MATHEMATICAL SIMULATION OF LIQUID-GAS MIXTURE SEPARATION IN A WELL AFTER FORMATION FLUID FLOW SHUT-OFF

Abstract

Shut-off of fluid recovery from one of formations at simultaneous selective-zone well operation leads to a natural process of liquid-gas mixture separation. Water holdup in a well after complete separation makes possible to estimate water cut of the blocked formation. This method has advantages over other techniques because provides acquisition of data on water cut for each formation individually, it is characterized by short-term effect because of fast liquid-gas mixture separation and by accuracy due to performance of measurements in close proximity to a formation. For this reason simulation of separation process in an interval from a suction pipe to borehole bottom becomes actual. After fluid movement stop in “pump suction” interval one can consider process of coarser-grained oil-in-water emulsion separation. It follows that time of complete separation depends on disperse phase size (oil droplets or gas bubbles) and difference in water and oil density. That is why movement of oil and gas bubbles in relation to a fixed water column according to Stokes' law is used as a movement model when simulating. From simulation results the following characteristics of phase distribution in a borehole are determined by means of application program package “Matlab” (density, pressure, phase concentration in mixture). These characteristics show the following: methods sensitive to changes in medium density are the most suitable for determination of phases interface limits; in case of use of geophysical sensors for definition of phases interface limits with help of a model it is possible to calculate a required quantity of these sensors for estimation of water cut with prescribed accuracy the model provides solution for various inverse problems connected with mixture separation in a well.