Effect of Heterogeneity on the Performance of Immiscible Displacement with Horizontal Wells
Authors: Gharbi R.B. , Peters E.J. , Afzal N. 
Published: December 2007

A three-dimensional, finite difference, chemical flood simulator (UTCHEM) was used to study the performance of immiscible displacement with horizontal and vertical wells in several heterogeneous reservoirs. Three-dimensional heterogeneous permeability fields were generated geostatistically with Dykstra-Parsons coefficient and spatial correlation as characterizing parameters. A total of twenty-one permeability fields were generated to cover a wide range of Dykstra-Parsons coefficients and spatial correlations. Initially, simulations of immiscible displacement with two horizontal wells (one injector and one producer) were performed in all these permeable media. The effect of the amount of cross flow between producing layers on the flood performance was investigated. These results were then compared to those obtained with two vertical wells (one injector and one producer) for all the permeable media. Finally, investigations were carried out on a highly heterogeneous to study in detail the sensitivity of the displacement performance to the horizontal well length and to the ratio of horizontal to vertical permeability using various well combinations. These well combinations consisted of vertical injector-vertical producer, horizontal injector-horizontal producer, vertical injector-horizontal producer, and vertical producer-horizontal injector.

Results show that the degree and the structure of the heterogeneity of the reservoir have a significant effect on the efficiency of immiscible displacements with horizontal wells. Long horizontal wells in highly heterogeneous reservoirs do not necessarily guarantee improved oil recovery.

Introduction

A worldwide interest exists today in using horizontal wells in oil recovery operations. An extensive list of references exists on horizontal wells and their applications. Horizontal wells are common in primary oil recovery methods in which oil is produced by natural drive mechanisms, and also in secondary or tertiary oil recovery methods, in which oil is produced by fluid injection. Horizontal wells have been used in water flood applications in miscible flood applications, and also in thermal oil recovery applications. The primary reason for this interest in horizontal wells is that a horizontal well provides a large contact area with the reservoir, and therefore enhances the well productivity and efficiency or the well injectivity if used as an injection well. In addition, the technology for drilling horizontal wells has improved substantially, thus reducing their drilling and completion costs.

Horizontal wells can be the solution to reservoirs with low productivity. Sheikholeslami et al. found that reservoirs containing vertical fractures and/or large voids are good candidates for horizontal well applications. In these cases, there is a good probability that the horizontal wellbore productivity is enhanced by the resulting high vertical permeability. Murphy concluded that water and gas coning could be reduced by the use of horizontal wells because of the reduction in the near wellbore fluid velocities for the same amount of produced fluid. All these reasons have made the application. of horizontal wells in oil recovery operations an economically viable option.

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