Classification of Flowing Wells with Respect to Velocity

Abstract

The observations and data presented in this paper are the result ofextensive study of flowing wells, most of which were in the Maracaibo LakeBasin of Venezuela. The Lago Petroleum Corpn. had extensive production in thisarea, gas-oil ratios were low, and the problem was to determine whether bycareful handling of the wells with respect to flowing conditions and byconserving the gas, the oil production of the wells could be maintained bynatural flow until it had declined to a rate which could be handled with anordinary working barrel, thereby avoiding the high cost of gas-lift equipmentinstallation in the lake bed. The problem was complicated by the nature of thewells themselves. Production is from soft, comparatively unconsolidated sands, necessitating screen pipe in all wells. It was not only necessary to keep thewells flowing but to keep them flowing without heading, as the release ofpressure upon making a head brought large quantities of sand into the wells, sanding them up or possibly cutting out the screen pipe. In furtherance of theplan of keeping wells flowing as long as possible, each well was equipped witha casinghead and tubinghead recording pressure gage, and an oil and gasseparator set. About one-half of the wells were equipped with gas meters. Allwells were tubed before bringing into production. Frequently individual gageswere taken on each well. A large scale chart was plotted for each well, showingdaily oil production, gas production, gas-oil ratio, tubinghead pressure andcasinghead pressure. Any deviation from the normal was immediately checked andthe condition remedied if possible. Theory of Flowing Wells Based upon considerable study of these records, it is believed that the flow ofa well actuated by gas is mainly a problem in velocity, a certain minimumvelocity in the flow string being necessary for the gas to carry the oil. Ifthis minimum velocity is not obtained the oil drops back and the well heads orgoes dead. The point of minimum velocity is of course at the bottom of thetubing, where the gas is under the highest pressure and therefore occupies theleast volume.