The system of boring is percussive
The deepest actual boring, 1,160 meters
Fou Chouen, where natural gas wells are principally found,


Annales des Mines, vol. xix, 1891, describes in detail the brine and gas wells of the province of Sze Chuen, in western China. This produces annually, as nearly as can be estimated, there being no regular statistics, about 812,000 tons of salt, which is entirely derived from borings, the salt being accompanied in places by petroleum and natural gas, the latter being utilized for boiling down the brine. The most important centers of production are in a district about 80 square miles in extent, about 25 miles northwest of the town of Fou Chonen.  The geological structure of the district appears to be somewhat complicated, but, according to the author, a complete succession from Cambrian up to Tertiary and post-Tertiary strata, which is recognizable in the following order:
 Stratigraphy of the Sze Chizen gas fields, China. Meters.
 Yellow sandstone Tertiary 38 to 100
 Red sandstone--------------------------------------------------------
 Gray limestone------------------------------------------------------- 200
 Ferruginous oolite, often with bituminous springs at
 Blue and yellow sandstone, Lias 270
 At this level gas is found sometimes in small quantities.
 Bluish gray marl 330 to 600
 White limestone, Permian
These strata yield brine of a yellowish color and medium saturation (10 to 15 % of salt)
 Sandstone and limestone with coal Carboniferous.
 Brown shining shale Silurian.
 Green schist Roofing slates.

Dark colored brine, of the higher strength of 15 to 28 percent of salt, is found below the last mentioned strata at depths varying from 930 meters to 1,100 meters, as well as the most important gas springs. As a rule, the upper yellow brine bearing beds are not found in these deep borings.

The system of boring is percussive, the cutting tool and sliding piece weighing from 200 pounds to 300 pounds, being suspended by a rope, and lifted about 2 feet at a stroke, by a lever worked by groups of coolies acting as dead weight.  According to the depth, from two to eight men are required to lift the tool from twelve to fifteen times a minute, the gangs being relieved at intervals of ten minutes. The cutting tool has eight steel-faced teeth, but without grooves, so that the, detritus accumulates at the bottom of the hole. This is removed by a sludger, consisting of a cylinder of wood covered with deep notches arranged ladder wise, which is lowered into the hole and moved about by a jerking motion on the rope until the grooves are filled with the sludge.
   Usually a pit is sunk by hand to a depth of about 100 feet from the surface, and lined with blocks of stone before the actual boring is commenced. The diameter adopted is from 9 to 12 inches, which may be contracted to 6 or 7 inches when it is necessary to life the hole through loose ground.
 The grating tubes are either large bamboos bored out or are built up of half trunks of cypress trees fitted together by swallow tailed joints, which are covered by hempen cloth, water proofed with a paste of lime and oil. This first covering is protected by a close serving of cord, with a thicker layer of the cement over all, the total thickness of the structure being but little less than the diameter of the hole.  According to the nature of the ground, the length of these casing tubes may vary from 10 to 300 feet; but when more than 20 feet are required in one length, the high derrick must be provided. This is made up of two of timber 40 feet to 50 feet high, with two diagonal struts, and a multiplicity of guy ropes, the use of iron being restricted to a minimum.

As may be imagined, the progress of the work is very slow, varying from a few feet per day in loose ground to an inch or less on very hard rock.
Some of the deeper wells have taken from twenty to forty years in sinking, and have ruined several sets of adventurers in succession.

The deepest actual boring, 1,160 meters, has never yielded anything.
Some three or four holes are above 1,000 meters deep, but the greater number are between 530 and 930 meters, in the Tsze-liu-tsing group. In the Kong-tsin group they vary from 330 to 660 meters as the most general depth, the shallowest being about 200 meters.

The accidents to which the borings are liable and the method of remedying them are treated at length by the author, with illustrations of the tools employed from Chinese drawings. These are generally similar to those adopted in Europe; but the construction is very different in principle, bamboo and string entering very largely into their composition instead of metal.

