WorldWide Drilling Resource

Frequently-Used Geological Terms Part 58 Glossary Adapted from the Dictionary of Geological Terms O Onyx - A variety of chalcedony which is like banded agate in consisting of alternating bands of different colors but unlike it in that the bands are always straight and parallel. Onyx Marble - A compact, usually banded, generally translucent variety of calcite, or occasionally aragonite, resembling true onyx. It is usually deposited from cold water solutions, often in the form of stalagmites and stalactites in caves. Oölite - A sedimentary rock, usually a limestone, made up of oöliths cemented together. Oölith - One of many small rounded bodies in a sedimentary rock resembling fish eggs. It is generally formed of cal- cium carbonate, in layers around a nu- cleus such as a grain of sand. Opal - A mineral consisting of packed spheres of silica. Opal occurs in most colors, is transparent to nearly opaque.It is deposited at low temperatures and is found in a wide variety of rocks and forms. The transparent colored varieties showing opalescence are valued as gemstones. Opalescence - A milky or somewhat pearly appearance or luster of a mineral, like that shown by opal and moonstone. Oil Wells Using HDD are Among the Highest Producers Adapted from Information by the U.S. Energy Information Administration Commercial use of horizontal directional drilling (HDD) began in the 1980s. Since then, enhanced drilling techniques have improved the process and it has become a more common practice in the oil and gas industry. HDD is currently used in some of the highest producing wells in the country. Typically, geologic formations are greater in horizontal extent than they are in vertical thickness. For this reason, more oil-bearing rock is exposed for production in horizontal drilling than in vertical drilling. HDD wells are often completed in combination with hy- draulic fracturing to maximize production along the exposed rock formation. The U.S. Energy Information Administration estimates two-thirds of U.S. natural gas production comes from hydraulically fractured wells. In 2015, nearly 77% of the most prolific U.S. oil wells, or those producing more than 400 barrels of oil equivalent (BOE) per day, were horizontally drilled. For about 85,000 moderate-rate wells pro- ducing in 2015, defined here as more than 15 BOE per day and up to 400 BOE per day, 42% were drilled horizontally. Of the approximately 370,000 lowest rate, marginal oil wells in 2015, also known as stripper wells, only about 2% were horizontal wells. Look for more terms next month! WWDR photo of opals. 28 FEBRUARY 2017 WorldWide Drilling Resource ®