Coupled geomechanics–flow modelling at and below a critical stress state used to investigate common statistical properties of field production data

Abstract

An areal model of a fractured/faulted reservoir with 49 wells is developed that incorporates fully-coupled geo-mechanics and fluid flow. It is a generic example of a pattern waterflood although it is inspired by a parallel study of the Gullfaks reservoir in the North Sea, in which stress-related, fault-related and long-range correlations in rate fluctuations are observed. Based on this model, three scenarios are examined in terms of different initial stress states prior to production, each of which involves 36 months of production and injection in the presence of fracture sets and faults. The results support the concept that the long-range, stress-related and fault-related characteristics of correlations in rate fluctuations, observed not only in the Gullfaks data, but also in several other fields worldwide, are symptomatic of a system near a geomechanical critical point. These characteristics are not observed in models that are sub-critical. Short-range rate correlations are likely to exist where there are highly permeable zones between producers and injectors. Long-range rate correlations occur only within critically-stressed regions where there is active shearing or fault reactivation. The modelling results are consistent with field evidence suggesting that incipient shearing is an important mechanism coupled with reservoir flow behaviour.

A study of injection-induced mechanical deformation at the In Salah CO2 storage project

“…9). Although, more typically values of 1 GPa/m or more are assumed for fault normal stiffness (e.g., Zhang et al, 2008) some authors have considered faults with stiffnesses less than 0.1 GPa/m in sedimentary materials (Matsuki et al, 2009). Considering the results in Fig.…”

The challenges and impact of compartmentalization in reservoir appraisal and development

“…Møller-Pedersen & Koestler 1997;Coward et al 1998;Jones et al 1998;Nieuwland 2003;McClay 2004;Swennen et al 2004;Boult & Kaldi 2005;Shaw 2005;Sorkhabi & Tsuji 2005;, Jolley et al 2007aLonergan et al 2007;Wibberley et al 2008a). In understanding the uncertainties and risks from compartmentalization these largely lie in the areas of: reservoir scale structural analysis Dee et al 2005;Fossen & Bale 2007); fault and fracture growth, fault zone architecture and characterization Wibberley et al 2008b); fault seal prediction (Bretan et al 2003;Dee et al 2007); the incorporation of faults and fault zone properties in reservoir models and simulation (Manzocchi et al 1999(Manzocchi et al , 2002(Manzocchi et al , 2008Harris et al 2005Harris et al , 2007Childs et al 2007;Fisher & Jolley 2007;Zijlstra et al 2007); integrated fluid description (Smalley & England 1994;Larter & Aplin 1995;Smalley et al 2004); the use of geomechanical data along with field and inter-well scale stress and strain analysis and modelling -incorporating the use of micro-seismicity for surveillance (Heffer 2002;Rutledge et al 2004;Sanderson & Zhang 2004;Main et al 2007;Zhang et al 2007;Osorio et al 2008). …”

“…However, whilst it is unlikely that we will ever be able to predict actual individual fault and fracture distributions at the core scale across a reservoir, there have been advances in developing analytical proxies. The advent of high performance computing capability enables advances in numerical geomechanical modelling techniques together with rock property studies (Koutsabeloulis & Hope 1998;Nieuwland 2003;Zhang et al 2007). Resulting numerical stress and strain simulation and forward prediction capabilities offer the opportunity to better model the spatial distribution of the processes controlling the formation of faults and fractures (McClay et al 2002;Main et al 2007;Wilkins 2007).…”

“…We are now beginning to place a greater emphasis on capturing appropriate ranges of geological scenarios and associated uncertainty ranges, with the incorporation of dynamic signals from production data (Bentley & Smith 2008;Smalley et al 2008). Evidence is also mounting that as fields deplete under production they evolve mechanically: leading to changes in injectorproducer well communication; fault seal integrity; fault zone conductivity; fracture permeability; near and far-field stress configurations and orientations; and reservoir permeability heterogeneity (Heffer et al 1995;Heffer 2002;Main et al 2006;Zhang et al 2007). These effects are commonly not predicted at the early stages of field development.…”

Effective stress history and the potential for seismicity associated with hydraulic fracturing of shale reservoirs

“…A series of papers by Heffer and other researchers concerning oilfield waterflood correlations (e.g. Heffer & Dowokpor 1990;Heffer et al 1994;Zhang et al 2007) prompted Maillot et al (1999) to develop a numerical model of the initiation, growth and radiation of shear failures induced by pore pressure changes in a poroelastic medium. Otherwise, simulation of stress transmission is either confined to the seismogenic source structure and greatly simplified using a Burridge-Knopoff model (Baisch et al 2009) or omitted (e.g.…”