As a last resource, the method of pulverizing a lost tool is adopted and carried out with incredible patience. The removal of a tool weighing 300 pounds, in this manner, required about five years continuous work, night and day, of thirty-two men, at a cost of about Y, 3,000.

The brine is brought to the surface by tubular buckets of bamboo, with a foot valve varying from 2 to 6 inches inside diameter, and from t6 to 140 feet in length.
For the latter size, used in the deepest wells, derricks for 90 to 120 feet are required, the highest in use being 164 feet. These are built up of beams of timber lashed together with bamboo ropes, and cost from Y8OO to Y1,000.

The bucket is lowered and lifted by a flat rope 20 millimeters and 5 millimeters thick, formed of slips of bamboo united by hempen cords winding upon a gin which is usually drawn by buffaloes, two, four, or six of these being required, according to the depth of the well; but in the shallower ones the lifting is sometimes done by a windlass worked by from two to six men treading fashion. The load upon the rope in the deeper wells in some cases exceeds 30 hundred weight, corresponding to a stress of 9 1/2 tons per square inch.

The quantity of brine raised at each lift varies from 116 liters (250 1/2 gallons) with the smallest bamboos, to between 620 and 950 liters (136 to 200 gallous) with the larger ones, and under the most favorable conditions from two to four lifts may be made per hoar, according to the depth. When the bamboo is raised to the surface, a cover is pushed over the top of the bore hole, the valve is lifted by the ladder with an iron hook, and the brine runs into a reservoir.

The product of the deep wells is very dark-colored, and often emits suphuretted hydrogen in sufficient quantity to be dangerous to the workmen about the top of the pits if it is incautiously inhaled. In addition to salt, some of the wells yield petroleum and gas in variable quantity; the former is skimmed off from the surface of the water after it has been allowed to settle in the reservoirs.

The product varies in quality from a pure white-burning oil to yellow, greenish, and black kinds of low illuminating power and giving much smoke.  All are, however, burned, as the Chinese have no knowledge of petroleum refining.

The wells being generally away from the salt works, the brine is carried to the latter either by hand, when the journey is short, or by conduits made of bamboos, with chain and bucket-lifting wheels for overcoming intermediate differences of level, when a greater distance has to be traversed.
   The boiling down is done in shallow cast-iron pots about 4 feet in diameter, and 1.7 inch deep in the center.  The thickness varies from 11 inch in the center to 1 inch at the edges, and the weight is about 1,000 pounds.  The heating may be done by straw, wood, coal, or natural gas. The operation lasts from twelve to twenty-four hours, according to the intensity of the fire, and yields about 100 pound,; of salt.

In the district of Fou Chouen, where natural gas wells are principally found, from 600 to 1,200 pans may be heated by a single well. The principal supply is obtained from depths of not less than 670 meters. It is manly marsh gas, being less carburized than that obtained at shallower levels, which burns with a tolerably white flame, but is only got in small quantities.
  The top of the well is enclosed to a depth of 10 feet by a wooden casing, as nearly tight as possible and the gas is led by bamboo pipes into cemented reservoirs with dented roofs formed by inverted salt parts. From these reservoirs, the distribution of the gas is effected by means of bamboos leading to the pans, a short length of iron pipe being attached to the end of each line.
    The actual burner is a perforated block of stone of a conical form about 1 foot high; the gas is introduced by a lateral pipe at the bottom, and mixing with air is burned at the top of the block over which the pan is placed.

The whole arrangement is very primitive and imperfect, nothing of the nature of a stop valve being displayed anywhere on the line of pipes.  When the workman wishes to extinguish the flames, he places a brick on the top of the burner; but the gas continues to flow without interruption, and disperses in the atmosphere.  As, however, the work is done under open sheds, there is not much danger of explosions; but the smell of the gas is very prejudicial to the health of the workmen.

The saltpans are presently built by the proprietors of the gas wells, who leases them to salt makers at a rental of about Y(L?) 32 per annum.  The yield to the proprietors is therefore large, but the duration of the gas is very uncertain.