TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWhen oil is produced under high water-cut conditions, oil in water emulsions can be formed. The break-up of oil droplets predominantly takes place in the choke valve. We have conducted laboratory experiments to investigate the effect of flow through a choke valve on the oil-droplet-size distribution in the emulsion. In these experiments the choke is modeled as a circular orifice in a pipe. The droplet sizes after break-up can be correlated to the mean energy dissipation rate per unit mass in the orifice. The experiments have been conducted with two set-ups on a different scale. The relation, which we have derived for the maximum stable droplet diameter downstream of the orifice can be applied to both scales. Furthermore the effect of oil viscosity on the droplet sizes after break-up has been investigated.

Frequently oil is produced while, simultaneously, large amounts of water are produced as well. Under these circumstances it is important to have compact and efficient deoiling equipment at one's disposal. After some remarks on otherde-oiling methods, the attention in this paper is focused on three separationtechniques: plate separation, centrifugation and the use of hydrocyclones. The working principles are described and subsequently typical data on separation efficiency, geometry of the separator section, separator volume and critical oil-droplet diameter are derived or given. Analysis of these data shows, that the ranking with respect to performance of the three separator types is: centrifuge, hydrocyclone, plate separator. In the last section of the paper attention is given to some recent developments concerning centrifugation and the use of hydrocyclones. P. 391

Is paper WS selected for presentation by an SPE Program committee following review of information cnntained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been revtewed by the S@ety of Petroleum Englneera and are subject to mrretion by the author(s). The material, as presented, does not neceaearlly reflect anỹ ition of the society of Petroleum Engineers, ita ofricera, w members. Papers presented at SPE meetings are subject to pubK@tion retiew by Editorial Committees of the Scdety of Petroleum Englneara. Electronic reproduction, distribution, or storage of any part of this paper for mmmerdal pu~ee tithwt the written mnsent of the Sdety of Petroleum Engineers Is prohibited. Permission to raproduce In print is restricted to an absbad of not more than 300 wurds; illustrations may not be mpied.The abstrad must mntsln wnsplcuous atiowledgment of Mere and by whom the paper was preeented. Write Librartan, SPE, P.O. Mx 833636, Ritiardson, TX 7S0S3-3836, U.SA., fax 01 -972-952-%3S. AbstractFor oil production under high water cut conditions the efforts needed for de-oiling of the production water are mainly determined by the oil-droplet-size distribution of this water. This distribution is predominantly the result of droplet breakup in the choke valve. To determine the effect of the choke valve on the droplet-size distribution, we have conducted laboratory experiments in which we used a circular orifice in a circular pipe. With the help of theory on droplet break-up in turbulent flow and with knowledge of the flow field inside an orifice, a prediction of the distribution after break-up can be made. It is shown that the droplets increase in size with increasing oil viscosity and Mermore it appears that, for the description of the break-up process, the distribution of the turbulence over the orifice zone is an important factor.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper describes core-flow experiments with sandstone cores and artificial produced water. The water contained small quantities of solids in the form of ground sandstone, of oil in the form of droplets, or both solid particles and oil droplets. In the case of water with solid particles the parameters having the largest influence were particles concentration and, to a lesser extent, size. Usually a considerable decrease of the permeability of the first section of the core was observed after an amount of a few hundred pore volumes was injected. For a relatively low particle concentration, in combination with a relatively small average particle size, this decrease was less severe. Injection of water with only oil droplets eventually led to a small permeability decrease in all core sections. Also for injection of water containing both oil droplets and solid particles, the particles concentration appeared to be the most influential parameter. Here the presence of oil usually led to some additional permeability decrease.

In downhole dehydration the produced fluids - oil and water, with a low oil/water ratio - are separated at the bottom of the well by means of a hydrocyclone. In many cases this separation can be carried out successfully, because the size of the oil droplets is generally in such a range, that the hydrocyclone can remove the oil from the produced water. Potential problems are connected with the possible occurrence of very small oil droplets, because this may lead to the presence of some oil remaining in the produced water, which is unfavorable from an economical point of view and, moreover, which can lead to difficulties with subsurface injection of this water. Notably production from reservoirs with a relatively low permeability may lead to the presence of small oil droplets. For conventional high water-cut oil production, the presence of very small oil droplets is predominantly caused by droplet break-up in the choke valve. Further downstream these small droplets determine the complexity of the separation units. It is shown that the geometry of the choke valve influences the break-up process. Consequently, by modification of the geometry of this valve it must be possible to reduce the break-up. It is expected that in this way a substantial droplet size increase can be realized. Introduction As an oil field matures the water-cut increases, which gives risetoincreasedoperationalcostsand makes increasedseparation efforts necessary. To deal with these problems it is important to generate and develop new technical solutions. In this paper technical aspects of two alternative ways to deal with a high water-cut are treated, viz. downhole dehydration and reduction of oil droplet break-up. The idea of downhole dehydration is not new, but we look again at this technique, mainly with regard to separation aspects, and taking into account data from recent work on oil/water morphology by Janssen1. Break-up reduction concerns means to influence the average oil droplet size of the produced water in the production system (more specifically: in the choke valve), so that the oil-water separation equipment at surface can become somewhat less complicated. To the best of our knowledge this second option has not been considered up till now. We will treat the feasibility of this idea on the basis of work by Van der Zande2. Downhole Dehydration Production of oil making use of downhole dehydration has been treated by a number of authors, of which we mention Kjos et al.3, Verbeek et al.4, and Jacobs and Schmidt5. The idea is that, with respect to separation, the produced fluids are treated downhole and not at the surface. To this end a separation unit is positioned at the bottom of the well. The produced fluids are forced to enter this unit (emulsion pump), subsequently pass a separation device (hydrocyclone) and leave the unit as two streams, an oil-rich stream and a water-rich stream. The oil-rich stream is pumped to the surface (concentrate pump), while the water-rich stream is injected into a suitable formation. The two main objectives of downhole dehydration are to bring an oil-water mixture to the surface with a considerably higher oil concentration than in the absence of a downhole dehydration unit and, simultaneously, to prevent that the bulk of the produced water arrives at the surface. The higher oil concentration of the produced oil-water mixture will be advantageous, because oil droplet coalescence will be promoted. More important, however, is that a much lower capacity of the separation system at the surface is needed, as a result of the much lower amount of produced fluids.