Losses of Crude Oil in Steel and Earthen Storage

Abstract

The extent of losses, due to evaporation, sediment, and water, in crude oilstored in steel tanks, is a very interesting question, and particularly so atthis time, when every reasonable measure should be employed to eliminate allpossible losses of this important natural product. Available information onthis subject is incomplete; e.g., during the development of the Cushing Field, considerable surplus oil was stored in steel tanks, but from time to time, owing to changes in weather, some losses by evaporation and short storage roomon the leases, these tanks were topped out, thus rendering inaccurate anysystem designed to determine the average rate of evaporation or other losses ofthe oil over a given period. Furthermore, the losses, as shown by the recordsat the time, as a result of hasty gages, failed to take into account thetemperature and gravity of the oil. Losses may be classified roughly asoccurring from evaporation, presence of sediment and water, and leakage. Thecoefficient of expansion and contraction of crude oil, in relation totemperature conditions, is of material importance; also, the rate ofevaporation is dependent upon the gravity of the oil, as the escape of thelighter hydrocarbons in fresh Cushing oil, of from 40 to 42 gravity, on a warmday is considerable, and from available records of temporary storage, it issafe to assume that a loss of 1 to 1? per cent. in volume will easily occur inlight crude oil of Cushing grade over a period of 6 months, including thesummer season. The presence of sediment, water, and other impurities, in theoil will also cause more or less deterioration in quality, particularly whenthe fresh production is run direct from the gage tanks, or from the wells onthe lease to steel storage, as is often the case when an oil field is beingrapidly developed. The bad oil will settle to the bottom of the tanks and maybe determined by thiefing and running a centrifuge test on the sample. Theamount of water in the oil depends entirely on the conditions under which it isproduced. Sometimes in large producing wells, with heavy gas pressure, somewater may come in with the oil, particularly if the well has been drilled tothe top of a water sand. Under these conditions, cut oil is often produced, which, if not settled out, is carried over into the steel tanks. AIME 061–56