Snake Bit At Culebra Bluff

Abstract On January 3, 1977, the South Culebra Bluff Unit Well No. 1, a Morrow test in Eddy County, New Mexico, encountered an abnormally pressured zone in the Atoka formation and blew out. This paper reviews the circumstances surrounding the blowout, concentrating on those engineering considerations which permitted an eventual safe and efficient kill, permitted an eventual safe and efficient kill Introduction A blowout invariably has its unique circumstances, and each such occurrence entails an approach dictated by these circumstances, The South Culebra Bluff Unit Well No. 1 (SCB 1) was no exception. When the well was brought under some degree of control, there were several questions and considerations which influenced the methods employed for the kill operation. The mechanical condition of the drill pipe, which had dropped about twenty feet in a gas filled hole, was unknown. The presence or absence of protective rubbers on the drill pipe and their protective rubbers on the drill pipe and their condition were unknown. The condition of the bit and the possible impairment of circulation through the jets were in question, as was the degree of fill from drilling debris. Each of these factors could influence the ability to kill the well by circulating down the drill pipe through the bit. The source of gas was not known for a certainty and there was a possibility that a small-volume but high-pressure zone had caused the initial blowout while a lower zone contributed the large volumes of gas observed. The presence of zones of relatively low fracture gradient exposed in the open hole section was important, as this limited the weight of fluid which could be used for the kill. The continuing stability of six thousand feet of open hole was important, and needed to be monitored. Resolution of these problems (and others) was needed in order to determine a preferred kill method and a range of alternatives should the preferred method be preempted by actual conditions in preferred method be preempted by actual conditions in the well. During the kill operation we wanted no surprises for which we were not prepared. This paper details how each of these factors was measured or monitored, and a kill procedure with a high probability of success was designed. The approach herein is approximately chronologic and is subdivided into five parts: The Blowout, The Evaluation Phase, The Blow Down Phase, The Kill, and The Clean Up. THE BLOWOUT The South Culebra Bluff Unit Well No. 1 was spudded November 6, 1977, at a location approximately two miles east of Loving, New Mexico, in the southeast quarter of Section 23 (see Figure 1). "Culebra" is a Spanish word meaning "snake," "a violent disturbance in the midst of a quiet gathering," or "a practical joke." The name was prophetic, but the first definition above was prophetic, but the first definition above was generally accepted as applicable to this well. Intermediate casing 9 5/8 in. diameter was set at 6355 feet and cemented to the surface. Drilling proceeded without incident towards the Morrow proceeded without incident towards the Morrow objective. One drill stem test was attempted in the Bone Springs formation at 6956 feet but recovered drilling mud only. At 11,754 feet the well encountered a sharp drilling break from 5 minutes per foot to about one-half minute per foot. The bit was pulled off bottom at 11,769 feet, when the well kicked. It blew out, caught fire, and burned out of control. Shortly after the blowout the drill pipe slipped from the blowout preventers allowing it to fall some twenty feet into the gas-filled hole. In the afternoon of January 4th the Red Adair crew arrived on location.