Horizontal Drilling in the Northern Reef Trend of the Michigan Basin
Lester A. Pearce, Christine M. Hewitt, Lisa M. Corder, 2003. "Horizontal Drilling in the Northern Reef Trend of the Michigan Basin", Horizontal Wells: Focus on the Reservoir, Timothy R. Carr, Erik P. Mason, Charles T. Feazel
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For a company operating in a mature province, it is extremely important continuously to seek new ways to improve recovery from known hydrocarbon accumulations. As the mechanical process of drilling horizontal wells matured in the mid-1990s, Shell Western E&P Inc. (SWEPI) was quick to apply this new technology to just such a province, the Northern Silurian Niagaran Pinnacle Reef Trend (NRT) in the Michigan Basin. To date, SWEPI has drilled more than 60 horizontal wells in this trend, which accounts for more than 55% of all horizontal drilling in the NRT and continues to be the industry leader. Much has been learned in the past decade, and it appears that the application of lateral drainhole technology can be an effective tool in the NRT in the right geologic and reservoir situations.
SWEPI first attempted to apply horizontal technology to the NRT in 1987. Those early attempts failed mechanically because of the inability to maintain a horizontal path through a significant section of reef. In only one well, the Bancroft-Bisard 2–1, was a horizontal path achieved, and that lateral was less than 30 m (100 ft) in length. No further horizontal activity occurred until 1994, when a review of the decline curve from that well indicated that not only had there been a production increase of 30 BOPD after the lateral, but the rate of production decline had been reduced from 37% to 18%. It was estimated that an additional 100 MBO would be recovered from that well as a result of the lateral. This information, coupled with improvements in drilling technology and the knowledge that great improvements in production were being made worldwide by the application of lateral technology, caused SWEPI to initiate a new lateral program in the NRT.
Five major opportunity types were evaluated with horizontal wells. SWEPI’s first attempt, in 1987, was a large gas cap over a thin oil leg. This type has continued to provide the most consistently positive results, and it accounts for 47% of the total laterals drilled. The second-largest opportunity type, with 36% of the total, is the heterogeneous reservoirs. These opportunities closely resemble exploratory drilling in which the success rate is low but the risk capacity is high. Only two low-pressure reservoirs, which depend on pure gravity drainage, have been drilled. Neither was successful. Another type is the improved kh in a low-porosity reservoir. Although SWEPI has drilled only four, these can be profitable in certain circumstances. The most disappointing type has been the thin oil column over a large water leg. We have drilled three thin-oil-column horizontals with no successes.
Approximately 40% of the 55 horizontal wells that had been drilled by May 1998 were considered economically successful. Ultimately, SWEPI has forecast that the horizontals will recover an additional 3.4 MMSTBO and 5.7 bcfg.
Issues that remain a concern include lost returns, wellbore damage, vertical position of the lateral, and the application of laterals in settings that have been unsuccessful to date. Significant oil volumes remain in these environments. We are attempting to address some of these issues as the program continues to mature.
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Horizontal Wells: Focus on the Reservoir
This book provides an overview of the new technical approaches required for best use of horizontal and extended-reach technology in different reservoir situations. The volume is a selection from more than 50 papers presented at an AAPG/SPWLA Hedberg Research Symposium, “International Horizontal and Extended Reach Well Symposium: Focus on the Reservoir,” held in The Woodlands, Texas, on October 10 14, 1999. The 16 chapters describe horizontal and extended-reach wells and drilling programs in a variety of geologic settings all over the world.