Simulation and Analysis of Production Induced Reservoir Compaction using Geomechanical Formulation of Fracturing Technology (GFFT) for Stress Prediction
Authors: Haghi Amir Hossein , Kharrat Riaz , Asef M.R. 
Published: March 2015

For a depleting unconsolidated or poorly consolidated hydrocarbon reservoir, the decrease in reservoir pressure as a result of production would have a significant impact on the physical properties of the formation. Deformations commonly observed in producing reservoirs include compaction, fault reactivations and surface subsidence. Understanding the deformation mechanisms associated with these changes will have important implications for many aspects of oilfield development especially in reservoir management scheme.

In this paper, kirsch equations for the circular cavities and fracturing technology models in porous media have been used to estimate and predict the principle maximum and minimum reservoir stress by developing a Geomechanical Formulation of Fracturing Technology (GFFT). The curve of the least stress state versus reservoir pore pressure is used to assess the porosity loss using deformation analysis in reservoir space (DARS) formalism. Then, knowing the mechanism of production induced reservoir compaction in the reservoirs, porosity loss impact on reservoir productivity, investigates. Hence, numerical programming software's are employed for simulation, analysis and management process in different methods and scenarios. The reservoir data of the Ekofisk oil field located within the central Graben in the southern part of the Norwegian North Sea has been used as a case study in this research. While production from - injection into Ekofisk oil field, the pore pressure of the reservoirs have been changed. This effect caused reservoir compaction, porosity loss and correspondingly poroelastic parameter variations. Accordingly all these effects have been considered for stress estimation and after that evaluation of reservoir compaction and reservoir simulation.

Introduction:

The deformation of a reservoir in response to hydrocarbon production is important to understand for a variety of reasons. Slip on faults, as a result of a change in the in situ stress state, can pose serious problems in the field since it may cause casing failure (Maury et al., 1992) or a loss of sealing capacity of the reservoir bounding faults (e.g., Wiprut & Zoback, 1999).

Compaction associated with production will affect the rock properties of the formation, such as compressibility and permeability, and can significantly affect the results of reservoir simulation if neglected. Therefore, it is desirable to predict quantitatively the degree of compaction that accompanies depletion as well as the degree of permeability loss and, in some cases, the possibility of induced faulting or fault reactivation. While most existing models describing deformation associated with depletion are based on poroelastic theory, the heterogeneity of the reservoir and the inelastic nature of the formation are often ignored. The inelastic properties of the reservoir are especially important for poorly consolidated rock since such formations behave differently than their well-cemented counterpart. To fully understand the nature of deformation associated with production, a detailed study that includes both laboratory rock mechanic experiments, fields stress state and in situ reservoir conditions are required.