Application of Laboratory PVT Data to Reservoir Engineering Problems

Abstract

The paper summarizes the historical background of thepressure-volume-temperature analyses of reservoir fluids, the errors involvedin both the sampling and testing of reservoir fluids, the type of informationrequired of a PVT determination, and the field conditions that limit theapplication of anyone analysis. Particular emphasis is placed on the necessityfor approximating as closely as possible the liberation sequence occurring inthe producing formation, flow string, and surface separators. A combineddifferential and flash or "composite" liberation is suggested as thebest means of approximating this liberation sequence. Historical Background Petroleum reservoir engineering commonly is considered to be one of thenewest fields of petroleum science, yet much work of a theoretical andintuitive nature was done many years before the modern techniques of reservoiranalyses were developed. The period 1910–1924 saw considerable work in the field of reservoirbehavior done by the U. S. Bureau of Mines. This work, although entirelytheoretical, pointed out the importance of gas in the recovery of oil from thereservoir. The statement by J. O. Lewis that 20 per cent or less of theoil originally in place in a pool was recovered from the ground under uncurtailedproduction conditions caused some operators to re-examine and modify theirproduction methods. However, though these works showed methods of productionthat have subsequently resulted in greater oil recoveries, they in general wentunnoticed, even though there was a fear that the nation's petroleum resourceswere being exhausted. The period 1924–1933 saw the industry take considerably more interest inreservoir behavior because of an unfounded fear of its inability to replace oilreserves, the possibility of government regulation, and the energy of one man, Henry L. Doherty. Doherty aroused heated discussions in the industry concerningconservation. To prove or disprove his theories the first experimental work onthe reservoir behavior of petroleum was undertaken. The papers of Dow andCalkin, Beecher and Parkhurst, and Mills and Heithecker are classics althoughtheir experimental procedures were crude. These papers proved that theproperties of petroleum in the reservoir are quite dissimilar to the propertiesmeasured at the well head. Gas dissolved in the oil phase was recognized ashaving considerable importance as had been predicted by the earliertheorists. T.P. 3710

Evaluating Constant-Volume Depletion Data

“…It is good practice to ask if a laboratory reports measured or smoothed data, and to what extent material-balance-derived data are used in final CVD reports.) (2) where nL is moles of liquid with composition Xj' nv is moles of vapor with composition Yj, and n t is total moles in the system with composition Zj, each associated with pressure stage k. Subscript} designates components methane, ethane, etc. Eq.…”

“…Dodson et al 2 suggested an experimental procedure for determining so-called black-oil PVT properties used in two-phase flow equations and solution-gas drive material-balance relations. Current laboratory procedures for estimating oil formation volume factor, Bo, and solution GOR, Rso, only approximate the Dodson et al method without flashing the liquid phase at each stage of the differential vaporization process.…”

“…Many other adjustments of the C 7 + characterization procedure were tried. None of these were particularly helpful, though some are worth mentioning: (1) extending the C 7 + split to C 40 + such that the last component was very heavy, (2) increasing the number of MCN groups used to nine, C25 + inclusive, (3) splitting the '" 10' '" 0. JOURNAL OF PETROLEUM TECHNOLOGY C 7 + fraction into eight SCN groups and a C 15 + fraction, and (4) using TBP Kuop factors instead of those estimated from Eq.…”

“…The method was first suggested by Dodson et al 2 in 1953 for solution-gas/ crude-oil systems. Their method, however, requires expensive and time-consuming liquid sample removals and experimental flash separations.…”

Integrated Analysis of Optimizing Tubing Material Selection for Gas Wells

“…In order to estimate and analyze the reservoir fluid behavior, the PVT report (components measurement only) was used to calculate fluid saturation pressure and relative volume using the equation of state method [15]. Peng-Robinson, Zhou, et al, and the Standing-Katz correlation were used to estimate phase envelope, gas viscosity, and oil density respectively.…”