History of produced water

History

Early U.S. settlements commonly were located near salt lakes that supplied salt to the population. These salt springs were often contaminated with petroleum, and many of the early efforts to acquire salt by digging wells were rewarded by finding unwanted amounts of oil and gas associated with the saline waters. In the Appalachian Mountains, saline water springs commonly occur along the crests of anticlines.

In 1855, it was found that petroleum distillation produced light oil that was, as an illuminant, similar to coal oil and better than whale oil. This knowledge spurred the search for saline waters containing oil. With the methods of the salt producers, Colonel Edward Drake drilled a well on Oil Creek, near Titusville, Pennsylvania, in 1859. He struck oil at a depth of 70 ft, and this first oil well produced approximately 35 B/D.

Early oil producers did not realize the significance of the oil and saline waters occurring together. In fact, it was not until 1938 that the existence of interstitial water in oil reservoirs was generally recognized. Torrey was convinced by 1928 that dispersed interstitial water existed in oil reservoirs, but his colleagues rejected his belief because most of the producing wells did not produce any water on completion. Occurrences of mixtures of oil and gas with water were recognized by Griswold and Munn, but they believed that there was a definite separation of the oil and water, and that oil, gas, and water mixtures did not occur in the sand before a well tapped a reservoir.

It was not until 1928 that the first commercial laboratory for the analysis of rock cores was established, and the first core tested was from the Bradford third sand (Bradford field, McKean County, Pennsylvania). The percent saturation and percent porosity of this core were plotted vs. depth to construct a graphic representation of the oil and water saturation. The soluble mineral salts that were extracted from the core led Torrey to suspect that water was indigenous to the oil-productive sand.

Shortly thereafter, a test well was drilled near Custer City, Pennsylvania, that encountered greater than average oil saturation in the lower part of the Bradford sand. This high oil saturation resulted from the action of an unsuspected flood, the existence of which was not known when the location for the test well had been selected. The upper part of the sand was not cored. Toward the end of the cutting of the first core with a cable tool, core barrel oil began to come into the hole so fast that it was not necessary to add water for the cutting of the second section of the sand. Therefore, the lower 3 ft of the Bradford sand was cut with oil in a hole free from water. Two samples from this section were preserved in sealed containers for saturation tests, and both of them, when analyzed, had a water content of approximately 20% pore volume. This well made approximately 10 BOPD and no water after being stimulated with nitroglycerine. Thus, the evidence developed by the core analysis and the productivity test after completion provided a satisfactory indication of the existence of immobile water, indigenous to the Bradford-sand oil reservoir, which was held in its pore system and could not be produced by conventional pumping methods.

Fettke was the first to report the presence of water in oil-producing sand; however, he thought that the drilling process might have introduced it. Munn recognized that moving underground water might be the primary cause of migration and accumulation of oil and gas. However, this theory had little experimental data to back it until Mills conducted several laboratory experiments on the effect of moving water and gas on water/oil/sand and water/oil/gas/sand systems. Mills concluded that "the updip migration of oil and gas under the propulsive force of their buoyancy in water, as well as the migration of oil, either up or down dip, caused by hydraulic currents, are among the primary factors influencing both the accumulation and the recovery of oil and gas." This theory was seriously questioned and completely rejected by many of his contemporaries.

Rich assumed that "hydraulic currents, rather than buoyancy, are effective in causing accumulation of oil or its retention." He did not believe that the hydraulic accumulation and flushing of oil required rapid movement of water, but rather that oil was an integral constituent of the rock fluids, and that it could be carried along with them whether the movement was very slow or relatively rapid.

The effect of water displacing oil during production was not recognized in the early days of the petroleum industry in Pennsylvania. Laws were passed, however, to prevent operators from injecting water into the oil reservoir sands through unplugged wells. In spite of these laws, some operators at Bradford secretly opened the well casing opposite shallow groundwater sands to start a waterflood in the oil sands. Effects of artificial waterfloods were noted in the Bradford field in 1907 and became evident approximately 5 years later in the nearby oil fields of New York. Volumetric calculations of the oil-reservoir volume that were made for engineering studies of the waterflood operations proved that interstitial water was generally present in the oil sands. Garrison and Schilthuis reported on the distribution of oil and water in the pores of porous rocks. They described the relationship between water saturation and formation permeability, while discussing the origin and occurrence of "connate" water in porous rocks.

Lane and Gordon first used the word "connate" to mean interstitial water deposited with the sediments. The processes of rock compaction and mineral diagenesis result in the expulsion of large amounts of water from sediments and movement out of the deposit through the more permeable rocks; therefore, it is highly unlikely that the water now in any pore is the same as when the particles that surround it were deposited. White redefined connate water as "fossil" water because it has been out of contact with the atmosphere for an appreciable part of geologic time period. Thus, connate water is distinguished from "meteoric" water, which entered the rocks in geologically recent times, and from "juvenile" water, which came from deep in the earth’s crust and has never been in contact with the atmosphere.

Meanwhile, petroleum engineers and geologists had learned that waters associated with petroleum could be identified, with regard to the reservoir in which they occurred, by knowledge of their chemical characteristics. Commonly, the waters from different strata differ considerably in their major dissolved chemical constituents, making the identification of water sourced from a particular stratum possible. However, in some areas, the concentrations of dissolved constituents in waters from different strata do not differ significantly, and the identification of such waters is difficult or impossible. Corrosion and scale deposition due to produced water describes new techniques to assist in this process, because several new analytical and statistical techniques for trace species apply nicely to this problem.

The enormous quantities of water produced from many fields originally surprised operators and, even today, water-handling costs continue to be significant to company management trying to reduce costs. The amount of water produced with the oil usually increases as the amount of oil produced decreases, even during primary production. At the end of the life of some reservoirs, 100 times (or more) as much water is processed as oil sold.

The history of oil production is replete with operators who decided that the water-handling costs were too high for an older field to be profitable, so they sold the property to another operator. The new operator finds ways of reducing the impacts of that water to produce the smaller oil stream profitably, until they become discouraged and sell to yet another operator, and so on. Very few mature reservoirs, especially those that have undergone secondary and tertiary recovery, have been completely abandoned because new technology and better engineering have made it economical to produce oil at extremely high water cuts or to reduce the water cut by controlling water production in the reservoir and wells. It is the challenge of producers to recover the most oil from the reservoir profitably, which means discovering methods to minimize the impacts of produced water for that particular field.

Noteworthy papers in OnePetro

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See also

Produced oilfield water

PEH:Properties_of_Produced_Water

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