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Marcellus Issues in West Virginia: An Introduction

Well Construction

Natural gas wells are constructed so that there are barriers between the environment and fluids from underground, fluids used for drilling and fracturing a well, and the gas being produced. These barriers take different forms depending upon which stage of construction a well is in.

The Site

Before we discuss barriers it's best to look at a drill site to note the main features. The most obvious is the drill rig that is present while the well is being drilled. Supporting the drill rig are structures for offices, chemicals, and equipment. There is a vessel holding diesel which powers the rig and other equipment. There will be water storage which can be in tanks or pits. And there will be stockpiles of the various sizes of casing used in the well.

EQT drill site

The drill site during fracturing changes somewhat. The rig will be gone as will be the unused casing. There will still be chemical storage, equipment and usually an office. Diesel is used for the pumps . During fracturing there might be sand and water stored on site.

The site will change again when fracturing is completed. A special type of rig might be brought in to remove fracture plugs and put in tubing after flowback has been collected and removed from the site.

Finally, the well will be readied for production with a special wellhead sitting on top of the casing which controls and directs the produced gas. The pad will be almost empty with production facilities installed that include separators and driers for removing liquids from the gas and large tanks to store the liquids. Some pads have small compressors which push the gas through a pipeline.

Protective Barriers

When a well is being drilled the barriers that protect the environment are varied. There's a blowout preventer once casing has begun to be installed. The casing itself and cement between casing and the edges of the drilled hole are intended to seal off and protect groundwater and to prevent gas producing formations, above the Marcellus or other productive formation, from affecting the environment. While the well is being drilled the drilling fluid (or mud) itself acts as a barrier, helping prevent blowouts.

Before fracturing, after the production casing has been installed, the blowout preventer will be removed. A special fracture T will be placed on the casing. The production casing will be perforated using explosive charges at predetermined intervals. A multistage fracturing operation will have fluid pumped at high pressure through the perforations into the formation creating much larger and deeper fractures. A fracture plug will be installed. The plug can be either mechanical or a special solidifying product like tallow. This group of operations (perforations, fracturing, and plugging), will take place repeatedly along the horizontal lateral from the end of the lateral toward the beginning until the final plug is installed.

After the well has been fractured, the fracture T will be removed, and the blow out preventer will be reinstalled. The fracture plugs will be either removed mechanically or by drilling through them and flowback will be released in a controlled manner. The well will produce flowback (a high pressure mixture of natural gas, proppant, and chemicals) for days.

Once the flowback has diminished to a satisfactory level, production tubing is installed, the blowout preventer will be removed, and a special wellhead fixture will be installed to control the high pressure natural gas being produced by the well.

At each stage of well construction there should be two barriers between the natural gas, and produced fluids, and the environment.

The next page will look at these barriers more closely and how they can fail.


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