scholarly journals A Case Study on the Optimal Design of the Horizontal Wellbore Trajectory for Hydraulic Fracturing in Nong’an Oil Shale

Energies ◽  
2020 ◽  
Vol 13 (1) ◽  
pp. 286
Author(s):  
Ying Zhu ◽  
Han Zhang ◽  
Dongbin Pan ◽  
Lianghao Zhai ◽  
Shuai Gao ◽  
...  
Keyword(s):  
Oil Shale ◽  
Fracture Initiation ◽  
Intact Rock ◽  
Hydraulic Fractures ◽  
Trajectory Design ◽  
Rock Matrix ◽  
Preferred Direction ◽  
Bedding Planes ◽  
Horizontal Wellbore

A horizontal well with hydraulic fractures is key to forming a fracture network in oil shale for the generated hydrocarbon flows. By considering the influence of anisotropic strength, a prediction model is proposed for fracture initiation by studying different fracture initiation modes (FIMs) in oil shale: failure of the intact rock matrix and of the bedding planes. Through a case study on Nong’an oil shale, the influences of wellbore trajectory and bedding planes on the fracture initiation pressure (FIP), location (FIL), and FIM were analyzed and the induced changes in wellbore trajectory design were concluded. The preferred angle between the wellbore axis and the minimum horizontal principal stress was the same of 90° or 270°, when the lowest required FIP corresponded to the failure of the intact rock matrix. However, when the angle corresponded to the failure of the bedding planes, the preferred direction of the wellbore axis was away from the fixed direction and not corresponding to the lowest required FIP due to the fracture morphology. The error between the theoretical and experimental results ranges from 7% to 9%. This research provides a framework for the design of horizontal wellbore trajectories in oil shale, for easier fracture initiation and more complex fracture networks.

Karst massif susceptibility from rock matrix, fracture and conduit porosities: a case study of the Sierra de las Nieves (Málaga, Spain)

2015 ◽  
Vol 74 (12) ◽  
pp. 7583-7592 ◽  
Author(s):  
Eulogio Pardo-Igúzquiza ◽  
Juan José Durán ◽  
Juan A. Luque-Espinar ◽  
Pedro A. Robledo-Ardila ◽  
Sergio Martos-Rosillo ◽  
...  
Keyword(s):  
Rock Matrix ◽  
Matrix Fracture

Near-Wellbore Hydraulic Fracture Non-Planar Propagation and Torturous Morphology in Tight Sandstone Formation

2021 ◽  
Author(s):  
Ruxin Zhang ◽  
Qinglin Shan ◽  
Wan Cheng
Keyword(s):  
Stress Distribution ◽  
Fracture Initiation ◽  
Damage Mechanism ◽  
Fracture Morphology ◽  
Propagation Model ◽  
Hydraulic Fractures ◽  
Tight Sandstone ◽  
Propagation Behavior ◽  
Stress Shadow ◽  
Sandstone Formation

Abstract In this paper, a 3D near-wellbore fracture propagation model is established, integrating five parts: formation stress balance, drilling, casing and cementing, perforating, and fracturing, in order to investigate fracture initiation characteristics, near-wellbore fracture non-planar propagation behavior, and torturous hydraulic fracture morphology for cased and perforated horizontal wellbores in tight sandstone formation. The method is based on the combination of finite element method and post-failure damage mechanism. Finite element method is used to determine the coupling behavior between the pore fluid seepage and rock stress distribution. Post-failure damage mechanism is adopted to test the evolution of hydraulic fractures through simulating rock damage process. Moreover, a user subroutine is introduced to establish the relation between rock strength, permeability, and damage, in order to solve the model. This model could simulate the interaction between fractures during their propagation process because of the stress shadow. The simulation results indicate that each operation could cause redistribution and reorientation of near-wellbore stress. Therefore, it is important to know the real near-wellbore stress distribution that affects near-wellbore fracture initiation and propagation. Initially, hydraulic fractures initiate independently from each perforation and propagate along the direction of maximum horizontal stress. However, hydraulic fractures divert from original direction gradually to interconnect and overlap with each other, because of stress shadow, resulting in non-planar propagation behavior. Individual fractures coalesce into a spiral-shaped fracture morphology. In addition, a longitudinal fracture could be observed because of wellbore effect, which is a result of weak cementing strength or near-wellbore weak plane. Finally, the complex and torturous fracture morphologies are created near the wellbore, incorporating Multi-spiral shaped fracture and horizontal-vertical crossing shaped fracture. However, the propagation behavior of fracture far away from wellbore is controlled by in-situ stress, forming a planar fracture. The highlights of this 3D near-wellbore fracture propagation model are following: 1) it considers near-wellbore stress change caused by each construction to ensure the accuracy of near-wellbore stress distribution; 2) it achieves 3D simulation of fracture initiation and near-wellbore propagation from perforations; 3) the interaction between fractures is involved, resulting in complex and torturous morphology. This model provides the theoretical basis for fracture initiation and propagation, which also could be applied into heterogenous formations considering the effect of discontinuities.

