A realistic and integrated model for evaluating oil sands development with Steam Assisted Gravity Drainage technology in Canada

Influence of gravel on the propagation pattern of hydraulic fracture in the glutenite reservoir

Brittleness evaluation of coal based on statistical damage and energy evolution theory

Evaluating the ability of coal seams to form fracture networks by hydraulic fracturing is important for the development of coalbed methane (CBM) reservoirs. In this paper, a new index for evaluating coal brittleness was established from the perspective of energy evolution during coal failure. Uniaxial and triaxial compression tests of coal monitored by an acoustic emission (AE) system were carried out and the applicability of the new index and the influence of the confining pressure and cleat orientation on the coal brittleness were analyzed. The pre-peak and post-peak dissipated energies were the essential factors in determining the coal brittleness. The new index can characterize the influence of the external stress and cleat orientation on coal brittleness, and can also comprehensively reflect the mechanical properties of the coal during the pre-peak and post-peak stages. The corresponding AE energy curves can be divided into Rapid Fracture Type, Stable Fracture Type and Plastic Fracture Type. For the Rapid Fracture Type, the accumulation rate of AE energy showed sudden changes when reaching the yield stress and peak strength, which represented high brittleness. The Plastic Fracture Type represented low brittleness, and the accumulated AE energy curves were smooth—first concave and then convex. The brittleness index of coal studied in this paper can provide a new method for selecting the optimal CBM reservoir and optimizing the fracturing scheme.

Energy-Based Brittleness Index and Acoustic Emission Characteristics of Anisotropic Coal Under Triaxial Stress Condition

Water-weakening effect is one of the most important causes triggering large deformation and failure of soft-rock engineering; however, few studies have paid attention to damage evolution and constitutive relationship of rock in water-weakening process In this paper, laboratory tests are first carried out to estimate the evolution of mechanical properties along with changes of immersion time for shale samples Then with the aid of X-ray diffraction and scanning electron microscope, mechanism of parameter degradation for shale under immersion conditions is investigated from the microscopic perspective Based on the generalized strain equivalent principle and the theory of statistical microscopic damage mechanics, a damage constitutive model of rock subjected to water-weakening effect and uniaxial loading is established by considering the influence of void-compression stage, and the proposed model is verified to be in good agreement with the experiment results This paper provides an effective approach to analyze the constitutive relationship of rock subjected to water-weakening effect and uniaxial loading

Mechanical Behavior and Damage Constitutive Model of Rock Subjected to Water-Weakening Effect and Uniaxial Loading

Evaluation method of rock brittleness based on statistical constitutive relations for rock damage

The calculation method based on the equivalent continuum for the fracture initiation pressure of fracturing of coalbed methane well

https://link.springer.com/content/pdf/10.1007%2Fs12182-018-0252-z.pdf

Experimental investigation of propagation mechanisms and fracture morphology for coalbed methane reservoirs

In developing internal fracture systems in coal beds, the initiation mechanism differs greatly from that of conventional ones and initiations may be produced beyond the wellbore wall. This paper describes the features of the internal structure of coal beds and RFPA2D simulation is used to attest the possible occurrence of initiation beyond the wellbore wall in coal bed hydraulic fracturing. Using the theory of elasticity and fracture mechanics, we analyse the stress distribution in the vicinal coal rock. Then by taking into consideration the effects of the spatial relationship between coal bed cleats and the wellbore, we establish a model for calculating both tensile and shear initiation pressure that occur along cleats beyond the wellbore wall. The simulation in this paper indicates that for shear initiations that happen along coal cleats, the pressure required to initiate fracture for cleats beyond the wellbore wall is evidently lower than that on the wellbore wall, thus it is easier to initiate shear fractures for cleats beyond the wellbore wall. For tensile failure, the pressure required to initiate tensile fracture for cleats beyond the wellbore wall is obviously higher than that for cleats at the wellbore wall, thus it is easier to initiate tensile fractures for cleats at the wellbore wall. On the one hand, this paper has proved the possible occurrence of initiations beyond the wellbore wall and has changed the current assumption that hydraulic fractures can only occur at the wellbore wall. On the other hand, the established theoretical model provides a new approach to calculating the initiation pressure in hydraulic fracturing.

http://iopscience.iop.org/article/10.1088/1742-2132/13/4/536/pdf

Hydraulic fracturing model featuring initiation beyond the wellbore wall for directional well in coal bed

https://onlinelibrary.wiley.com/doi/epdf/10.1002/ese3.567

Dan Jia

Papers

Evaluation method of rock brittleness based on statistical constitutive relations for rock damage

The calculation method based on the equivalent continuum for the fracture initiation pressure of fracturing of coalbed methane well

Experimental investigation of propagation mechanisms and fracture morphology for coalbed methane reservoirs

Hydraulic fracturing model featuring initiation beyond the wellbore wall for directional well in coal bed

Rock damage evolution model of pulsating fracturing based on energy evolution theory