A New Approach in Relief Well Drilling
Authors: Bruist E.H. 
Published: December 2007

Cox No. 1, during coring operations in the high-pressured, sour-gas Smackover formation at 21,000 feet, blew out and caught fire. An intermediate-depth relief well was drilled to intersect and parallel the wellbore over a 100-foot interval. By perforating to establish interwell communication, and then pumping in a large volume of heavy cement slurry at high rates, the wild well was killed and permanently plugged. plugged. Introduction

The Shal Cox et al. No. 1, a 22,000-ft Smackover exploratory test, was located near Piney Woods in Rankin County, Miss. Because of the possibility of encountering high-pressured sour gas and the well's proximity to the Piney Woods Country Life School, proximity to the Piney Woods Country Life School, elaborate safety measures and contingency plans had been prepared in case of a blowout. When the well actually blew out and caught fire (see Fig. 1) on March 25, 1970, all persons within a 3-mile radius were safely evacuated. There was one earlier fatality; a member of the drilling crew died during the attempts to regain control of the well just before the blowout. The exact cause of his death was not determined.

Calculations and information gained from H2S and SO2 monitors established within a few days that the concentration of these gases at no time would exceed the danger level beyond a distance of 1 mile from the blowout. All evacuees were returned to their homes, except for six families who lived within the 1-mile radius. These were housed in mobile homes at locations of their choice. As a safeguard, an 8-ft-high chain link fence with an approximate radius of 1 mile was erected around the burning well to prevent unauthorized persons from entering the area.

The first relief well, Cox No. 2, was spudded on May 3, 1970, at a surface location some 3,500 ft west of the blowout. This well was designed to be drilled straight to 9,000 ft, and from there directionally in a "straight" kick to 21,000 ft, to be bottomed close to the Cox No. 1 wellbore (see Fig. 2). There was considerable doubt about the effectiveness of this approach, since A raised several questions, such as:

- Would it be possible to drill a directional well below a vertical depth of 21,000 ft while maintaining directional control?

- What would be the maximum allowable distance between wells so that communication still could be established?

- Could fluids be pumped at rates sufficiently high considering friction losses, high reservoir pressure, and the nature of the reservoir rock to pressure, and the nature of the reservoir rock to kill Cox No. 1, which was flowing at high but undetermined rates?

Because of these uncertainties a special task force was formed to explore "novel" approaches. After a short, intensive investigation, it was suggested that it might be possible to drill a second relief well of intermediate depth, to be located about 1,000 ft from the blowout. This well would converge with and then parallel the Cox No. 1 wellbore for some vertical parallel the Cox No. 1 wellbore for some vertical distance in a depth range between 9,000 and 13,000 ft ( Fig. 2). If the wellbores would be adjacent interwell communication could be established by perforating, and Cox No. 1 would be killed by directly perforating, and Cox No. 1 would be killed by directly pumping mud or cement into it. If, on the other hand, pumping mud or cement into it. If, on the other hand, the wells would remain separated by several feet of formation, a cavity could be washed out in the relief well.

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