Assessing the Validity and Limitations of Dual-porosity Models Using Geological Well Testing for Fractured Formations

Egya, David; Geiger, Sebastian; Corbett, Patrick William Michael; Bisdom, Kevin; Bertotti, Giovanni; Bezerra, Hélio Nogueira

doi:10.3997/2214-4609.201601449

Cited by 4 publications

(2 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The presented workflow enables fast generation of highly detailed realistic fracture networks for use of geomechanical and flow modelling, variations of which have been applied to study different aspects of fracture and fracturematrix flow (e.g. Aljuboori et al, 2015;Arnold et al, 2016;Bisdom et al, 2016c;Egya et al, 2016;Muhammad, 2016;Shah et al, 2016).…”

Section: Discussionmentioning

confidence: 99%

“…These flow models also help to identify different fracture-matrix permeability domains, which can be used to better characterise fractured reservoir flow domains. To further bridge the gap between discrete fracture models and reservoir-scale continuum models, hybrid upscaling techniques can be used (Egya et al, 2016;Shah et al, 2016).…”

Section: Lessons For Reservoir-scale Flow Modellingmentioning

confidence: 99%

See 1 more Smart Citation

An integrated workflow for stress and flow modelling using outcrop-derived discrete fracture networks

Bisdom

Nick

Bertotti

2017

Computers & Geosciences

Self Cite

View full text Add to dashboard Cite

Fluid flow in naturally fractured reservoirs is often controlled by subseismic-scale fracture networks. Although the fracture network can be partly sampled in the direct vicinity of wells, the inter-well scale network is poorly constrained in fractured reservoir models. Outcrop analogues can provide data for population of domains of the reservoir model where no direct measurements are available. However, extracting relevant statistics from large outcrops representative of inter-well scale fracture networks remains challenging. Recent advances in outcrop imaging provide high-resolution datasets that can cover areas of several hundred by several hundred meters, i.e. the domain between adjacent wells, but even then, data from the high-resolution models is often upscaled to reservoir flow grids, resulting in loss of accuracy. We present a workflow that uses photorealistic georeferenced outcrop models to construct geomechanical and fluid flow models containing thousands of discrete fractures covering sufficiently large areas, that does not require upscaling to model permeability. This workflow seamlessly integrates geomechanical Finite Element models with flow models that take into account stress-sensitive fracture permeability and matrix flow to determine the full permeability tensor. The applicability of this workflow is illustrated using an outcropping carbonate pavement in the Potiguar basin in Brazil, from which 1082 fractures are digitised. The permeability tensor for a range of matrix permeabilities shows that conventional upscaling to effective grid properties leads to potential underestimation of the true permeability and the orientation of principal permeabilities. The presented workflow yields the full permeability tensor model of discrete fracture networks with stress-induced apertures, instead of relying on effective properties as most conventional flow models do.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Lessons For Reservoir-scale Flow Modellingmentioning

confidence: 99%

An integrated workflow for stress and flow modelling using outcrop-derived discrete fracture networks

Bisdom

Nick

Bertotti

2017

Computers & Geosciences

Self Cite

View full text Add to dashboard Cite

show abstract

Analysing the limitations of the dual-porosity response during well tests in naturally fractured reservoirs

Egya

Geiger

Corbett

et al. 2018

View full text Add to dashboard Cite

Geological reservoirs can be extensively fractured but the well-test signatures observed in the wells may not show a pressure transient response that is representative of naturally fractured reservoirs (NFRs): for example, one that indicates two distinct pore systems (i.e. the mobile fractures and immobile matrix). Yet, the production behaviour may still be influenced by these fractures. To improve the exploitation of hydrocarbons from NFRs, we therefore need to improve our understanding of fluid-flow behaviour in fractures. Multiple techniques are used to detect the presence and extent of fractures in a reservoir. Of particular interest to this work is the analysis of well-test data in order to interpret the flow behaviour in an NFR. An important concept for interpreting well-test data from an NFR is the theory of dual-porosity model. However, several studies pointed out that the dual-porosity model may not be appropriate for interpreting well tests from all fractured reservoirs. This paper therefore uses geological well-testing insights to explore the limitations of the characteristic flow behaviour inherent to the dual-porosity model in interpreting well-test data from Type II and III NFRs of Nelson's classification. To achieve this, we apply a geoengineering workflow with discrete fracture matrix (DFM) modelling techniques and unstructured-grid reservoir simulations to generate synthetic pressure transient data in both idealized fracture geometries and real fracture networks mapped in an outcrop of the Jandaira Formation. We also present key reservoir features that account for the classic V-shape pressure derivative response in NFRs. These include effects of fracture skin, a very tight matrix permeability and wells intersecting a minor, unconnected fracture close to a large fracture or fracture network. Our findings apply to both connected and disconnected fracture networks.

show abstract

Step Rate Test as a Way to Understand Well Performance in Fractured Carbonates

Shchipanov

Kollbotn

Prosvirnov

2017

SPE Europec Featured at 79th EAGE Conference and Exhibition

View full text Add to dashboard Cite

Step Rate Test (SRT) is commonly used to estimate formation parting (or fracture opening) pressure for stimulated wells. SRTs may also focus on changes of well performance at different rates / pressures that is of special interest for stress-sensitive reservoirs such as fractured carbonates. Installation of permanent downhole gauges (PDG) and running SRTs on injection wells at the Ekofisk field gave a chance to improve the understanding of reservoir and well performance. Analysis of these SRTs also resulted in further development of SRT interpretation techniques. An approach to SRT interpretation, combining analytical pressure-rate (p-Q) curve analysis and step-by-step Pressure Transient Analysis (PTA) with numerical simulation of SRT, was suggested and tested. Applying this approach to Ekofisk SRTs has shown that the p-Q analysis may be used for diagnostics of well performance changes, while step-by-step PTA enables decomposing of well (skin factor) and reservoir (conductivity) effects with estimation of corresponding well-reservoir parameters as pressure or rate functions. Numerical simulation confirmed that pressure dependent conductivity estimated from the step-by-step PTA is the governing factor in matching SRT history. Special attention was paid to the uniqueness of SRT interpretation using suggested approach. Reaching infinite acting radial flow (IARF) regime at each step of a test provided unique parameter estimates as shown by example of a stimulated slanted injector. Being too far from IARF at end of each step will make the interpretations more uncertain. Different sets of changing parameters estimated from SRT interpretation could provide satisfactory match in numerical runs as was illustrated by example of a horizontal injector with multiple induced fractures. Comparison of interpretation results for different wells integrating additional field data is a possible way to reduce this uncertainty. Finally, some hints to designing, conducting and interpreting SRTs of different types of wells in fractured carbonate fields are given, using Ekofisk field experience.

show abstract

Assessing the Validity and Limitations of Dual-porosity Models Using Geological Well Testing for Fractured Formations

Cited by 4 publications

References 0 publications

An integrated workflow for stress and flow modelling using outcrop-derived discrete fracture networks

An integrated workflow for stress and flow modelling using outcrop-derived discrete fracture networks

Analysing the limitations of the dual-porosity response during well tests in naturally fractured reservoirs

Step Rate Test as a Way to Understand Well Performance in Fractured Carbonates

Contact Info

Product

Resources

About