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78 In the United States, which in 1920 supplied 65% of the world's production, it is generally estimated that from 25% to 40% of current output is " flush " production; that is, production from the large initial flow of new wells, which subsequently would decline to moderate " settled " production or become exhausted. There were about 35,000 new wells completed in the United States in 1920; 24,000 of them were rated as oil producers. At the end of that year there were 7,200 wells drilling and 2,100 rigs erected or building for drilling. The number of wells producing oil in the United States, Oct. 31 1920, was 258,600. The average per well was 4-9 barrels.

The principal drilling systems are: (l) percussion, which includes the standard cable tool (American system) and the pole tool (Cana- dian system); (2) hydraulic rotary system; (3) combination system; (4) hydraulic circulating system (see 21.319). In the Appalachian region of the United States wells are sunk by the standard or churn system, with a modified light rig, and range in depth from a few hundred feet to 3,*oo or 4,000 feet. In many sections groups of wells are pumped from the central station. The yield of wells in the Appalachian field is small, the average for Pennsylvania being about 0-3 bar. per well; New York, p-2 bar.; Kentucky, 3-1 bar.; W. Vir- ginia, I-l bar. ; and eastern Ohio, 0-8 barrels. Wells in the mid-conti- nent field are generally drilled by standard tools. The cable system is used in central Texas, and the rotary system in northern Texas and in some districts of Oklahoma. The rotary system exclusively is used in northern Louisiana. The depth ranges from 200 ft. to 3,500- ft., drilling in recent years averaging more than 2,000 ft. Recoveries per acre from mid-continent pools have been generally higher than in the eastern fields, but less than in the Gulf coast and California. The average production per well in Oklahoma and Kansas is 6 bar.; northern Texas, 31-6 bar.; central Texas, 22-9 bar.; and northern Louisiana, 31-6 barrels. The rotary method is used exclusively in the Gulf coast field, the depth of wells ranging from 1,000 to 3,500 ft., and the production per well being 34-6 bar. in coastal Louisiana and 49-7 bar. in coastal Texas. In the Rocky Mountain field the standard and rotary systems are used, the shallow districts of this field also being largely drilled by the standard cable system with the portable rig. The depth of the wells ranges from 1,000 to 3,500 feet. The average production per well is 55-9 barrels. In California drilling is about evenly divided between the standard and rotary systems. The combination rig is also extensively used, and there is some drilling by the hydraulic circulating system. Well-depths range from 1,000 to 3,500 ft. and the average production per well is about 32-3 barrels. A well of average depth in the mid-continent field could be drilled and equipped for less than $13,000 in 1913. In 1915 the cost increased to about $14,000; in 1918 to $24,000; and in 1920 to about $32,000. A factor in the advance in cost was the increased depth of the average well. Drilling cost of an average well in central Texas in 1920 was from $44,000 to $68,000 ; in certain Gulf coast pools, $39,000; while in the Rocky Mountain and California fields it has risen above $100,000 per well.

In Mexico, where the wells usually have a great initial production and where the yield of individual wells is often restricted only because of inadequate marketing facilities or as a precaution against water inroads, the percentage of current production that might be termed " flush " is much higher than in any other producing country. Mex- ico's production is obtained from comparatively few wells. The country was credited on Jan. 31 1921 with 367 producing wells, but it is estimated that the bulk of the 1920 production of 163,000,000 bar. was obtained from about 200 wells. The wells average about 2,000 ft. in depth. In the Tehuantepec field the wells have been of shallow depth and short-lived. Drilling in Mexico is about evenly divided between the rotary and standard cable system, and the hydraulic circulating system is used to some extent.

The Canadian pole tool system is used in Canada, while the deeper drilling in the Calgary district has been done by the standard cable system and there has also been some rotary drilling. Wells in the Petrolia district, Ontario, are about 500 ft. in depth and yield from 5 to 25 bar. a month. The standard cable system is principally used in Venezuela, although there has been a good deal of drilling with the rotary method, and a combination of both. Wells in the Mene Grande fields range from 600 to 1,700 feet. Wells in Colombia have been drilled by the cable system and combination cable and rotary, the depth being 1,700 to 2,300 feet. In Peru most wells in the Zorritos field are between 600 and 2,000 ft. in depth; in Labitos from 2,000 to over 3,000 ft.; and in Negritos the average is about 2,500 feet. The standard cable system of drilling is gener- ally used in Peru, but there has been some rotary drilling in the Zorritos field, where a total of 920 wells had been drilled up to 1919, the greatest number of producing wells at any one time being about 50. In Lobitos a total of 1 18 wells were producing in 1919; in Negri- tos 732 were active. Drilling in Argentina has been done by prac- tically all methods, but the one in most general use is the Galician pole tool system, which is a modification of the Canadian pole tool system, the equipment providing for a larger and heavier rig. The American standard cable system is also in use in Argentina and there is some rotary and also hydraulic circulating drilling. Production in 1919 was obtained from about 72 wells. In Trinidad wells range from 700 to 1,740 ft. in depth. Rotary drilling is used almost exclusively.

