Recent Development and Use of Bottom-hole Choking

Abstract

Although the opinion has prevailed for several years that bottomhole chokingunder certain flow conditions should effect an increase in flow efficiencies, the use of bottom-hole chokes until recently has been limited in applicationmainly because of mechanical difficulties encountered in their construction. Within the past year, however, bottom-hole choking, through the development ofa removable type of choke, has been applied successfully under variousconditions of flow in many Mid-Continent fields. The observation of these fieldtests indicates that bottomhole choking, although not applicable to all flowconditions, has an important place in the operation of oil and gas wells. This paper gives briefly the conclusions drawn from the data obtained from theexperiments with this bottom-hole choke under various flow conditions, and adescription of the choke and its operation. Purpose of Bottom-hole Choking Since, in a normal well, the velocity with which the column of gas is movinggenerally has a direct bearing upon the quantity of oil it can lift, probablythe main purpose of bottom-hole choking is to accomplish an increase in thevelocity of this rising column, particularly in the lower portion of the tubingstring. This it does first, by expansion of the free gas accompanying the oil;next, by liberation and expansion of some of the occluded gas normally carriedin the oil to the surface; and lastly, by atomization, which results in a moreintimate and uniform mixture of the oil and gas. It is apparent, then, that ifthis velocity, particularly in the lower portion of the flow string, at a givenrate of production, is inefficiently low, owing either to an insufficientsupply of gas or to excessive surface choking, and slippage takes place, bottom-hole choking should bring about an increased velocity of the gas andhence an increased lifting capacity. But if the velocity of the column of gasat this same rate of production through a surface choke alone is at or above avelocity necessary to lift the oil efficiently, increasing the velocity bybottom-hole choking would probably serve no useful purpose, other than tosteady the flow by the better mixture of oil and gas and to lower deliverypressures.