An improved hazard assessment chart for rock falls in near vertical blocky rock environments

2021 ◽  
Author(s):  
Fhatuwani Sengani ◽  
Mulenga Francois
Keyword(s):  
Slope Angle ◽  
Vegetation Density ◽  
Rock Falls ◽  
Structural Mapping ◽  
Initial Height ◽  
Rockfall Hazard ◽  
Final Destination ◽  
Bedding Planes ◽  
Hazard Rating

Abstract The purpose of the study was to perform rockfall stability analysis and develop an improved rockfall hazard matrix chart using the R518 road in Limpopo as the case study. The study entailed structural mapping, wedge simulation using stereonet plots. The RocFall software was then used to identify the parameters that influence the occurrence of rockfall. The software was also used to monitor the variations in the kinetic energy of rolling, bouncing or falling rocks. The effects of the initial height and velocity of falling rocks on the final destination of fragments were also explored. Results showed that the selected area along the R518 road consists of joints and bedding planes. These features weaken the rock mass and create wedges that can potentially fall. Simulations with RocFall, on the other hand, indicated that slope height, vegetation density, slope angle, the velocity of the falling rock largely contribute to the extent that the broken rock could reach. From the empirical and numerical findings, an improved rockfall hazard rating chart was proposed. The chart was found to be suitable for the rating of level of rockfall hazard along highways and roads.

Fracture Prevention Following Offshore Well Blowouts: Selecting the Appropriate Capping Stack Shut-In Strategy

2020 ◽  
pp. 1-13
Author(s):  
Andreas Michael ◽  
Ipsita Gupta
Keyword(s):  
Fracture Initiation ◽  
Loss Of Control ◽  
Flow Rates ◽  
Discharge Flow ◽  
Well Control ◽  
Wellbore Integrity ◽  
Discharge Flow Rate ◽  
Critical Discharge ◽  
Control Situations

Summary Following uncontrolled discharge during loss of well control events, fracture initiation occurring during the post-blowout capping stage can lead to reservoir fluids broaching to the seafloor. A classic example is Union Oil's 1969 oil spill in Santa Barbara Channel, where fracture initiation at various locations caused thousands of gallons per hour to broach onto the ocean floor over a month before it could be controlled (Mullineaux 1970; Easton 1972). Disasters such as these could be prevented if the effects of the post-blowout loss of well control stages (uncontrolled discharge and capping) are incorporated into the shut-in procedures, and the wellbore architectures are modified accordingly. In this study, analytical models are used to simulate the loads on the wellbore during the different stages of loss of control. Capping pressure buildup during the shut-in is modeled to indicate fracture initiation points during the capping stage. Using these models, the critical capping pressure for a well is determined, and subsequent critical discharge flow rates are calculated. Fracture initiation would occur if the actual discharge flow rate is below the calculated critical discharge flow rate. A hypothetical case study using typical deepwater Gulf of Mexico (GOM) parameters is performed demonstrating the likelihood of fracture initiation during different discharge flow rates, discharge periods, and capping stack shut-in methods (single-step/“abrupt” or multistep/“incremental”). An abrupt shut-in for this case study leads to fracture initiation at approximately 8 hours after shut-in, while a five-step incremental shut-in is shown to prevent any fracture initiation during the 48 hours after the beginning of the shut-in. Reservoir depletion through longer discharge periods or higher discharge flow rates, despite the adverse environmental effect, can delay or even prevent fracture initiations during post-blowoutcapping. The ability to model these fracture failures enhances the understanding of wellbore integrity problems induced during loss of control situations and helps create workflows for predicting possible broaching scenarios during the post-blowout capping stage. Dimensionless plots are used to present fracture initiation for different cases—this is useful for drilling and wellbore integrity engineers for making contingency plans for dealing with loss of well control situations.

Effect of pyrolysis on oil shale using superheated steam: A case study on the Fushun oil shale, China

Fuel ◽  
2019 ◽  
Vol 253 ◽  
pp. 1490-1498 ◽  
Author(s):  
Lei Wang ◽  
Yangsheng Zhao ◽  
Dong Yang ◽  
Zhiqin Kang ◽  
Jing Zhao
Keyword(s):  
Oil Shale ◽  
Superheated Steam
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