The Russian free fall system, a modification of the Canadian pole tool system, is used in Russia. In this, there is a free fall of the tools,

which are then picked up. The diameter of some of the Russian wells is unusually large, the starting diameter being in many cases 36-40 inches. In the Baku field the depth of the wells ranges from 2,000 to 2,500 feet. Baku wells are famous for their large initial flow and large total yield. In Galicia, as well as in Rumania, the Canadian pole tool system, modified and adapted, is generally used, but the hydraulic circulating system is also used. Galician fields require deep drilling, many wells in Boryslaw-Tustanowice being over 4,000 feet. The pole tool system is also extensively used in Rumania. Wells range from 1,000 to 2,500 ft. in depth, and in the Moreni district wells of great capacity have been brought in. The standard cable system with portable rig is used almost exclusively in Italy. The same system, without portable rig, is used in Persia, India and Egypt. The Galician pole tool system is used in the Dutch East Indies. Persian- production is obtained at from 1,100 to 1,400 feet. Deeper drilling was resorted to in the Yenangyaung field of Burma with good results, previous drilling not having exceeded 300 or 500 feet. Wells more than 2,000 ft. deep are drilled in the Singu field of India. Wells in Japan range from 600 to 2,000 ft., and the rotary system, introduced in the Akita field in 1913, is used almost exclu- sively. The diamond drill, a " core " drill used in prospecting for coal, iron and copper deposits, has been introduced as a geological aid in oil-field work. Another means recently employed for drilling test holes and shallow wells is a combination rotary, core and churn drill. Petroleum development of recent years has entailed deeper drilling with consequent heavier demand on oil-field materials. In the United States and in other countries the shallow fields have become ex- hausted. Drilling to 2,500 and 4,000 ft. has demanded sturdier equipment, heavier and larger casing and improved designs in drilling machinery. Better methods of handling heavy wrenches and bits and of dressing bits have been adopted.

New mechanical devices to aid in well-drilling are constantly being introduced. In electrical rotary drilling, an electric device keeps a check on the drilling crews, indicating when and how long the rotary was shut down. A register giving the weight of pipe resting on the bit is being perfected by experimental tests. It is designed to enable the driller to determine the amount of speed to use in certain formations, with a view to lessening " twist-ons " and thereby lessening the number of fishing jobs. While derricks in most oil- producing countries are chiefly of timber, the all-steel derrick has appeared in certain fields of the United States, Rumania, Galicia, Trinidad, England and South America. Electric power has become a factor in field work and has been adopted for the pumping of wells and for drilling, for driving slush, water, oil and vacuum pumps and for air compressors, gas extractors, machine shops, field lighting and dehydration of oil. Electric power has made advances in Texas, in California and in the mid-continent fields. It has been adopted in Rumania and in the Balakhany-Saboontchy-Romany-Surakhany area and the Bibi-Eibat field of Russia. Electrification of the Yenan- gyaung field of Burma has also been undertaken. The use of com- pressed air to increase oil extraction has been introduced recently in certain producing areas. The process consists of pumping compressed air or gas into some wells while others are pumped for oil. The advent of the internal-combustion engine has brought about the extended use of belt, chain and gear driven pumps, while previously single or duplex driven reciprocating steam pumps were mainly used. The turbine pump has also developed oil-field possibilities.

TRANSPORT AND STORAGE

Pipe Lines. With its large crude-oil production obtained from fields often far from refining and consuming centres, the petroleum industry of the United States has developed pipe-line systems of great mileage and capacity (see 21.320). In the fields themselves there are networks of gathering lines connecting the wells with main trunk lines and railways, the trunk-line systems connecting the fields with the refining centres. It is estimated that pipe lines in the United States totalled about 35,000 miles. Practically all of the crude oil produced (1,300,000 bar daily) is transported by pipe line, some of it only a few miles and some of it as far as 1 ,700 miles. About 150,000 bar. a day are taken from the eastern and mid-continent fields to the Atlantic seaboard through a connecting system of pipe lines. Mid-continent crude is also piped to the Gulf coast. It is estimated that the total U.S. production moves by pipe line an average of more than 500 miles. Pipe lines in Mexico have been constructed from the Panuco and Topila fields to Tampico and from the southern fields to Tampico and directly from the southern fields to the Gulf coast, where sea loading lines are installed. There is an international trunk line running into Canada connecting with lines in Ohio. In Venezuela the production in the Mene Grande field is run by pipe line about 35 m. to a refinery at San Lorenzo where there is also a terminal from which crude oil is barged to a refinery on the I. of Curacao. A pipe line of about 25 m. has been constructed from wells in the Colorado district of Colombia to a refinery at Barranca Bermeja on the Magdalena river. The Lobitos field in Peru is connected by pipe line to the port of Talara, 16 m. distant, where there is a refinery and a terminal for export ship- ping. Argentina has short field pipe lines. In Trinidad there are pipe lines from the Pitch Lake district to refineries at La Brea and Port Fortin and also from this field and the Tabaquite district to Claxton's Bay, where they extend into sea loading lines. Pipe lines