An Experimental Investigation of the Effect of Fracture Dip Angle on Oil Recovery and Drainage Rate in Free Fall Gravity Drainage in Fractured Reservoirs Using a Glass Micromodel (A Pore Level Investigation)

Abstract

Gravity drainage is the main production mechanism in the gas invaded zone in naturally fractured reservoirs. However, there are large ambiguities and complexities, resulting from the dynamic of oil depletion from matrix blocks toward the fracture network. Visualization of drained oil at pore scale using glass micromodels provides the opportunity to better understand the effects of different parameters which might affect oil recovery from fractured reservoirs. In this work a micromodel apparatus generated by laser etching is used to perform some gravity drainage tests on the network patterns. The experiments were performed on double block systems using crude oil. The block to block interactions and the formation and changes of capillary bridges between matrix blocks were visually investigated. A suitable empirical model of gravity drainage is used for the prediction and evaluation of experimental data. The empirical model will be used for sensitivity analysis of fracture dip angle which might affect oil recovery efficiency and oil drainage rate, and as seen in experiments this parameter has a direct relationship to and positive effect on oil recovery. We also found the important rule of the block to block effect on the recovery of blocks and the higher recovery of upper matrix blocks than lower ones shows this reality; also it was claimed that the threshold height of fractured reservoir blocks doesn't show the true matrix capillary pressure of matrices, because of the block to block effect that helps the gravity forces in the matrix draining procedure. By increasing the block tilting angle up to α = 90 – tan – 1(y/x) as y and x are the 2-dimensional block sides lengths, the recovery of the block will increase but its initial drainage rate will decrease. It's a result of an increase in effective block height and increasing the capillary bridges stability which increases recovery, and the decrease of rate is due to capillary bridges frequency decreasing, which decreases the area open to flow.