Procedures to calculate the viscosities of in situ reservoir gases and liquids from their composition have been developed and evaluated. Given a composition expressed in methane through heptanes-plus, hydrogen sulfide, nitrogen and carbon dioxide together with the molecular weight and specific gravity of the heptanes-plus fraction, the procedures are capable of calculating the viscosity of the gas or liquid at the desired temperature and pressure. The procedure for reservoir liquids was developed using the residual viscosity concept and the theory of corresponding states, and was evaluated by comparing experimental and calculated results for 260 different reservoir oils ranging from black to highly volatile. The average absolute deviation was 16 per cent. This is the first known procedure for calculating the viscosity of reservoir liquids from their compositions as normally available, i.e., including the heptanes-plus fraction. The procedure for reservoir gases uses a sequence of previously published correlations. Evaluation of the procedure was accomplished by comparison of 300 calculated and experimental viscosities for high-pressure gas mixtures in the literature. The average absolute deviation was 4 per cent. The calculations are useful fordetermining viscosities in compositional material balance computations andpredicting the viscosity decrease which occurs when gases, LPG, or carbon dioxide dissolve in reservoir oils. INTRODUCTION Methods to predict viscosities of reservoir fluids from the normally available field-measured variables have been presented. Beal,1 Standing,2 and Chew and Connally3 correlated oil viscosities with temperature, pressure, oil gravity and gas-oil ratio. Carr, Kobayashi, and Burrows4 and Katz et al.5 have presented correlations for reservoir gas viscosities as a function of temperature, pressure and gas gravity. Like all intensive physical properties, viscosity is completely described by the following function:Equation 1 where xi=1. Eq. 1 simply states that viscosity is a function of pressure, temperature and composition. These previous correlations1–5 may be viewed as modifications of Eq. 1, wherein one assumes more simple functions may be used. The assumptions are practical, because the composition is frequently not known. Further, the assumptions are sufficiently valid so that these correlations are frequently used for reservoir engineering computations. In compositional material balance6–9 computations, the compositions of the reservoir gases and oils are known. The calculation of the viscosities of these fluids using this composition information is required for a true and complete compositional material balance. For reservoir gases, Carr, Kobayashi and Burrows4 have presented a suitable compositional correlation. For reservoir oils, no correlation is available, and data from reservoir fluid analyses have been used7–9 for compositional material balance calculations.* From a theoretical point of view, this is entirely invalid. The reservoir fluid analysis, whether flash, differential, or other process, does not duplicate the compositions which occur during the actual reservoir depletion process, therefore the viscosities measured during reservoir fluid analysis are not those which occur in the reservoir. From a practical point of view, the "error" of using viscosities from reservoir fluid analysis is of varying and unknown significance. One can say qualitatively that the error is greatest where compositional effects are greatest, i.e., for volatile oil and gas condensate reservoirs and pressure maintenance operations. The first requirement to obtain a quantitative estimate of the significance of the error is to develop a reliable compositional correlation for the viscosities of reservoir oils. No such correlation has been available. Consistent with this requirement, the objective of this study was to develop a procedure to predict the viscosity of reservoir fluids from their compositions. Normally, the compositions of reservoir fluids are available expressed as mole fractions of hydrogen sulfide, nitrogen, carbon dioxide and the hydrocarbons methane through the heptane-plus fraction, with the average molecular weight and specific gravity of the latter. The final correlation was to use the composition in this form. While the more challenging objective of the study was the development of a correlation for the viscosities of reservoir oils, the viscosities of reservoir gases were also studied.

The results of this investigation showed that the practical design of falling cyclinder viscometers is possible.

The importance of accurate viscosity data to the chemical engineer cannot be overemphasized. A knowledge of viscosity and its variation with temperature and pressure is required for the solution of many of the problems that confront him, for example heat transfer, mass transfer, and fluid flow. A study of the literature on viscosity will show that no systematic approach has been formulated for the collection of these data.One reason for this lack appears to be caused by the limitations of the instruments used to measure viscosity. Instruments which give good results for gas viscosity, for example the Rankine viscometer, are often unsuited for liquid-viscosity measurement. Instruments which employ mercury drives are restricted to temperatures above the freezing point of mercury. The rolling ball viscometer is severely handicapped in regions where turbulent flow exists.The problem of evaluating and correlating gas and liquid viscosities of a single substance over the range of temperature and pressure of interest is compounded when the data are not internally consistent. Thus it would be desirable to obtain all the pertinent data with one viscometer.In the present research the materials investigated were methane, ethane, propane, and n-butane, and the fallingcylinder viscometer apparatus was developed to meet the needs of this re- 2. It can be used at extremes of temperature and pressure.3. The motion of the cylinder can be controlled to eliminate the undesirable components, for example spin and fishtailing.

No abstract

Statistical analysis of bids for federal offshore leases shows that the relative magnitude of the high bid and the amount of "money left on the table" each varies with number of bids in a way that is predictable. Joint bidders tend to bid on more sought-after leases and tend to bid higher than their solo-bidding competitors. Introduction Offshore bidding is big business. Since the first sale was held on Oct. 13, 1954, the total of bonuses paid to the federal government through 1974 exceeds $14 billion. This huge amount of money was spent as the result of bids prepared and submitted by the managements of prepared and submitted by the managements of companies desiring to produce oil and gas from the tracts offered for lease. The submitter of the competitively highest bid received the lease and the opportunity to find and produce oil and gas therefrom. Both the management and those who prepare bids for companies and the federal government as "owner" of the leases have a cogent interest in bidding behavior, each from their point of view. Further, the public also has a real interest because a substantial part of the oil and gas used by the public is derived from the leases - and the $14 billion spent for the leases. The fact that bids for an individual offshore lease are distributed lognormally has been observed many times. In light of the great uncertainty in estimating physical parameters from exploratory measurements and physical parameters from exploratory measurements and of the multiplicative process used to decide upon bids, the observed distribution of bids is to be expected based on the central-limit theorem. Furthermore, previous analyses have indicated that the observed bid distribution is consistent with the hypothesis that, in any given sale, all bids are drawn from a lognormal distribution with the same standard deviation. We accepted these results as a starting point for our analyses; the consistency of our results confirms the adequacy of these statistical postulates. In our analyses we considered all leases issued to competitive bonus bids through 1974. Our analyses consisted of four major parts:We first determined the standard deviation of the logarithms of bids for all sales. We found that by deleting abnormally low bids we obtained a consistent pattern of results and that no significant time trend in the standard deviation of bids by sale was indicated.We analyzed the manner in which the high bid relative to the mean bid on a tract varied with number of bidders, nl. We concluded that observed behavior is consistent with the hypothesis that the high bid is the largest value of a random sample of size nl drawn from a population whose mean is that for the lease and whose population whose mean is that for the lease and whose variance is that for the sale.We analyzed the way in which "money left on the table" varies with number of bidders, nl. We concluded that observed behavior is consistent with the hypothesis that the highest and second highest bids are the largest and second largest values of a random sample of size nl drawn from the bid population.We compared solo bids with joint bids and concluded that joint bidders tend to bid on more sought-after (and, apparently, more valuable) leases and that they tend to bid higher, on the average, than their solo-bidding competitors. Standard Deviation of Bids by Sale Our examination of historical bids revealed that inordinately low bids have been submitted occasionally, possibly with less than normal technical evaluation. possibly with less than normal technical evaluation. JPT