Laboratory Study of Water Coning In a Layered Model

Abstract

Abstract Experimental and numerical studies were made of water coning under twophase, immiscible. incompressible flow. A pie-shaped cylindrical sand pack having radial symmetry was the model. Saturations were measured in situ by 70 micro-resistivity probes embedded in the sand pack. Two models have been used; a homogeneous one and one which contained two horizontal, low-permeability layers, giving a 50: 1 permeability ratio with the bulk of the matrix. In the layered system studied, it was found that at the same pore volume of injection oil recovery decreased for higher oil viscosity or higher production rate. Stratification aggravated coning. A 10%-pore-volume bank of polymer solution injected at the oil-water contact delayed water breakthrough, but caused the drive water to viscous finger. Introduction Previous papers (1,2) have described results of numerical coning studies, a literature review on coning, and the effect f various parameters on the formation and behaviour of the water cone. The results indicated that the numerical model adequately simulated the experiment. The present paper deals with experimental and numerical studies which were carried out in a layered coning model. Four experiments were conducted: three of the experiments dealt with the effect of oil viscosity and production rate on the behaviour of the cone; a fourth involved the injection of a 10%-pore-volume polymer slug at the oil-water contact before water injection. Experimental Model For the experimental study, a pie-shaped, cylindrical coning model was constructed of Delrin plastic. The model was 40 cm high and had a radius of 50cm and an angle of 30 degrees. It was constructed of 5-cm-thick Delrin and was supported by a metal frame all around to avoid bulging during flow. To distribute the injected water uniformly across the bottom face of the sand pack; the bottom plate had fluid grooves that were overlain by several layers of 325-mesh monel screen. Seventy micro-resistivity probes were constructed and positioned inside the model for measuring the electrical resistivity. The resistivity probes were 316 SS wires and no screens were used at the measurement points. In this way, corrosion was eliminated and distortion of fluid flow was minimized. A thin, insulated wire led from each screen through a hole drilled in the side plates of the model to an electrical 70-poim junction box, and from there to a specially constructed 70-channel scanner. The scanner could scan any or all of the resistivity probes at a rate ranging from 1/2 to 60 seconds per probe. A timer permitted continuous scanning or time-lapse scanning ranging from once per hour to once every 8 hours. The output of the scanner was put through a digital voltmeter to a digital recorder. During a flow experiment, the resistivity at each probe thus could be measured and recorded automatically. The resistivity probes were positioned on a central symmetry plane, thus permitting measurements far from the boundaries of the model. Coordinates or probes in the z direction (measured positive downward) were 5.0, 10.0, 15.0, 20.0, 25.0, 30.0 and 35.0 cm.