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Collaborating Authors
Results
The viscosity of the oil in the reservoir is one of the properties thatinfluence its movement through the sand to producing wells. Measurements ofviscosity, therefore, are pertinent to problems associated with well behaviorand with the estimation of recoveries, and afford an indirect means for partialevaluation of various methods of controlling reservoir behavior. The effect ofdissolved gases on the viscosity of crude oil has been determined, but no datahave been published on the viscosity of representative samples of reservoiroils, This paper describes a simple instrument that has been used to determinethe viscosities of a number of subsurface oil samples at the temperatures andpressures existing in the reservoirs, and presents the results of thedeterminations for typical fields. Construction of the Apparatus The principal requirements of any instrument used for the examination ofsubsurface samples are that it be strong and simple both in design and inmethod of operation. Accuracy beyond that of the degree of reproducibility ofsubsurface samples from various wells in a reservoir or exceeding that of thecommon measurements of reservoir temperatures and pressures is not required.Because of the expense of procuring subsurface samples, it is necessary alsothat the instrument operate on a relatively small fraction of a sample, leavingthe remainder for other tests, and that there be few or no failures of the equipment to cause undue delay orloss of a sample. After preliminary experiments with a falling bullet, the results of which werenot satisfactory, a simple viscosimeter was built of the rolling ball typefirst proposed by Flowers and later used by several investigators. Theapparatus consists essentially of a removable, accurately bored cylindricalbarrel of 1/4-in. nominal internal diameter, 8 in. long, in which a closely fitting steel ball rolls through the oil with thebarrel inclined at a definite angle, The ball makes contact at one end of thebarrel with an insulated electrode, closing an electrical circuit, whichactuates a buzzer. The measurements consist essentially in determining the timerequired for the ball to travel the length of the barrel. The details of the construction are shown in Fig. 1. The barrel in which theball rolls was made from a section of 2s-caliber blank rifle barrel, speciallybored to an exact uniform diameter and polished. The barrel slides snugly intoa hole bored in a solid stainless-steel cylinder, an upper external shoulder ofthe barrel compressing a small spring, and is held in place by a hollow nut.The spring prevents the barrel from seating against the bottom of the boredhole in the cylinder, while narrow external longitudinal slots in the barrelpermit fluid to flow around it and through the bottom. T.P. 1220
Deep drilling has led to the development of numerous pools which yieldproducts consisting predominantly of natural gas accompanied by high-gravitywater-white or slightly straw-colored liquid. Yields of this"condensate" or "distillate," as it is commonly called, vary fromtraces to over a hundred barrels per million cubic feet of gas. The fact thatthis liquid exists in the reservoir as an integral part of the gas phase and isformed by condensation attending simultaneous reduction of pressure andtemperature after its entry into the well was apparently first recognized about1932.1 The nature of the physical phenomena involved in this condensation wasclarified for the petroleum industry in 1933 by a report by Sage, Schaafsma, and Lacey of the results of an experimental investigation of the behavior ofmixtures of methane and propane. Search of the literature has revealed that the condensation of liquid fromgaseous mixtures by isothermal pressure reduction is not a new discovery.Kuenen was led by theoretical considerations to expect such a phenomenon, andin 1892 reported the results of experimental verification of his deductions.This was followed by a considerable amount of work on the phase relations ofmixtures by Kuenen and by others, mostly in European universities. Since 1930investigators in this country have reported experimental data on the properties and behavior of a number of hydrocarbon systems. It is now generally known that in the presence of natural gas the solubility inthe gas phase of the heavier and normally liquid hydrocarbons increasesrapidly with increasing pressure above 500 to 1000 lb. per sq. in. Thus, at pressuresof 2500 lb. per sq. in. or higher a gas may contain appreciable quantities ofhydrocarbons with normal boiling points as high as 600?F., which in turn may becondensed from the gas phase by the reduction of their solubility thereinattending pressure reduction. The combined effects of pressure and temperatureon condensation and vaporization of mixtures are most readily visualized by thestudy of phase diagrams. Since the construction, application, andinterpretation of such diagrams have been described fully in readily availableliterature, this paper will not review the theoretical aspects of thissubject. While the behavior of gas-distillate systems is now clearly understood, atleast in a qualitative way, most of the published work deals with the resultsof laboratory studies of binary systems or of synthetic mixtures ofhydrocarbons, and although several systematic investigations of the effects ofseparator pressure and temperature on the yields of liquid product fromgas-distillate wells have been made it appears that in all cases thelimitations have precluded the construction of even approximately completephase diagrams for naturally occurring systems. T.P. 1269
- Reservoir Description and Dynamics > Fluid Characterization > Phase behavior and PVT measurements (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring (1.00)
- Facilities Design, Construction and Operation (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management (0.93)
The application of hydrocarbon equilibrium data to various problemsencountered in refining and in natural gasoline recovery is an old and wellestablished practice. Both generalized data and data on? specific hydrocarbonsystems have been made available by a number of investigators. More recentlysuch data have been applied to the relations governing the separation of oiland gas both in the reservoir and at the surface. Most of the applications toproduction problems, however,. have been based upon examinations of surfacesamples of oil and gas. This paper describes a technique that has been usedsatisfactorily in a number of cases to calculate directly from the hydrocarbonanalysis of and auxiliary laboratory data on a subsurface sample of thereservoir fluid the behavior of the oil and gas during the various stages ofseparation at the surface incident to production. Types of Information Calculated The system of calculations is not designed to supplant field data, but ratherto correlate with them laboratory data obtained under controlled conditions inorder to obtain a more complete and exact picture than usually is possiblethrough the use of field data alone. The chief advantage of the calculations isthe possibility of their use at a minimum of both time and expense to determinecompletely the effect of any possible operating technique upon each of thefollowing:The gas-oil ratio resulting from liberation of the dissolvedgas; the composition and gasoline content of the liberated gas; thecomposition and gravity of the residual oil; the amount and composition of the gas liberated upon flashing the oil from the separator to the stock tank; the shrinkage of the oil in passing from the reservoir to the stocktank. This information is frequently essential to the correct determination of theadvisability of installing a natural gasoline plant, to design such a plant totake care of seasonal production, and to determine the optimum separatorpressures to carry in various parts of a field. T.P. 872