DEVONIAN DUNDEE FORMATION, CRYSTAL-FIELD, MICHIGAN BASIN - RECOVERY OF BYPASSED OIL THROUGH HORIZONTAL DRILLING

Carbonate reservoirs of the Devonian Dundee Formation represent the mo st productive interval in the Michigan basin, yet have suffered widesp read abandonment due to improper early reservoir management and comple tion practices. Dundee carbonate reservoirs, deposited in marginal-mar ine and shallow-marine environments, have produced over 351 MMbbl oil from 137 fields, most of which were discovered in the 1930s and 1940s. initial potentials for many Dundee wells ranged from 2000 to 9000 bbl /day, presumably due to high permeability fractures and solution-enhan ced porosity in some areas and excellent primary interparticle porosit y in other areas. Crystal field, discovered in 1935 at a depth of less than 3500 ft (1060 m), was aggressively developed and produced at hig h rates, causing widespread water coning, such that 95% of the field w as drilled and abandoned in less than 5 yr, leaving considerable inter well reserves in the ground. No cores or wireline logs existed for the field prior to 1995, when the field became the subject of a multiyear study aimed at determining the feasibility of employing horizontal dr illing to recover bypassed reserves. A vertical test portion of the TO W 1-3 horizontal well, located in a structurally elevated portion of t he field, cored and logged the entire reservoir interval, yielding cru cial new information. On the basis of relevant data, a horizontal leg was drilled, resulting in an excellent producer with estimated recover able reserves of 200,000 bbl, Two subsequent horizontal tests with poo r results were drilled in downdip locations and oriented perpendicular to the TOW: well, suggesting the importance of both structural positi on and azimuth. Selective use of horizontal drilling is considered an appropriate, cost-effective means for recovering bypassed reserves in Dundee fields where sufficient geologic data exist to adequately chara cterize the reservoir and oil occurrence. For some fields, this may re quire new coring and logging operations.