Gas-oil Ratio as Related to the Decline of Oil Production, with Notes on the Effect of Controlled Pressure

Abstract

Gas-oil ratios in the production of oil have recently attracted theattention of production engineers throughout the country and much work has beendone in an effort to reduce the volume of gas produced with each barrel of oil, thereby increasing the ultimate oil production. When occasion arises to use therelationship of rate of oil production and rate of casinghead gas production ithas ordinarily been assumed to be within reasonably narrow limits constantthroughout the life of the property after flush production is past. Inoperating a lease for conservation of gas or more efficient methods of recoverythe rate at which the volume of casinghead gas is declining is as essential asthe rate of decline of oil production. Much work has been done on the rate ofdecline of oil production and while our knowledge of the subject is far fromcomplete it is much greater than our knowledge of the rate of decline of thecasinghead gas. The data presented show that a definite relationship existsbetween the rate of decline of oil production and volume of casinghead gas, andthat a study of this relationship will usually indicate the effect on thegas-oil ratio which may be expected when controlled pressure is applied. Comparison of two curves with different rates of decline is difficult unlessone is expressed in terms of the other. Therefore in the discussion whichfollows the relationship of the rate of decline of casinghead gas to oilproduction is expressed by the cubic feet of gas produced with each barrel ofoil, or gas-oil ratio. The subject of this paper might more appropriately be "The oil-gas ratioas related to the decline of casinghead gas." Where gas is the principalexpelling force of the oil from the sand, the oil is produced with thecasinghead gas rather than the casinghead gas being produced with the oil.Since oil production figures are more familiar and it is easier to follow fromthe known to the unknown, the more common usage is continued by expressing thecasinghead gas in terms of oil production, but it must be kept in mind that thereverse is the more exact condition.