Method of Anisotropy Modeling and its Application to Hydrodynamic Simulation

Abstract

In the practice of hydrodynamic modeling the anisotropy parameter (the ratio of vertical permeability to horizontal – kv/kh) is usually determined by experts as a fixed value varying in the range of 0.1-0.01, for the formation or for the field as a whole, and it is specified in the adaptation process of the model to the development history. This approach is applicable and is successfully used for deposits characterized by low degree of lateral heterogeneity. However, at the present time, a significant number of deposits are in development, the productive layers of which were formed in continental and coastal-marine environment, and therefore are distinguished by a complex geological structure due to high lateral and vertical anisotropy. For such objects the use of the conventional approach with a fixed value of kv/kh leads to an incorrect consideration of the influence of the heterogeneity on effective vertical permeability. Thus, the necessity of an alternative method for constructing the kv/kh cube, recommended for use in the complex structure of reservoirs, is obvious. The paper proposes a method for calculation the anisotropy parameter in 3D model cells intersected by wells as the multiplication result of the true anisotropy coefficient by the coefficient of pseudoanisotropy, which is modeled in the interwell space differentially for the facies zones by the method of cosimulation with NTG, reproducing the heterogeneity of the formation structure. The coefficient of true anisotropy is defined as the arithmetic average value from the results of core studies. The pseudoanisotropy coefficient characterizes the vertical heterogeneity of the formation within a single cell of a 3D grid. It is calculated for cells intersected by wells as a ratio of vertical permeability, which is the result of the geometric averaging of well log interpretation values, to lateral permeability, determined as the result of the arithmetic averaging [1]. For other cells of the 3D grid the anisotropy parameter is modeled by the method of cosimulation with NTG, which correlates with pseudoanisotropy coefficient. The use of the proposed method for modeling of anisotropy cube in process of hydrodynamic calculations allows to take into account the influence of heterogeneity on the effective vertical permeability differentially for facies zones and sedimentological units within facies zones.

Factoring Permeability Anisotropy in Complex Carbonate Reservoirs in Selecting an Optimum Field Development Strategy

“…Some studies [34][35][36] determine permeability anisotropy by core data. Techniques and approaches to factor in permeability anisotropy in reservoir simulation modeling are described in the works [37][38][39].…”