Coupled fluid flow-geomechanics simulation in stress-sensitive coal and shale reservoirs: Impact of desorption-induced stresses, shear failure, and fines migration

Abstract Unconventional shale reservoirs are characterized by low porosity and ultra-low permeability. Natural fractures are known to be present and considered a critical factor for the enhanced post-stimulation productivity. Accounting for natural fractures with existing techniques has not been widely adopted owing to their complexity or lack of validation. Ongoing research efforts are striving to understand how natural fractures can be accounted for and accurately modeled in fluid flow of the subject reservoirs. This study utilized Eagle Ford well data comprising reservoir properties, stimulation metrics, production, microseismicity and permeability measurements from a core plug. The methodology comprised use of production data to extract a linear flow regime parameter. This was coupled with fracture geometry, predicted from hydraulic fracture modeling and microseismicity, to estimate the system permeability. From interpreting microseismic events as slips on critically stressed natural fractures, explicit modeling incorporating a discrete fracture network (DFN) assumed activated natural fractures supplement conductive reservoir contact area. Thus, allowed the estimation of matrix permeability. For validation, the aforementioned was compared with core plug permeability measurements. Results from modeling of planar hydraulic fractures, with microseismicity as validation, predicted planar fracture geometry which when coupled with the linear flow parameter resulted in a system permeability. Incorporation of DFNs to account for activated natural fractures yielded matrix permeability in picodarcy range. A review of laboratory permeability measurements exhibited stress dependence with the value at the maximum experimental confining pressure of 4000 psi in the same range as the computed system permeability. However, the confining pressures used in the experiments were less than the in situ effective stress. Correction for representative stress yielded an ultra-low matrix permeability in the same range as the DFN-based picodarcy matrix permeability. Thus, supporting the adopted drainage architecture and often suggested role of natural fractures in shale reservoir fluid flow. This study presents a multi-discipline workflow to account for natural fractures, and contributes to understanding that will improve laboratory petrophysics and the overall reservoir characterization of the subject reservoirs. Given that the Eagle Ford is an analogue of emerging shales elsewhere, results from this study can be widely adopted.

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Matrix permeability and flow-derived DFN constrain reactivated natural fracture rupture area and stress drop — Marcellus Shale microseismic example

The Leading Edge ◽

10.1190/tle40090667.1 ◽

2021 ◽

Vol 40 (9) ◽

pp. 667-676

Author(s):

Clay Kurison ◽

Huseyin S. Kuleli

Keyword(s):

Fluid Flow ◽

Pore Pressure ◽

Stress Drop ◽

Marcellus Shale ◽

Linear Flow ◽

Matrix Permeability ◽

Rupture Area ◽

Microseismic Events ◽

Shale Reservoirs ◽

Stress Drops

Microseismic events associated with shale reservoir hydraulic fracturing stimulation (HFS) are interpreted to be reactivations of ubiquitous natural fractures (NFs). Despite adoption of discrete fracture network (DFN) models, accounting for NFs in fluid flow within shale reservoirs has remained a challenge. For an explicit account of NFs, this study introduced the use of seismology-based relations linking seismic moment, moment magnitude, fault rupture area, and stress drop. Microseismic data from HFS monitoring of Marcellus Shale horizontal wells had been used to derive planar hydraulic fracture geometry and source properties. The former was integrated with associated well production data found to exhibit transient linear flow. Analytical solutions led to linear flow parameters (LFPs) and system permeability for scenarios depicting flow through infinite and finite conductivity hydraulic fractures. Published core plug permeability was stress-corrected for in-situ conditions to estimate average matrix permeability. For comparison, the burial and thermal history for the study area was used in 1D Darcy-based modeling of steady and episodic expulsion of petroleum to account for geologic timescale persistence of abnormal pore pressure. Both evaluations resulted in matrix permeability in the same picodarcy (pD) range. Coupled with LFPs, reactivated NF surface area for stochastic DFNs was estimated. Subsequently, the aforementioned seismology-based relations were used for determining average stress drops needed to estimate NF rupture area matching flow-based DFN surface areas. Stress drops, comparable to values for tectonic events, were excluded. One of the determined values matched stress drops for HFS operations in past and recent seismological studies. In addition, calculated changes in pore pressure matched estimates in the aforementioned studies. This study unlocked the full potential of microseismic data beyond extraction of planar geometry attributes and stimulated reservoir volume (SRV). Here, microseismic events were explicitly used in the quantitative account of NFs in fluid flow within shale reservoirs.

