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Hydraulic fracturing is necessary for development of the Marcellus shale natural gas as this process opens up fractures in the shale which allow the natural gas to flow to the well. This operation involves injecting several million gallons of water, sand, and a small addition of chemical additives into the formation at high pressure. After the injection is completed, approximately 10-20 percent of the fluids (known as flowback) return to the surface via the well. Therefore, a 5-million gallon hydraulic fracture stimulation might return 500,000 to 1 million gallons of water. The reuse of the flowback fluids by the drilling industry for subsequent hydraulic fracture treatments significantly reduces the volume of wastewater being generated by hydraulic fracturing. This water can be treated and blended with fresh water and reused, which is what many companies are now doing to minimize the amount of water that would otherwise be potentially discharged to streams or rivers once treated.
Currently, new Pennsylvania Department of Environmental Protection standards dictate that any flowback must be treated to have a total dissolved solids (TDS) concentration of 500 parts per million, which is consistent with Pennsylvania drinking water standards, and therefore won’t increase TDS levels to unacceptable levels. There are new treatment plants being built to meet these standards and at least one is now in operation in Williamsport, Pa.
Each well requires approximately 3 to5 million gallons of fresh water. Therefore, impoundments are utilized to store this water at the site. The flowback (frac) water may either be stored in dedicated lined impoundments or in steel tanks so that it may be treated for reuse or for proper disposal. More and more companies are utilizing tanks for storage to avoid potential problems of seepage and spillage from frac water impoundments.
It really depends on the gas company’s drilling program plans. However a typical approach would involve mobilization of a smaller drilling rig to install the upper vertical section of the well where steel casing and cement are installed to protect groundwater resources. If the company is going to install multiple wells on the same pad, then the smaller rig would typically complete the vertical wells and then larger rig would follow up by drilling the deeper part of the well, including the horizontal section. Only one horizontal well is drilled from each vertical well. It is common for natural gas companies to initially install one well on a pad in order to avoid having the lease for that parcel of land expire, a term known as “held by production.” This allows the company to then return for additional drilling as their schedule allows and when the gas economics become more favorable.
The total time to drill each well is about a three to six weeks depending on the depth and length of the horizontal well, so if there are four wells on a well pad, you could expect the big rig to be there for about three to six months. The hydraulic fracturing is a separate process done after the vertical and horizontal sections of the well have been drilled, and typically occurs within a few weeks or months of the well drilling, dependent on the project schedule, and may take up to several days for each well to be hydraulically fractured.
The gas company must lay out their units as part of their well drilling permit. A typical unit is 640 acres, which is a square mile. However, it can be more or less area. One well pad per square mile would be a reasonable estimate, depending on how many wells are necessary to drain the gas from the formation. This well pad would likely require multiple wells (4 to 10 or more) off of the same pad to drain the gas within the unit, depending on the length of the well lateral.
There’s not currently a spacing order in Pennsylvania for Marcellus wells, which would dictate a distance between wells to ensure the gas is efficiently drained and not left in the formation. Current industry estimates suggest that each well could produce a total of 5 billion cubic feet of gas, and some estimate the Marcellus may contain 500 trillion cubic feet of recoverable gas, suggesting that approximately 100,000 wells will be necessary to produce the recoverable gas.
The well pad needs to be lit up for safety reasons, and drilling is usually a 24 hour/7 days a week operation because it is not easily stopped and started. The drilling of each well typically takes 3-6 weeks. Therefore, it would be expected that nearly continuous activity would occur on the well site during this period.
If companies are drilling and fracturing wells, then they would very likely have some pipeline infrastructure in place to take the gas to the market place. However, additional infrastructure will need to be built to keep pace with the production of gas.