A simulation approach was used to determine the gas loss from a storage field after a well got out of control during a replugging attempt. Because the event occurred in a storage field which has over 250 active wells, a smaller portion of the reservoir surrounding the problem portion of the reservoir surrounding the problem well was selected for reservoir simulation. The movement of gas into the smaller portion of the reservoir from the rest of the reservoir was simulated by using pseudo injection wells in the model.
The pseudo wells were placed at the grid boundary where gas migration was expected to occur. Wells surrounding the incident well were shut-in for pressure observation throughout the event and were included as observation wells in the model. By assuming different injection rates in the pseudo wells with various assumed loss rates from the incident well, a good history match was obtained. From these studies, an accurate estimate was made of the natural gas lost during the 16 day incident.
The Taggart Storage Field (originally called the Six Lakes Field) was discovered on May 11, 1934 at a wellhead discovery pressure of 513 psig. The field was developed on 40 acre spacing. By March 1, 1936 there were 75 gas wells and ultimately there were 224 producing gas wells. The largest gas well had an initial gas flow potential of 112,000 MCF per day.
The reservoir is the "Stray Sandstone" unit in the Michigan Formation of late Mississippian Age. The reservoir is a structural trap (Fig. 1) in a porous and permeable sandstone that can be correlated for many miles across Michigan. Porosity of the sandstone ranges from 15–23% and Porosity of the sandstone ranges from 15–23% and permeabilities are as high as 1000 millidarcies. permeabilities are as high as 1000 millidarcies. The reservoir is approximately 1300 feet deep and has a maximum gross thickness of 50 feet (Fig. 2).
By March 12, 1953, the Taggart Field had produced 51.3 BCF and was essentially depleted. produced 51.3 BCF and was essentially depleted. All but 64 of the original 224 gas wells had been plugged and abandoned, due to water encroachment. plugged and abandoned, due to water encroachment. Michigan Consolidated Gas Company had completed acquisition of mineral interests and storage rights at that date. The company then started to develop the field for underground gas storage. It was necessary to reopen all of the plugged and abandoned gas wells and to convert them to facility wells with new casing or replug them to prevent leakage. prevent leakage. Many of the old wells had both the surface and production casing shot off or ripped when they were abandoned. This made it difficult to locate them. As of 1974 there remained thirty five wells to be replugged. Twelve of these wells had been relocated with a Casing Finder Tool. One of these 12 wells, the S. L. #375, was plugged in 1949.