System and Method for Simulation of Gas Desorption in a Reservoir Using a Multi-Porosity Approach

Abstract

A hydrocarbon shale reservoir simulation system and method represented by a model having at least four different types of porosity nodes is described. The method includes the computer-implemented steps of characterizing porosity nodes within the model as one of natural fracture pore systems, matrix pore systems, induced fracture pore systems or vug pore systems. Following characterization, transfer terms between nodes are identified. Transfer terms may include transfer terms between vug nodes, matrix nodes, natural fracture nodes and induced fracture nodes. Once transfer terms have been assigned, the linear system for the model can be solved utilizing a linear solver. The method further includes the steps of utilizing the characterized pore nodes to define one or more subgrids that represent a zone within the reservoir, wherein the zone includes at least one node of each porosity type; and wherein the linear solver is applied by subgrid or associated sub-grids.

What is claimed is: 
     
         1 . A method for performing simulation of a shale reservoir represented by a model, the method comprising computer-implemented steps of:
 characterizing at least three different porosity types for the modeled reservoir, the at least three different porosity types selected from the group consisting of natural fracture pore systems, matrix pore systems, induced fracture pore systems and vug pore systems;   identifying transfer terms between the at least three porosity types; and   solving a linear system for the model using a linear solver.   
     
     
         2 . The method of  claim 1 , wherein the formation is characterized with at least one of each of the porosity types of natural fracture pore systems, matrix pore systems, induced fracture pore systems and vug pore systems. 
     
     
         3 . The method of  claim 1 , wherein the characterized pore types are utilized to create one or more subgrids that represent a zone within the reservoir. 
     
     
         4 . The method of  claim 3 , wherein each zone includes a plurality of nodes of at least one of the porosity types. 
     
     
         5 . The method of  claim 3 , wherein a subgrid for at least three different porosity types is created for a zone. 
     
     
         6 . The method of  claim 3 , wherein a subgrid for each of the four porosity types is created for a zone. 
     
     
         7 . The method of  claim 5 , wherein each zone includes a plurality of nodes of at least one of the porosity types. 
     
     
         8 . The method of  claim 7 , wherein transfer terms between the same node types within the same subgrid are identified. 
     
     
         9 . The method of  claim 7 , wherein transfer terms between different node types in different subgrids are identified. 
     
     
         10 . The method of  claim 7 , wherein transfer terms between the different node types within the same subgrid are identified. 
     
     
         11 . The method of  claim 7 , wherein transfer terms between nodes are assigned on a nodal basis to the nodes of the subgrids. 
     
     
         12 . The method of  claim 11 , wherein the transfer terms include initial pore pressures, fluid distributions and volumes. 
     
     
         13 . The method of  claim 11 , wherein the characterized pore types include at least one of each of the porosity types of natural fracture pore systems, matrix pore systems, induced fracture pore systems and vug pore systems, and wherein the zone includes at least one node of each porosity type. 
     
     
         14 . The method of  claim 1 , wherein the step of solving the linear system comprises selecting non-linear equations to represent the modeled reservoir; and linearizing the nonlinear equations for subsequent solving using the linear solver. 
     
     
         15 . The method of  claim 1 , wherein the characterized pore types are utilized to create one or more subgrids that represent a zone within the reservoir, and wherein the linear solver is applied by subgrid or associated subgrids. 
     
     
         16 . The method of  claim 1 , wherein the step of solving a linear system is iterated utilizing the resultant magnitudes until a desired degree of convergence is achieved between the linear and non-linear equations. 
     
     
         17 . The method of  1 , further comprising the step of altering the wellbore pressure of the model to achieve a desired level of mass transfer and fluid flow for the modeled reservoir. 
     
     
         18 . A computer program product comprising non-transitory computer-readable medium having stored thereon instructions executable by a computer for causing the computer perform simulation of a reservoir represented by a model having a plurality of porosity nodes, the instructions for causing the computer to:
 characterizing at least three different porosity types for the modeled reservoir, the at least three different porosity types selected from the group consisting of natural fracture pore systems, matrix pore systems, induced fracture pore systems and vug pore systems;   identifying transfer terms between the nodes of at least three porosity types; and   solving a linear system for the model using a linear solver.   
     
     
         19 . The computer program product of  claim 18 , wherein the characterized pore types include at least one of each of the porosity types of natural fracture pore systems, matrix pore systems, induced fracture pore systems and vug pore systems, wherein the characterized pore types are utilized to create one or more subgrids that represent a zone within the reservoir, and wherein the zone includes at least one node of each porosity type. 
     
     
         20 . The computer program product of  claim 19 , wherein transfer terms between nodes are assigned on a nodal basis to the nodes of the subgrids. 
     
     
         21 . The computer program product of  claim 21 , wherein the linear solver is applied by subgrid or associated subgrids. 
     
     
         22 . A method for drilling one or more wellbores in shale reservoir, which method comprises:
 modeling an oil and gas shale reservoir having natural fracture pore systems, matrix pore systems, induced fracture pore systems and vug pore systems;   characterizing at least three different porosity types in the modeled reservoir, wherein the characterized pore types are utilized to create one or more subgrids that represent a zone within the reservoir, and wherein the zone includes at least one node of each porosity type;   assigning transfer terms between the at least three porosity types, wherein transfer terms between nodes are assigned on a nodal basis to the nodes of the subgrids; and   solving a linear system for the model using a linear solver;   preparing equipment to construct a portion of said wellbore;   based on the modeled reservoir, selecting a characteristic for the wellbore; and   drilling a wellbore in accordance with the selected characteristic.   
     
     
         23 . The method of  claim 22 , wherein the selected characteristic is the trajectory of the wellbore. 
     
     
         24 . The method of  claim 22 , wherein the selected characteristic is the pressure of the wellbore. 
     
     
         25 . The method of  claim 24 , further comprising the step of iteratively altering the wellbore pressure of the model to identify a wellbore pressure at which a desired level of mass transfer and fluid flow for the modeled reservoir is achieved; and utilizing the identified wellbore pressure as the selected characteristic. 
     
     
         26 . The method of  claim 22 , further comprising the steps of drilling a first wellbore in the reservoir; recording values associated with mass transfer and fluid flow around the first wellbore; and utilizing the recorded vales as the values associated with a portion of the assigned transfer terms between the at least three porosity types; and drilling a second wellbore in the reservoir, wherein the second wellbore is the wellbore drilled in accordance with the selected characteristic. 
     
     
         27 . The method of  claim 22 , wherein the characterized pore types include at least one of each of the porosity types of natural fracture pore systems, matrix pore systems, induced fracture pore systems and vug pore systems, wherein the characterized pore types are utilized to create one or more subgrids that represent a zone within the reservoir, and wherein the zone includes at least one node of each porosity type. 
     
     
         28 . The method of  claim 27 , wherein transfer terms between nodes are assigned on a nodal basis to the nodes of the subgrids. 
     
     
         29 . The method of  claim 28 , wherein the linear solver is applied by subgrid or associated subgrids.