Shale Stability: Drilling Fluid Interaction and Shale Strength

Lal, Manohar

doi:10.2523/54356-ms

Cited by 35 publications

(31 citation statements)

References 7 publications

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“…In the oil and gas industry, 75% of all footage was drilled in shale formations which are responsible for 90% of wellbore stability problems [1][2][3]. The main cause of shale instability for both soft and hard shales is water absorption and the subsequent swelling and sloughing of the wellbore [4].…”

Section: Introductionmentioning

confidence: 99%

2D Numerical Simulation of Improving Wellbore Stability in Shale Using Nanoparticles Based Drilling Fluid

Song

Yuan²,

et al. 2017

Energies

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Abstract:The past decade has seen increased focus on nanoparticle (NP) based drilling fluid to promote wellbore stability in shales. With the plugging of NP into shale pores, the fluid pressure transmission can be retarded and wellbore stability can be improved. For better understanding of the interaction between shale and NP based drilling fluid based on previous pressure transmission tests (PTTs) on Atoka shale samples, this paper reports the numerical simulation findings of wellbore stability in the presence of NP based drilling fluid, using the 2D fluid-solid coupling model in FLAC3D™ software. The results of previous PTT are discussed first, where the steps of numerical simulation, the simulation on pore fluid pressure transmission, the distribution of stress and the deformation of surrounding rock are presented. The mechanisms of NP in reducing permeability and stabilizing shale are also discussed. Results showed that fluid filtrate from water-based drilling fluid had a strong tendency to invade the shale matrix and increase the likelihood of wellbore instability in shales. However, the pore fluid pressure near wellbore areas could be minimized by plugging silica NP into the nanoscale pores of shales, which is consistent with previous PTT. Pore pressure transmission boundaries could also be restricted with silica NP. Furthermore, the stress differential and shear stress of surrounding rock near the wellbore was reduced in the presence of NP. The plastic yield zone was minimized to improve wellbore stability. The plugging mechanism of NP may be attributed to the electrostatic and electrodynamic interactions between NP and shale surfaces that are governed by Derjaguin-Landau-Verwey-Overbeek (DLVO) forces, which allowed NP to approach shale surfaces and adhere to them. We also found that discretization of the simulation model was beneficial in distinguishing the yield zone distribution of the surrounding rock in shales. The combination of PTT and the 2D numerical simulation offers a better understanding of how NP-based drilling fluid can be developed to address wellbore stability issues in shales.

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Section: Introductionmentioning

confidence: 99%

2D Numerical Simulation of Improving Wellbore Stability in Shale Using Nanoparticles Based Drilling Fluid

Song

Yuan²,

et al. 2017

Energies

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“…Shale is a typical anisotropic rock which contains structural discontinuities such as natural fractures and bedding planes [1]. Shale gas production often encounters drilling problems, such as hole collapses, stuck pipes and fracturing [2]. During the drilling process, stresses are redistributed at and near the bore-hole walls, the initiation and propagation of fractures occurs and this further affects the strength and permeability evolution [3].…”

Section: Introductionmentioning

confidence: 99%

“…The shale strength is influenced by many factors, such as the physical properties (e.g., compaction, porosity, density, permeability, mineralogy, water content) and the stress environment (e.g., drilling-induced stress paths, drilling fluid, pore pressure) [2]. The compaction history plays an important role in the shale strength.…”

Section: Introductionmentioning

confidence: 99%

“…The compaction history plays an important role in the shale strength. During the compaction process, grain clays are compacted and this results in excessive pore pressures, pore water is expelled and pore connectivity through pore throats decreases, strength increases and also the porosity and permeability decrease [2]. The shale strength is positively correlated with density.…”

Section: Introductionmentioning

confidence: 99%

“…The water along with the cracks infiltrates the shale grain and weakens the link between the grains so that it reduces the shale strength [6]. During the drilling process, stresses are redistributed, as the stress increases in the vertical direction and decreases in the horizontal direction, the effective confining pressure decreases and this causes the shale strength to decrease [2]. In addition, due to the low permeability of the shale-gas reservoirs, hydraulic fracturing is widely applied in the development of shale gas.…”

Section: Introductionmentioning

confidence: 99%

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Failure Criteria of Gas-Infiltrated Sandy Shale Based on the Effective Stress Principle

Zhang

2016

Energies

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Pore gas has a significant influence on rock strength. This study performed triaxial compression tests of gas-infiltrated sandy shale samples to investigate the strength characteristics under gas pressures of 0 and 2 MPa. The effective stress coefficient was evaluated while considering the gas and solid coupling effect, and was found to decrease with increasing confining pressure. The calculated and different assumed coefficient values (0 and 1) were applied to obtain the effective principal stress. The experimental results would serve as fundamental strength data for fitting analysis in failure criterion work. The Mohr-Coulomb, Hoek-Brown, Drucker-Prager, linear Mogi, and non-linear Mogi criteria were modified based on the effective stress principle of porous rock. In addition, the RMSE, cohesion, and internal friction angle were utilized for a quantitative criterion comparison. The results showed that the Mohr-Coulomb, Drucker-Prager, and linear Mogi failure criteria led to higher errors, whereas the Hoek-Brown criterion gave an apparent distortion as a result of the empirical strength parameters. Moreover, the non-linear Mogi criterion showed a good fit. The predicted strength was overestimated when α = 0 and underestimated when α = 1, with a more accurate strength estimated when the effective stress coefficient was calculated using the effective stress principle.

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Stress magnitude and orientation in the Potiguar Basin, Brazil: Implications on faulting style and reactivation

et al. 2013

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[1] We analyzed borehole breakout data and drilling-induced tensile fractures derived from resistivity image logs run at 10 oil wells to derive the orientation of the maximum horizontal stress S Hmax from the Potiguar Basin in the continental margin of Brazil. Stress magnitudes are derived from density logs for the vertical stress, mini-frac tests for the minimum horizontal stress S hmin , and rock strength laboratory analysis to estimate the S Hmax magnitudes. We compared these results with the stress regime and S Hmax orientation derived from nine earthquake series located in the crystalline basement, where seismicity is concentrated, and previous breakout data from the basin. In the basin, the S Hmax gradient is 20.0 MPa/km, and the S Hmax /S hmin ratio is 1.154, indicating a normal tectonic stress regime from 0.5 to 2.0 km, whereas the S Hmax gradient of 24.5 MPa/km and S Hmax /S hmin ratio of 1.396 indicate a transition from a normal to strike-slip stress regime at 2.5 to 4.0 km. The deeper stress regime in the basin is similar to that in the basement at 1-12 km depth. This transition of the tectonic stress regime is consistent with an incipient tectonic inversion in the basin. We note that the S Hmax orientation rotates from NW-SE in the western part of the Potiguar Basin to E-W in its central and eastern parts, roughly following the shoreline geometry, indicating that local features such as flexural stresses influence the local (scale < 100 km) stress pattern. We also conclude that the basement is critically stressed, but not the basin.

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Shale Stability: Drilling Fluid Interaction and Shale Strength

Cited by 35 publications

References 7 publications

2D Numerical Simulation of Improving Wellbore Stability in Shale Using Nanoparticles Based Drilling Fluid

2D Numerical Simulation of Improving Wellbore Stability in Shale Using Nanoparticles Based Drilling Fluid

Failure Criteria of Gas-Infiltrated Sandy Shale Based on the Effective Stress Principle

Stress magnitude and orientation in the Potiguar Basin, Brazil: Implications on faulting style and reactivation

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