has changed, also, and prospectors are able to place a well fairly close to where they want it.

A well near North Adams where Herpst recently worked went down about 4,200 feet, then took a 90° turn for another 1,800 feet. The angle on the Schaffer land won’t be that extreme, but directional drilling does slow down the process some. Herpst expects the initial drilling to be completed next week.

Heading down

The first stage of drilling proceeded to the 300-foot depth when the operation was halted and steel casing was installed. One at a time, 40-foot sections were dropped down the shaft and screwed together.

Next, a cement-pumping truck arrived with a high-pressure pump that pushed cement inside the casing. The process forces cement to the bottom and then it flows back up on the outside of the casing. Work comes to a halt while the cement sets to hold the casing firmly in place.

The first stage, with 11-3/4 inch diameter casing, is installed to protect groundwater sources.

Stage two, the intermediate phase, continued to a depth of 1,000 feet. This time 8-5/8 inch casing was cemented into place. When the intermediate stage is complete, Herpst said, there’s a continuous wrap of cement from the surface to 1,000 feet. Michigan law requires the intermediate casing for added protection.

Progress will depend on the performance of the triple-headed drill bits. Bits get torn up, Herpst said, and mechanical breakdowns can occur. Changes in the structure of the rock also affect progress.

When the hole reaches the final depth, electronic equipment will produce logs providing a variety of data about the rock properties.

“This will allow geologists and engineers to evaluate the rock and see whether they want to pursue it further or whether it’s a dry hole,” Herpst said.

If the decision to proceed is made, a smaller casing will be run to the bottom of the hole, more than half a mile deep. Herpst said. 

“If the well is successful after we run the casing, all of the equipment will clear out and they’ll bring in a smaller rig to do what’s called ‘completing the well.’”

drill.concrete_truckPerforating guns will blow holes in the casing at selected levels to allow oil to flow inside. Generally, acid is pumped into the casing to clean out cement and rock debris. 

If this isn’t enough to allow the flow of oil, a mixture of water, sand and chemicals will be pumped into the well in a sometimes controversial, 60-year-old practice known as hydraulic fracturing (fracking).

The rock found in this area often needs nothing more than the acidization process, Herpst said, but fracking can be used to enhance performance.

Concern about fracking is prevalent in many states, and each state creates its own regulations. Michigan tightened its fracking rules in May, although there are critics who don’t think the regulations go far enough. 

Budget cuts at the state level could prevent adequate oversight, critics say, particularly in the rate of water withdrawal.

The Michigan Department of Environmental Quality reports that fracking has been used on 12,000 Michigan wells since the 1960s without any environment harm.

Numerous wells in Hillsdale and Jackson counties are meeting the maximum withdrawal rate of 200 barrels of oil a day, Herpst said, and several are capable of producing much more. The limit was established to prevent flowing wells too hard and bringing water up into the oil.

If the Schaffer well proves commercially productive, Herpst said two to four storage tanks would be brought in. A tanker truck would visit the site occasionally to remove the product.

Oil and gas have been captured in a few locations in Lenawee County, but this well would mark the first for Continental, and the furthest south the company has explored in Michigan.

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