Onshore Drilling

Onshore Drilling

Source: ChevronTexaco Corporation Drilling into the Earth in the hopes of uncovering valuable resources is nothing new. In fact, the digging of water and irrigation wells dates back to the beginning of recorded history. At first, these wells were primarily dug by hand, then by crude stone or wood tools. Metallurgy brought about the use of iron and bronze tools to delve beneath the Earth's surface, and innovations led to more efficient ways of removing debris from the newly dug hole. The first recorded instance of the practice of 'drilling' holes in the ground came about around 600 B.C., when the Chinese developed a technique of repeatedly pounding bamboo shoots capped with metal bits into the ground. This crude technology was the first appearance of what is now known as 'percussion drilling'; a method of drilling that is still in use today. Much advancement has been made since these first bamboo drilling implements, with the realization of the value and increased demand for subsurface hydrocarbons. This section will cover the basics of modern onshore natural gas drilling practices. There are two main types of onshore drilling. Percussion, or 'cable tool' drilling, consists of raising and dropping a heavy metal bit into the ground, effectively punching a hole down through the Earth. Cable tool drilling is usually used for shallow, low pressure formations. The second drilling method is known as rotary drilling, and consists of a sharp, rotating metal bit used to drill through the Earth's crust. This type of drilling is used primarily for deeper wells that may be under high downhole pressure. Cable Tool Drilling Cable tool, or percussion drilling is recognized by many as the first drilling method employed to dig wells into the Earth for the purpose of reaching petroleum deposits and water. This method is still in use in some of the shallow wells in the Appalachian Basin, although rotary drilling has taken over the bulk of modern drilling activities. The basic concept for cable tool drilling consists of repeatedly dropping a heavy metal bit into the ground, eventually breaking through rock and punching a hole through to the desired depth. The bit, usually a blunt, chisel shaped instrument, can vary with the type of rock that is being drilled. Water is used in the well hole to combine with all of the drill cuttings, and is periodically bailed out of the well when this 'mud' interferes with the effectiveness of the drill bit. Early Percussion Rigs in Pennsylvania - Late 1800's Source: Office of Fossil Energy, DOE Cable tool drilling has historically taken many forms. In the early days of percussion drilling, equipment was very crude compared to today's technology. The 'springpole' technique, used in the early 1800's, consisted of a flexible pole (usually a tree trunk) anchored at one end, and laying across a fulcrum, much like a diving board. The flexible pole, or springpole, would have a heavy bit attached at the loose end. In order to get the bit to strike the ground, workers would use their own body weight to bend the pole towards the ground, allowing the bit to strike rock. The tension in the pole would spring the bit free, should it become stuck in the ground. Much advancement has been made since these early percussion rigs. In fact, it was from cable tool drilling that one of the most important drilling advancements was made. In 1806, David and Joseph Ruffner were using the springpole technique to drill a well in West Virginia. In order to prevent their well from collapsing, they used hollow tree trunks to reinforce the sides of the well, and to keep water and mud from entering the well as they dug. They are credited as the first drillers to use a casing in their well - an advancement that made drilling much more efficient and easily accomplished. It is believed by many that 'Colonel' Drake's 1856 well achieved success due to the use of steel casing to reinforce the well. Drake's well was drilled using steam powered cable tool drilling methods. A Modern, Mobile Cable Tool Drilling Rig Source: Anadarko Petroleum Corporation Innovations, such as the use of steam power in cable tool drilling, greatly increased the efficiency and range of percussion drilling. Conventional man-powered cable tool rigs were generally used to drill wells 200ft or less, while steam powered cable tool rigs, consisting of the familiar derrick design, had an average drilling depth of 400 to 500 feet. The deepest known well dug with cable tool drilling was completed in 1953, when the New York Natural Gas Corporation drilled a well to a depth of 11,145 ft Source NaturalGas.org.