Methodology for predicting reservoir breakdown pressure and fracture opening pressure in low-permeability reservoirs based on an in situ stress simulation

The complexity of hydraulic fractures (HF) significantly affects the success of reservoir reconstruction. The existence of a bedding plane (BP) in shale impacts the extension of a fracture. For shale reservoirs, in order to investigate the interaction mechanisms of HF and BPs under the action of coupled stress-flow, we simulate the processes of hydraulic fracturing under different conditions, such as the stress difference, permeability coefficients, BP angles, BP spacing, and BP mechanical properties using the rock failure process analysis code (RFPA2D-Flow). Simulation results showed that HF spread outward around the borehole, while the permeability coefficient is uniformly distributed at the model without a BP or stress difference. The HF of the formation without a BP presented a pinnate distribution pattern, and the main direction of the extension is affected by both the ground stress and the permeability coefficient. When there is no stress difference in the model, the fracture extends along the direction of the larger permeability coefficient. In this study, the in situ stress has a greater influence on the extension direction of the main fracture when using the model with stress differences of 6 MPa. As the BP angle increases, the propagation of fractures gradually deviates from the BP direction. The initiation pressure and total breakdown pressure of the models at low permeability coefficients are higher than those under high permeability coefficients. In addition, the initiation pressure and total breakdown pressure of the models are also different. The larger the BP spacing, the higher the compressive strength of the BP, and a larger reduction ratio (the ratio of the strength parameters of the BP to the strength parameters of the matrix) leads to a smaller impact of the BP on fracture initiation and propagation. The elastic modulus has no effect on the failure mode of the model. When HF make contact with the BP, they tend to extend along the BP. Under the same in situ stress condition, the presence of a BP makes the morphology of HF more complex during the process of propagation, which makes it easier to achieve the purpose of stimulated reservoir volume (SRV) fracturing and increased production.

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Research on Stress Sensitivity of Low Permeability Sand Stone Reservoir

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.317-319.2432 ◽

2011 ◽

Vol 317-319 ◽

pp. 2432-2435

Author(s):

Yu Xue Sun ◽

Fei Yao ◽

Jing Yuan Zhao

Keyword(s):

Plastic Deformation ◽

In Situ Stress ◽

Stress Sensitivity ◽

Oil Field ◽

Low Permeability ◽

High Permeability ◽

Permeability Changes ◽

Loading And Unloading ◽

Sandstone Reservoir

In the process of low-permeability sandstone reservoir exploitation, stress sensitivity takes place with the effective stress rises gradually, which will cause permeability decline. Allowing to the condition of in-situ stress, the study and experiment on the rock core in Jilin oil field Fuxin326 oil layer are presented. The experimental results show that the stress sensitivity of this oil layer is small; the regularity of permeability changes is in accordance with exponential function. The stress sensitivity of high permeability core is larger than that of low permeability core. Moreover, experimental and theoretical analysis shows that low permeability core has a larger permeability loss than high permeability core in loading and unloading process where elastic plastic deformation of rock will happen, which is the major reason that permeability loss can not return completely.

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Study on the Coalbed Methane Development under High In Situ Stress, Large Buried Depth, and Low Permeability Reservoir in the Libi Block, Qinshui Basin, China

Advances in Civil Engineering ◽

10.1155/2020/6663496 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13

Author(s):

Jinkuang Huang ◽

Shenggui Liu ◽

Songlei Tang ◽

Shixiong Shi ◽

Chao Wang

Keyword(s):

Coalbed Methane ◽

Horizontal Wells ◽

In Situ Stress ◽

Low Permeability ◽

Qinshui Basin ◽

Hole Pressure ◽

Bottom Hole ◽

Single Well ◽

Coal Reservoir

Coalbed methane (CBM) has been exploited in the deep area of the coal reservoir (>1000 m). The production of CBM vertical wells is low because of the high in situ stress, large buried depth, and low permeability of the coal reservoir. In this paper, efficient and advanced CBM development technology has been applied in the Libi Block of the Qinshui Basin. According to the characteristics of the coal reservoir in the Libi Block, the coiled tubing fracturing technology has been implemented in four cluster horizontal wells. Staged fracturing of horizontal wells can link more natural fracture networks. It could also expand the pressure drop range and control area of the single well. This fracturing technology has achieved good economic results in the Libi Block, with the maximum production of a single horizontal well being 25313 m3/d and the average single well production having increased by more than 60% from 5000 m3/d to 8000 m3/d. Based on the data regarding the bottom hole pressure, water production, and gas production, the production curves of four wells, namely, Z5P-01L, Z5P-02L, Z5P-03L, and Z5P-04L, were investigated. Furthermore, a production system with slow and stable depressurization was obtained. The bottom hole pressure drops too fast, which results in decreasing permeability and productivity. In this work, a special jet pump and an intelligent remote production control system for the CBM wells were developed; hence, a CBM production technology suitable for the Libi Block was established. The maximum release for the CBM well productivity was obtained, thus providing theoretical and technical support for CBM development with geological and engineering challenges.

