Making the familiar strange

Lucas and the Michigan Basin Reef Project

American Association of Petroleum Geologists (AAPG)

Author’s note: In 1993, I was asked by Ted Beaumont and Norm Foster to join them in teaching an AAPG course on creative thinking. We needed an example of successful creative thinking in oil and gas exploration to discuss with the class, and I immediately thought of Pete Lucas and his role initiating Shell’s successful efforts in the Niagaran reef play in the Michigan Basin.

I called Pete, and he provided me with new insights on how his ideas evolved in developing the exploration concepts utilized in this very successful play.

The following is based largely on that interview.

This story is an illustration of how a single geologist working for a major company can develop new exploration concepts in a “mature basin” and turn it into one of that company’s most successful plays in the onshore United States.

It took place nearly 50 years ago, but the lessons learned are still relevant today.

The geologist is Pete Lucas, the company is Shell Oil, and the play is the Niagaran reef trend along the northern margin of the Michigan Basin.

Our story starts in 1959, when Pete was assigned the task of determining the exploration potential of the Michigan Basin – a basin that was considered by many to have been thoroughly explored, and any remaining targets being too small to interest a major oil company.

This did not deter Pete; in fact he welcomed the challenge.

He started by examining the basin’s existing producing fields, and became intrigued by potential of Silurian-aged (Niagaran) reefs. At that time, the major reef production from this interval was from the Boyd-Peters reef complex in the southeastern part of the basin.

Pete wondered if any potential remained for similar accumulations in other portions of the basin.

One of his first steps was to construct a series of regional Niagaran cross-sections across the basin. Pre-existing published interpretations, based on isopachs of the Niagaran, outlined a thin area in the middle of the basin identified as the mid-basin high.

Pete had his first “Aha” moment in a hotel room in Lansing, Mich., where he was examining his correlations sections. He literally and figuratively turned the existing interpretation upside down by the simple process of flattening the geologic cross sections at the base of the Niagaran instead of the top. The mid-basin high became a mid-basin low with the thin representing “starved basin” sedimentation, the thick areas became carbonate shelves and the area of rapid change in the isopachs became a shelf margin.

The next step was to test the new conceptual model. Pete was able to show from an examination of core and drill cuttings that the basin thin was indeed a basinal facies characterized by fine-grained, dark-colored carbonate, whereas the thick Niagaran areas contained a light-colored carbonate often characterized by the presence of shallow-water fossil assemblages.

Pete then constructed a series of regional maps in the Michigan Basin. His eyes were drawn to what became known as the Northern Shelf, which was a lightly explored area that had a well-defined transition from shelf to shelf margin to basin.

The standard exploration concept at that time was to explore for reef development and/or porosity along the shelf margin – but Pete also had another idea.

He had read a paper by Phil Playford, an Australian geologist, that identified an isolated “pinnacle” reef outcropping in front or basinward of a well-defined shelf margin of outcropping Devonian-aged carbonates in the Canning Basin in northwestern Australia.

Pete took this idea and postulated that, although none had been penetrated by the limited well control, a possibility existed that hydrocarbon-bearing pinnacle reefs could be present basinward of the Niagaran shelf margin along the Northern Shelf area.

To narrow the exploration area for pinnacle reefs, Pete used a series of isopachs of the Niagaran carbonates and the immediately overlying section of the Salina Evaporites to define a shelf slope in front of the shelf margin that was transitional into the basinal facies. He postulated that this shelf slope area was the most likely area to have pinnacle-reef development.

Of the 38 wells available in the area only about 17 actually provided the key isopach and onlap data to define this 15-mile wide and 140-mile long exploration fairway. The entire unexplored area of both shelf margin and shelf slope occupied an area of approximately 2.2 million acres.

One of the problems Pete had in presenting his ideas to Shell was the pre-existing concept of the time equivalence of facies, often used to map the time-line of basin development by noting the change from shore face to shelf to deeper water carbonates and thick basinward shales to be deposited at least in part at the same time.

Objections were raised that reef development in front of a carbonate shelf was unlikely if the time-equivalent facies were evaporites deposited in very-high salinity water.

Here again, Pete had to rely on a fairly new concept that in a “starved” basin, the thicker infill section, whether shale or evaporate, post-dated the carbonate development.

In other words, in the Michigan Basin, the shelf carbonates and the potential pinnacle reefs in front of the shelf grew first, followed by evaporate infill, which buried the reefs.

Pete was successful in convincing his management of the potential of the Northern Shelf play, and in 1964 several seismic lines were shot along the northern shelf margin.

Unfortunately, the resulting seismic quality was very poor due to the presence of thick glacial drift at the surface in this area. The project was shelved, and Pete Lucas, who was still considered a rising star in the company, was transferred to a new project and new area in the New Orleans office.

In 1967 Shell held a conference on stratigraphic traps at its Denver regional office. I attended the meeting as a representative from the Shell Development Research Laboratory. Also in attendance was AAPG Honorary member Bert Bally, who at the time was the manager of exploration research at the laboratory, and Jim Hohler, the manager of exploration operations from the head office in New York City.

The remainder of the room was filled with Denver office exploration staff members.

During the conference, presentations were made on 24 separate stratigraphic traps for consideration as seismic research projects for the lab or for additional exploration efforts by the Denver office.

At this time a convergence of events smiled on Pete and his ideas. Pete’s former district manager, AAPG member Reed Peterson, still thought enough of Pete’s ideas about the Michigan Basin to invite him back to again present his ideas.

In addition, the newly appointed exploration manager, Jerry Pirsig, was not only a geophysicist, but since he was from Shell Canada, had experience in obtaining usable seismic data in areas of thick glacial drift. Furthermore, a new play starting in 1965 had developed in Canada – the Rainbow Reef Trend, in which prolific oil fields had been discovered in Devonian pinnacle reefs surrounded by thick evaporites in a starved-basin setting.

This was an ideal analog to the Michigan Basin, and Pirsig knew that seismic had been used successfully to identify these reefs.

I still have a vivid memory of the conversation between Bert Bally and Jim Hohler on the post-meeting cab ride back to the airport. I was focused on which stratigraphic traps could benefit from research efforts at the laboratory; whereas all Bert and Jim wanted to talk about was what great potential the Michigan Basin Reef play had as a major opportunity for Shell.

The rest, as they say, is history.

Almost immediately, the Denver office assembled a dedicated staff of geophysicists, geologists, petroleum engineers and landmen focused on acquiring seismic data, land and potential drill sites along the fairway Pete had identified.

Shell drilled its first discovery on a pinnacle reef in along the fairway in 1969, and continued with a very successful exploration and development program in the area.

Today, more than 500 individual pinnacle reef fields have been found along this fairway. As noted by AAPG Honorary member, past president and Sidney Powers Award winner Marlan Downey, who presented a summary of Shell’s success in this play in the March 2000 EXPLORER, this play still stands as the most profitable single onshore play for Shell over the last 50 years. Cumulative production today stands at 410 million barrels of oil and 2.4 TCFG.

The accompanying map shows the location of Pete’s original fairway with the productive reef trend superimposed. The correlation is rather amazing.

Pete Lucas went on to have a very successful career with Shell. When he retired in 1991, he was the general manager of exploration and production research for Shell Development Company.

When I attempted to contact Pete to let him know about this article, I was saddened to learn about his recent passing away (January 2012). He left behind a great legacy of creative thinking for those of us in the exploration business.

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