Successful Relief Well Drilling Utilizing Gyroscopic MWD (GMWD) for Re Entry into an Existing Cased Hole

Abstract

In late 2007, a blow out occured in a well in the Gulf of Mexico. The blow out was caused by a leak in the production casing, which broached the surface and caused the well structure to collapse. This SPE paper describes how the Apache Corporation utilized the latest state of the art Gyroscopic Measurement While Drilling (GMWD) tools to drill a relief well to stop the blow-out. The S-shaped relief well was drilled towards the blowout- well to perform a planned wellbore intersection. When reaching the blow out well, the production casing was milled and kill weight mud was pumped. This action stopped the blow out and enabled the operator to regain full control over the wellbore. This paper also emphasizes the challenges while drilling this re-entry well: A 800 ft portion of the relief well had to be drilled with a closure distance of less than 40 ft to the pilot hole. Conventional MWD drilling systems which base their measurements on earth's magnetic field are incapable of providing reliable readings in areas with magnetic interference. Proximity to casing hinders the ability of conventional MWD tools to function and therefore, a drilling BHA with an integrating rate GyroMWD (GMWD) was deployed in this well. Rate gyro measurements are based on the earth's spin axis and can provide accurate real time survey data, including true north toolface and azimuth where earth's magnetic field is distorted. This paper details an efficient way to drill a relief well and focuses on the innovative GyroMWD (GMWD) instrument that works in magnetic environments and close to metal casings. Introduction A relief well is drilled when the original well becomes inaccessable, the well is still flowing and the well has to be intersected from subsurface to perform kill operations and to re-gain well control. Although relief well drilling is rare, the need for them has recently increased in the Gulf of Mexico. Hurricanes have grown more powerful and more frequent in recent years, leaving more damaged surface structures and inaccessable wells behind. Additionally, the average age of producing wells is at a record high, and the industry faces an increased risk of casing corrosion and breakage. The latter is what happened in a well in the Main Pass field (GOM): A leak in the production casing broached the surface and caused the wellbore structure to collapse. To control the blow-out, a relief well would have to be drilled to intercept the blow out well from subsurface. Pumping kill mud as soon as communication to the blow out well is established would be the solution to stop the well from flowing. Wellbore position uncertainty The key to successfully intercepting a target well is to overcome unkowns in the positions of both, the target well and the relief well itself. Genenerally the deeper a well, the larger the elipse of uncertainty and the more difficult it is to perform a planned interception of another well. Existing surveys from a target well can be off by several feet whereas the accuracy of a few inches is actually needed to hit another wellbore. That is why the difficulty while drilling into a target well is usually to "find" the target well at a certain subsurface depth. Often the full value of a quality, fit for purpose survey program is not realized until an unforeseen event occurs.