A new wormhole mechanistic model for radial acid flow geometry using novel 3D flow correlations

Abstract

In carbonate reservoirs, matrix acidizing is used to improve well performance by creating conductive channels called wormholes. Predicting wormhole propagation rate in radial acid flow geometry up to the real wellbore scale is the main problem regarding designing field operations in previous studies which are still challenging. In this study, a new mechanistic approach is presented to predict the radial flow acidizing up to near wellbore scale by considering the vital effects of porous media size and geometrical parameters of wormhole patterns.Accordingly, wormhole tip velocity and wormhole wall fluid loss rate will be introduced as the scale transferring parameters between different porous media sizes which are correlated in terms of rock diameter and wellbore height, wormhole size and density. These novel correlations are extracted from the large databank of flux distribution between rock matrix and wormhole channel obtained in 60 different 3D FEM flow simulations for various patterns of wormhole propagating and different wellbore sizes. In addition, an HPHT radial acid flooding setup is designed and constructed to perform radial acid coreflood on ultra-low permeable rocks (k«1md) for model validation. During the experiments, the breakthrough pore volume, pressure behavior and CT scan of samples are closely monitored. The results showed that due to the tight window of pore size distribution, faster breakthroughs with 1.23 and 1.45 pore volumes occurred in these tight samples compared to those reported already which are confirmed by developed model prediction. Besides, the model results showed that increasing the rock height (open-hole interval) would increase wormhole tip velocity and decrease acid breakthrough time. In addition, the higher temperature shifted the acid response curve to the right, toward higher acid breakthrough volume and higher acid concentration shifted it toward lower breakthrough volumes. The model is validated using radial acid experiments and previous radial acid models for different rock sizes with good agreement (R2 = 0.9547, MSE = 0.02161 and RMSE = 0.14701). The new radial acidizing model is capable to quickly predict wormhole propagation rate up to wellbore scale without requiring excess up-scaling data due to considering wide ranges of porous rock sizes from (25.4–152.4 cm) diameter and (5–25.4 cm) pay zone height (sufficient size for considering repetitive wormhole patterns). This technique can be utilized for tuning parameters of various radial cases to predict the acid tests results leading to reduce the number of required experiments.