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The role of stress history on the flow of fluids through fractures

Mineralogical Magazine ◽

10.1180/minmag.2012.076.8.30 ◽

2012 ◽

Vol 76 (8) ◽

pp. 3165-3177 ◽

Cited By ~ 19

Author(s):

S. Sathar ◽

H. J. Reeves ◽

R. J. Cuss ◽

J. F. Harrington

Keyword(s):

Shear Stress ◽

Fluid Flow ◽

Gas Flow ◽

Shear Failure ◽

Normal Load ◽

Damage Zone ◽

Water Injection ◽

Fracture Flow ◽

Stress History ◽

Stress Regime

AbstractUnderstanding flow along fractures and faults is of importance to the performance assessment (PA) of a geological disposal facility (GDF) for radioactive waste. Flow can occur along pre-existing fractures in the host-rock or along fractures created during the construction of the GDF within the excavation damage zone (EDZ). The complex fracture network will have a range of orientations and will exist within a complex stress regime. Critical stress theory suggests that fractures close to localized shear failure are critically stressed and therefore most conductive to fluid flow. Analysis of fault geometry and stress conditions at Sellafield has revealed that no features were found to be, or even close to being, classified as critically stressed, despite some being conductive. In order to understand the underlying reasons why non-critically stressed fractures were conductive a series of laboratory experiments were performed. A bespoke angled shear rig (ASR) was built in order to study the relationship between fluid flow (water and gas) through a fracture surface as a function of normal load. Fluid flow reduced with an increase in normal load, as expected. During unloading considerable hysteresis was seen in flow and shear stress. Fracture flow was only partially recovered for water injection, whereas gas flow increased remarkably during unloading. The ratio of shear stress to normal stress seems to control the fluid flow properties during the unloading stage of the experiment demonstrating its significance in fracture flow. The exhumation of the Sellafield area during the Palaeogene–Neogene resulted in considerable stress relaxation and in fractures becoming non-critically stressed. The hysteresis in shear stress during uplift has resulted in faults remaining, or becoming, conductive. The field and laboratory observations illustrate that understanding the stress-history of a fractured rock mass is essential, and a mere understanding of the current stress regime is insufficient to estimate the flow characteristics of present-day fractures.

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A Numerical Study of Turbulence Generation and Induced Stresses in Pressure Reducing Orifice

Volume 4: Fluid-Structure Interaction ◽

10.1115/pvp2014-29110 ◽

2014 ◽

Author(s):

Mahmoud M. M. Gabr ◽

Maher Y. A. Younan ◽

Ahmed M. R. El-Baz

Keyword(s):

Fluid Flow ◽

Safety Factor ◽

System Reliability ◽

Pipe Wall ◽

Numerical Study ◽

Plate Thickness ◽

The Other ◽

Induced Stresses ◽

And Performance ◽

Turbulence Generation

In the present paper, a numerical fluid flow and induced stresses are studied for single hole and multi-hole orifice plates. Three multi hole configurations are studied; orifice with 3 holes, 5 holes and 7 holes. Turbulence characteristics behind each configuration are analyzed and orifice geometry strength and safety factor are assessed. The multi-hole orifice showed promising results in reducing the turbulence which would increase the system reliability and performance. On the other hand, multi-hole orifice showed weaker strength for same orifice plate thickness and higher probability for pipe wall erosion.

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Reduction of Fines Migration by Nanofluids Injection: An Experimental Study

SPE Journal ◽

10.2118/144196-pa ◽

2012 ◽

Vol 18 (02) ◽

pp. 309-318 ◽

Cited By ~ 42

Author(s):

A.. Habibi ◽

M.. Ahmadi ◽

P.. Pourafshary ◽

Sh.. Ayatollahi ◽

Y.. Al-Wahaibi

Keyword(s):

Fluid Flow ◽

Porous Materials ◽

Packed Column ◽

Solid Particles ◽

Permeability Reduction ◽

Fines Migration ◽

High Tendency ◽

Migration Effect ◽

The Matrix ◽

Productivity Decline

Summary Formation damage of oil reservoirs as a result of fines migration is a major reason for productivity decline. Formation fines are defined as unconfined solid particles present in the pore spaces of formations. Their migration, caused by fluid flow in the reservoir, can cause pore plugging and permeability reduction. In the last 3 decades, many studies have characterized fines and their migration effect on permeability reduction. There are many techniques in the industry to remediate the damage, especially in the near-wellbore region. Nanofluids (NFs) that contain nanoparticles (NPs) exhibit specific properties, including a high tendency for adsorption and being good candidates for injection into the near-wellbore region, because of the small nanoparticle sizes. In this paper, a packed column is used to study the use of different types of NPs to reduce fines migration in synthetic porous materials. Three types of NPs—MgO, SiO2, and Al2O3—are used here to investigate their effects on fines movement. The results indicate that fines may adhere to the matrix grains, hindering their migration, when the porous materials are soaked with NFs. Furthermore, to check the mechanisms of this remediation technique, the effect of nanoparticle concentration and fluid flow rates in the medium on fines detachment was studied. A theoretical model was used to calculate total energy of interaction for the surfaces to check experimental results, which was also validated with scanning electron microscopy (SEM) pictures for samples from synthetic cores. The results showed that addition of 0.1 wt% of MgO and SiO2 NPs reduced fines migration by 15% compared with the reference state. MgO NPs were found to be more effective, even at high fluid rates, when used at a higher concentration, as noticed in the macroscopic and microscopic results.

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