A Neutron Method for Measuring Saturations in Laboratory Flow Experiments

Abstract

Abstract A method of measuring oil saturations in cores or sand packs by neutronscattering is described. This method permits local saturations to be measuredin a core enclosed in a steel pressure vessel without interrupting the flow.Calibration data and a saturation distribution measurement obtained with theapparatus are included by way of illustration. Introduction In laboratory flow experiments designed to study the mechanism of oilproduction it is frequently necessary to measure the oil saturation in a coreor sand pack containing oil, gas, and perhaps brine. It is sometimes desirablethat the saturation measurement refer to a relatively small portion of thecore, so as to eliminate end effects; that it be made without interrupting theflow, and that it be applicable to a core enclosed in a steel pressure vesselcapable of withstanding the pressures encountered in petroleum reservoirs. Noneof the usual methods of measuring saturation meets all of these requirements.To measure the gas saturation by observing the apparent compressibility of thegaseous phase would require the interruption of the flow and would give anaverage saturation for the. whole core. An electrical conductivity method isavailable for measuring brine saturations, but it is not applicable to oil. Aradioactive tracer might be used if a suitable substance could be found thatwould dissolve in the oil, emit gamma radiation, and not be adsorbed on thesand, the steel core holder, or in an aqueous phase. The large gamma-raybackground from the mass of radioactive oil in other parts of the apparatusmight, however, be undesirable. There remain for the saturation measurement methods involving the absorption orscattering of some penetrating radiation produced outside the apparatus. Itmight be possible to use X-rays or gamma rays; but these radiations would be somuch less strongly absorbed and scattered by the oil than by the steel walls ofthe core holder and by the sand that it seems doubtful that much precisioncould be attained. In a beam of neutrons, however, there is a radiation that isvery penetrating and, moreover, its scattering by substances containinghydrogen, such as oil, is qualitatively different from that occasioned by othermaterials. It would seem possible, and has proved to be quite practicable, tomeasure oil saturations accurately under the required conditions by means ofneutron scattering. The first, to our knowledge, to suggest neutron scatteringas a means of measuring oil saturation were F. Brons and J. A. Bottema, of theAmsterdam laboratories of the Bataafache Petroleum Maatschappij, who made a fewpreliminary experiments to test the method while they were engaged in exploringthe possibilities of neutrons for well-logging purposes. T.P. 1986