Oil and natural gas is formed when organic material derived from the breakdown of plants and animals is included in sedimentary deposits. Over time, the sedimentary deposits change to rock, and the included organic material gets changed into fossil fuel as either coal, oil, or natural gas. The type of fossil fuel that is developed depends on both the original composition of the organic material and the temperature and pressure that it has been exposed to, deep in the earth.
Shale oil and gas is defined as oil and natural gas, respectfully from a fine grained rock known as shale. The shale acts as the source, reservoir and seal for the oil and natural gas. Wells are primarily horizontal and are stimulated to produce oil and gas by hydraulic fracturing. Only shale formations with certain characteristics will produce oil and gas. The most significant trend in U.S. oil and natural gas production is the rapid rise in production from shale formations. Shale oil and gas deposits are usually classified as “continuous” type gas accumulations often extending throughout large areas. This means once the resource is proven in an area low risk development is possible over a large area.
A key element in the emergence of shale oil and gas production has been the refinement of cost-effective horizontal drilling and hydraulic fracturing technologies. These two processes, along with the implementation of protective environmental management practices, have allowed shale oil and gas development to produce from previously unproductive areas.
Technology drives the exploration and production of shale oil and gas which is comprised of either vertical or horizontal wells. In both cases, fresh water aquifers are protected by the use of casing and cement effectively isolating them from the deeper intervals. Most shale oil and gas plays involve horizontal well completions to optimize recovery and well economics. Horizontal drilling has a big advantage over its vertical cousin, in that a large amount of the wellbore can come into contact with the reservoir. This also means that far fewer wells need to be drilled and the wells that are drilled can have many wells drilled from the same well pad site thus reducing surface impact.
The second critical element to the success of shale oil and gas exploration and production is the use of hydraulic fracturing. This process involves the injection of mainly water and sand, or a similar “proppant” into a shale formation to generate fractures or cracks in the target rock formation. The sand or proppant holds the fractures open so that the oil and gas in the shale can flow to the wellbore and thus be produced. The fluid, or fracture fluids, are mainly comprised of water and sand with a small balance consisting of additives that improve the efficiency of the fracture process. The particulars of each hydraulic fracture are based on the specifics and characteristics of the rock formation in question.
At the completion of the drilling and fracturing process, the water used in the fracture stimulation process is produced back along with the oil and natural gas. This water requires management to protect surface and ground water resources, and ideally reduce future demands for fresh water. Stakeholders including local and federal governments and shale oil and gas operators look for ways to “Reduce, Re-use, and Recycle” in order to minimize the impact on the environment and the community. Water treatment technologies have been developed for use on shale oil and gas produced water so that it can be re-used.