Factors Critical to Multiwell Reservoir Simulation of Liquids-Rich Shale Plays
Authors: Wilson Adam 
Published: February 2015

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 169025, ’A Study of Dynamic and Static Factors That Are Critical to Multiwell Reservoir Simulation of Liquids-Rich Shale Plays,’ by Carlos Miranda, SPE, and Huade Yang, Marathon, prepared for the 2014 SPE Unconventional Resources Conference - USA, The Woodlands, Texas, USA, 1-3 April. The paper has not been peer reviewed.

Multiwell modeling of shale plays is not performed frequently, mainly for two reasons: The requirements to capture the behavior of multiple horizontal wells with multiple hydraulic fractures could be computationally prohibitive, and the wells in extremely low- permeability formations would have minimal interaction. Production data collected from shale plays, however, have shown that horizontal wells may interfere with each other during production. Therefore, in projects in which a main objective is well spacing or completion optimization, a comprehensive multiwell reservoir-simulation study is required.

Introduction

Single-well reservoir modeling has been used extensively to perform reservoir simulation in shale formations. In the appraisal phase of liquids-rich shale (LRS) reservoir systems, more detail may be required to capture petrophysical and stratigraphic features that can potentially affect production performance. During this phase, single-well conceptual models with a certain degree of detail can be sufficient for modeling purposes and economic analysis. However, if the presence of geological features (e.g., faults, fracture corridors, contrast of areal and vertical distribution of natural-fracture intensity) is believed to affect the economic evaluation of a certain area of interest, then a more-detailed geological model is required and multiple wells may have to be incorporated in the models.

Performing multiwell, or sector, modeling of shale formations can present several challenges:

An adequate description of permeability and water saturation may be difficult to attain because the original values are considerably altered in the stimulated-rock-volume (SRV) region after the fracturing treatments.

The capture of the transient flow observed in LRS formations and the large pressure gradients around the fracture planes requires extensive grid refinement.

The large drawdown necessary to produce from these ultralow-permeability formations can make pressure/ volume/temperature (PVT) sampling a poor representation of the original reservoir conditions.

The interaction of hydraulic fractures with natural fractures or the development of fracture networks can be very difficult to model.

Seismic

The application of seismic for reservoir simulation of LRS plays goes beyond the classical reservoir-simulation workflow; seismic processing, inversion, and interpretation can provide important reservoir- property distributions that are key parameters for reservoir simulation and production analysis.

A variety of seismic attributes can be used to predict the intensity and orientation of probable pre-existing natural fractures and the correlation with microseismic responses. This can be used to build discrete-fracture-network (DFN) models and patterns of hydraulic-fracture propagation and interaction with natural fractures and to constrain the SRV size and shape.

Acoustic impedance can be used to generate porosity and pore-pressure distributions within a target shale region. The logic is that acoustic impedance is a linear function of density, and density can be correlated with porosity from a petrophysical model.

Seismic interpretation calibrated with rock-property models is also used to provide rock-property distribution in a specific area to constrain and validate production from reservoir-simulation models.