The Creek of Stinking Water
The name "Yenangyaung" literally means "creek of stinking water," a direct reference to the crude oil that has naturally seeped to the surface here for centuries. This area sits on the Yenangyaung anticline, an elongated, dome-like fold in the earth's crust. This geological structure traps petroleum. Porous sandstones of the Pegu and Eocene rock series, saturated with oil, are folded upwards and capped by impermeable layers of clay and shale, preventing the hydrocarbons from escaping. Over millennia, however, small faults and fissures have allowed some of this oil to migrate to the surface, creating the seeps that gave the area its name and its industry.
In 1855, geologist Thomas Oldham of the Indian Geological Survey was the first to scientifically connect the local practice of digging for oil only on the crest of the hill with the underlying anticlinal structure. This was one of the earliest recognitions of anticlinal theory in petroleum geology. The fold itself is asymmetrical, with the rock layers on the eastern flank dipping at angles up to 40 degrees, while the western flank is steeper, with dips reaching 50 degrees. This entire formation is part of the Salin Sub-basin, a forearc basin that began forming around 40 million years ago, situated between the Rakhine Yoma mountains to the west and a volcanic line to the east.
From Hand-Dug Pits to Industrial Derricks
Long before modern drilling, Yenangyaung was the center of a sophisticated indigenous oil industry. The rights to the oil fields were hereditarily controlled by 24 families, whose heads were known as twinzayo. These families oversaw the digging of wells entirely by hand. Teams of workers would excavate shafts, some reaching depths of 200 to 400 feet, a process that could take up to two years for a single well. In 1796, a British visitor, Captain Hiram Cox, recorded 520 such wells in operation. The unrefined "earth-oil" was used extensively as a preservative for timber, for caulking boats, and as a smoky illuminant in lamps.
The arrival of the British and the Burmah Oil Company in the late 19th century transformed the area. The company drilled its first mechanically-bored well in 1887, using cable-tool rigs. This new technology allowed for much deeper and more numerous wells. By 1911, more advanced rotary drilling tools were introduced, and eventually over 4,000 wells were drilled into the anticline. Production surged, reaching a peak of 15,953 barrels per day in 1918. The hand-dug wells of the twinzayo could not compete, and the traditional methods gradually faded as the Yenangyaung field became one of the British Empire's important petroleum assets.