![]() This is done by drilling in a direction that intersects a maximum number of fractures. If the well is drilled perpendicular to the plane of these fractures, then a maximum number of fractures will be penetrated.ĭ) Improve the productivity of wells in a fractured reservoir. In many geographic areas, there is a dominant fracture direction along which most of the fractures are aligned. These fractures form naturally and can be an important route for the collection of fluids (water, natural gas, oil, geothermal fluids) held within the rock, and the movement of those fluids to wells or outcrops. When combined with hydraulic fracturing, horizontal drilling can convert unproductive shales into fantastic reservoir rocks.įractured Reservoirs: Many subsurface rock units have "sets" of parallel fractures that are vertical or near-vertical. This longer pay zone will usually result in a significant productivity increase for the well. However, if the well is turned and drilled horizontally through the rock unit for five thousand feet, then that single well will have a pay zone that is five thousand feet long. If a rock unit is fifty feet thick, a vertical well drilled through it will have a pay zone that is fifty feet in length. Many horizontal wells in natural gas source rocks have over one mile of pay zone penetration.Ĭ) Increase the length of the "pay zone" within the target rock unit. ![]() Maximize Pay Zone: If a vertical well is drilled through a 50-foot-thick reservoir rock, then natural gas or oil can seep into the well through 50 linear feet of "pay zone." However, if the well is turned to horizontal (or the same inclination as the rock unit) and drilled within that rock unit, then the distance of penetration within the pay zone can be much greater. (C) Increase the length of the "pay zone" This method significantly reduced the footprint of natural gas development within the campus area. Over a 25-year lifetime, the wells are expected to produce a total of 110 billion cubic feet of gas. In 2010, the University of Texas at Arlington was featured in the news for drilling 22 wells on a single drill pad that will drain natural gas from 1100 acres beneath the campus. This method has been used to reduce the surface footprint of a drilling operation. See graphic (A) - at the top of this page - to learn how the Pittsburgh International Airport will be paid $500 million for their gas. This reservoir might still be tapped if the drilling pad is located on the edge of the property and the well is drilled at an angle that will intersect the reservoir. Sometimes a reservoir is located under a city, airport, or park where drilling is impossible or forbidden. These six purposes are described below and graphically illustrated by the six drawings on this page.Ī) Hit targets that cannot be reached by vertical drilling. ![]() Horizontal drilling has been used for many purposes, which include:Ĥ) improve production in fractured reservoirs Examples are the Marcellus Shale of the Appalachian Basin and the Bakken Formation of North Dakota. When horizontal drilling is combined with hydraulic fracturing, some rock units which were unproductive when drilled vertically can become fantastic producers of oil or natural gas. In these cases, an ability to accurately steer the well in directions and angles that depart from the vertical is a valuable ability. However, drilling horizontally or at an angle other than vertical can obtain information, hit targets, and stimulate reservoirs in ways that cannot be achieved with a vertical well. Most wells drilled for water, oil, natural gas, information or other subsurface objectives are vertical wells - drilled straight down into the earth.
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