|
This paper outlines the development of a nitrogen drilling system used by Meridian Oil on three nitrogen drilled horizontal wells in the San Juan Basin of New Mexico. The nitrogen drilling system eliminates the downhole fire risks associated with air drilling in hydrocarbon producing formations while significantly reducing costs as compared to pipeline gas (methane) drilling or trucked liquid nitrogen drilling. Typically, wells that must be gas drilled through productive intervals rely on pipeline gas, expensive trucked liquid nitrogen, or air-water injection (mist) systems. Water mist injection minimizes downhole fire potential but this method is unacceptable on horizontal wells as the extended drilling time in producing intervals greatly increases the probability of downhole fires. Data will be presented which outline the parameters for the nitrogen drilling system development including the required flowrates, the allowable oxygen concentrations, and economic analysis and justification. Actual field data will be presented, providing additional information relating to safety enhancements, cost reduction, and additional upside through the use of the nitrogen drilling system. In an effort to eliminate lost circulation problems and minimize formation damage, air, air-mist, and pipeline gas are used extensively as drilling media in under-pressured reservoirs. Certain areas in the San Juan Basin of New Mexico must be drilled with gaseous systems due to severe lost circulation. While in many cases atmospheric air may be used as a low cost gas for drilling, air is not suitable when hydrocarbon zones are traversed. With the addition of hydrocarbons to the air drilling system, all of the elements necessary to initiate combustion are present. To minimize the risk of downhole fires, common drilling practice dictates switching to an air-mist system or using pipeline gas to drill through the gas producing interval. The use of misting agents reduces the possibility of ignition, while the use of pipeline gas results in a system that is fuel rich and thus unable to sustain combustion. Pipeline gas is an effective way to avoid downhole fire problems, however the costs associated with it make it uneconomical to use in many applications. The extended drilling times in producing formations and the additional downhole tool costs make horizontal drilling with air or air-mist systems a very risky operation. Many operators in the San Juan Basin of New Mexico and the Weyburn Field in Canada have experienced downhole fire problems while directionally drilling with air-mist and aerated mud systems. In Canada a number of operators have begun using trucked liquid nitrogen to create a nonflammable aerated drilling fluid. In the San Juan Basin many of the operators rely on the readily available pipeline gas for their gas drilling requirements. Both of these methods of gas drilling are inherently expensive and dangerous. in an effort to lower drilling costs and improve operational safety on gas drilled directional wells, Meridian Oil assisted in the development of a nitrogen drilling system. This system removes the oxygen from atmospheric air, thus yielding variable degrees of pure nitrogen gas without the cryogenic equipment and cost typical of most nitrogen operations. |