The representation of two phase fault-rock properties in flow simulation models

Abstract

Faults are represented conventionally in production flow simulation models using transmissibility multipliers which capture the single phase, but not the two phase, fault-rock properties. Available data indicate that fault-rocks have similar two phase properties to sediments of the same permeability, hence existing methods can be applied to estimate two phase fault-rock properties from their intrinsic permeabilities. Two methods of representing the two phase fault-rock properties implicitly in the flow simulator are compared, using one-dimensional numerical flow models containing water-wet faults with imbibition capillary pressure curves. The method which is the closer two phase analogue of the single phase transmissibility multiplier is inappropriate, as the implementation is unreasonably unwieldy. A simpler implementation is to derive pseudo-relative permeability functions including the fault-rock properties in the upstream grid block; these properties are then incorporated directly in the simulator. Relative transmissibility multiplier functions can be back-calculated from the pseudo-relative permeability functions, and indicate how closely the single phase multiplier approximates two phase flow through the fault. Implementation in a 3D model with complex fault juxtapositions validates the approach, and a practical workflow for the routine inclusion of two phase fault-rock properties in conventional faulted flow simulation models is outlined.

Structurally complex reservoirs: an introduction

“…Zijlstra et al present flow data from a number of faulted reservoirs suggesting that two-phase flow properties of the faults are important in controlling compartmentalization of fluid production. They support their conclusions by presenting the results of a method for fault property modelling which is easy to implement and accounts for some of the effects of fault-related single phase and multiphase flow (as described by Manzocchi et al 1999Manzocchi et al , 2002.…”

“…In these circumstances, the faults are detrimental to flow, acting as baffles or barriers within a generally more permeable host rock sedimentary sequence (e.g. Knipe 1993;Downey 1994;Knipe et al 1997, Yielding et al 1997Jones et al 1998;Manzocchi et al 1999Manzocchi et al , 2002Hesthammer & Fossen 2000;Brown 2003;James et al 2004). Issues such as the primary connectivity of reservoir units will also impact the behaviour of the flow system.…”

“…For example, Manzocchi et al (1999Manzocchi et al ( , 2002 provided robust methods with which it is possible to invoke these algorithms, to incorporate the flow-retarding effects of faults systematically. Their methods calculate geologically realistic fault transmissibility multipliers from the upscaled model geometry and geo-cellular properties (e.g.…”

“…Traditionally, the multi-phase flow properties of faults have not been included during production simulation modelling, although several key publications have highlighted their importance (e.g. Manzocchi et al 1998Manzocchi et al , 2002Manzocchi 1999;Rivenaes & Dart 2002;Al-Busafi et al 2005). A recent innovation in fault handling within reservoir models is the development by Manzocchi et al (2002) of a method for the inclusion of the two-phase flow properties of faults.…”

“…Manzocchi et al 1998Manzocchi et al , 2002Manzocchi 1999;Rivenaes & Dart 2002;Al-Busafi et al 2005). A recent innovation in fault handling within reservoir models is the development by Manzocchi et al (2002) of a method for the inclusion of the two-phase flow properties of faults. Because two-phase properties, unlike single fluid phase properties, cannot be attached to the face of grid blocks in reservoir simulations, this method derives pseudo-relative permeability functions including the fault rock properties in the upstream grid block for cross-fault flow.…”