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Numerical Investigation of the Impacts of Borehole Breakouts on Breakdown Pressure

Energies ◽

10.3390/en12050888 ◽

2019 ◽

Vol 12 (5) ◽

pp. 888 ◽

Cited By ~ 3

Author(s):

Hua Zhang ◽

Shunde Yin ◽

Bernt Aadnoy

Keyword(s):

Hydraulic Fracturing ◽

Shear Failure ◽

In Situ Stress ◽

Test Results ◽

Breakdown Pressure ◽

Borehole Breakout ◽

Borehole Breakouts ◽

The Difference ◽

Mud Pressure

Borehole breakouts appear in drilling and production operations when rock subjected to in situ stress experiences shear failure. However, if a borehole breakout occurs, the boundary of the borehole is no longer circular and the stress distribution around it is different. So, the interpretation of the hydraulic fracturing test results based on the Kirsch solution may not be valid. Therefore, it is important to investigate the factors that may affect the correct interpretation of the breakdown pressure in a hydraulic fracturing test for a borehole that had breakouts. In this paper, two steps are taken to implement this investigation. First, sets of finite element modeling provide sets of data on borehole breakout measures. Second, for a given measure of borehole breakouts, according to the linear relation between the mud pressure and the stress on the borehole wall, the breakdown pressure considering the borehole breakouts is acquired by applying different mud pressure in the model. Results show the difference between the breakdown pressure of a circular borehole and that of borehole that had breakouts could be as large as 82% in some situations.

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Numerical Investigation of Injection-Induced Fracture Propagation in Brittle Rocks with Two Injection Wells by a Modified Fluid-Mechanical Coupling Model

Energies ◽

10.3390/en13184718 ◽

2020 ◽

Vol 13 (18) ◽

pp. 4718

Author(s):

Song Wang ◽

Jian Zhou ◽

Luqing Zhang ◽

Zhenhua Han

Keyword(s):

Fracture Propagation ◽

In Situ Stress ◽

Hydraulic Fractures ◽

Fracture Networks ◽

Breakdown Pressure ◽

Injection Wells ◽

Mechanical Coupling ◽

Stress Shadow ◽

Well Spacing

Hydraulic fracturing is a key technical means for stimulating tight and low permeability reservoirs to improve the production, which is widely employed in the development of unconventional energy resources, including shale gas, shale oil, gas hydrate, and dry hot rock. Although significant progress has been made in the simulation of fracturing a single well using two-dimensional Particle Flow Code (PFC2D), the understanding of the multi-well hydraulic fracturing characteristics is still limited. Exploring the mechanisms of fluid-driven fracture initiation, propagation and interaction under multi-well fracturing conditions is of great theoretical significance for creating complex fracture networks in the reservoir. In this study, a series of two-well fracturing simulations by a modified fluid-mechanical coupling algorithm were conducted to systematically investigate the effects of injection sequence and well spacing on breakdown pressure, fracture propagation and stress shadow. The results show that both injection sequence and well spacing make little difference on breakdown pressure but have huge impacts on fracture propagation pressure. Especially under hydrostatic pressure conditions, simultaneous injection and small well spacing increase the pore pressure between two injection wells and reduce the effective stress of rock to achieve lower fracture propagation pressure. The injection sequence can change the propagation direction of hydraulic fractures. When the in-situ stress is hydrostatic pressure, simultaneous injection compels the fractures to deflect and tend to propagate horizontally, which promotes the formation of complex fracture networks between two injection wells. When the maximum in-situ stress is in the horizontal direction, asynchronous injection is more conducive to the parallel propagation of multiple hydraulic fractures. Nevertheless, excessively small or large well spacing reduces the number of fracture branches in fracture networks. In addition, the stress shadow effect is found to be sensitive to both injection sequence and well spacing.

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Micromechanical Model for Simulating Hydraulic Fractures of Rock

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.9.127 ◽

2005 ◽

Vol 9 ◽

pp. 127-136 ◽

Cited By ~ 1

Author(s):

Tian Hong Yang ◽

Leslie George Tham ◽

S.Y. Wang ◽

Wan Cheng Zhu ◽

Lian Chong Li ◽

...

Keyword(s):

Numerical Model ◽

Stress Ratio ◽

Failure Process ◽

Micromechanical Model ◽

In Situ Stress ◽

Hydraulic Fractures ◽

Breakdown Pressure ◽

Heterogeneous Rocks ◽

Material Homogeneity

A numerical model is developed to study hydraulic fracturing in permeable and heterogeneous rocks, coupling with the flow and failure process. The effects of flow and in-situ stress ratio on fracture, material homogeneity and breakdown pressure are specifically studied.

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