scholarly journals Stress sensitivity of tight reservoirs during pressure loading and unloading process

2019 ◽  
Vol 46 (1) ◽  
pp. 138-144 ◽  
Author(s):  
Nai CAO ◽  
Gang LEI
Keyword(s):  
Stress Sensitivity ◽  
Pressure Loading ◽  
Tight Reservoirs ◽  
Loading And Unloading

scholarly journals Stress-Dependent Permeability of Fractures in Tight Reservoirs

Energies ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 117 ◽  
Author(s):  
Nai Cao ◽  
Gang Lei ◽  
Pingchuan Dong ◽  
Hong Li ◽  
Zisen Wu ◽  
...  
Keyword(s):  
Effective Stress ◽  
Influencing Factor ◽  
Quantitative Model ◽  
Stress Sensitivity ◽  
Gas Production ◽  
Fracture System ◽  
Permeability Model ◽  
Fracture Systems ◽  
Tight Reservoirs ◽  
Stress Dependent

Permeability is one of the key factors involved in the optimization of oil and gas production in fractured porous media. Understanding the loss in permeability influenced by the fracture system due to the increasing effective stress aids to improve recovery in tight reservoirs. Specifically, the impacts on permeability loss caused by different fracture parameters are not yet clearly understood. The principal aim of this paper is to develop a reasonable and meaningful quantitative model that manifests the controls on the permeability of fracture systems with different extents of fracture penetration. The stress-dependent permeability of a fracture system was studied through physical tests and numerical simulation with the finite element method (FEM). In addition, to extend capability beyond the existing model, a theoretical stress-dependent permeability model is proposed with fracture penetration extent as an influencing factor. The results presented include (1) a friendly agreement between the predicted permeability reduction under different stress conditions and the practical experimental data; (2) rock permeability of cores with fractures first reduces dramatically due to the closure of the fractures, then the permeability decreases gradually with the increase in effective stress; and (3) fracture penetration extent is one of the main factors in permeability stress sensitivity. The sensitivity is more influenced by fracture systems with a larger fracture penetration extent, whereas matrix compaction is the leading influencing factor in permeability stress sensitivity for fracture systems with smaller fracture penetration extents.

A Novel Model for Well Production Performance Estimate in Low-Permeability and Tight Reservoirs Considering Stress Sensitivity

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Mingda Dong ◽  
Xuedong Shi ◽  
Jie bai ◽  
Zhilong Yang ◽  
Zhilin Qi
Keyword(s):  
Pressure Gradient ◽  
Effective Stress ◽  
Stress Sensitivity ◽  
Production Performance ◽  
Low Permeability ◽  
Threshold Pressure ◽  
Threshold Pressure Gradient ◽  
Vertical Well ◽  
Tight Reservoirs ◽  
Rock Compressibility

Abstract Stress sensitivity phenomenon is an important property in low-permeability and tight reservoirs and has a large impact on the productivity of production wells, which is defined as the effect of effective stress on the reservoir parameters such as permeability, threshold pressure gradient, and rock compressibility change accordingly. Most of the previous works are focused on the effect of effective stress on permeability and threshold pressure gradient, while rock compressibility is critical of stress sensitivity but rarely noticed. A series of rock compressibility measurement experiments have been conducted, and the quantitative relationship between effective stress and rock compressibility is accurately described in this paper. In the experiment, the defects in previous experiments were eliminated by using a new-type core holder. The results show that as the effective stress increases, the rock compressibility becomes lower. Then, a stress sensitivity model that considers the effect of effective stress on rock compressibility is established due to the experimental results. The well performance of a vertical well estimated by this model shows when considering the effect of effective stress on the rock compressibility, the production rate and recovery factor are larger than those without considering it. Moreover, the effect of porosity and confining pressure on the productivity of a vertical well is also studied and discussed in this paper. The results show that the productivity of a vertical well decreases with the increase in overburden pressure, and increases with the increase in the porosity.

Research on Stress Sensitivity of Low Permeability Sand Stone Reservoir

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.

scholarly journals An Experimental Study on Stress Sensitivity of Tight Sandstones with Different Microfractures

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Xinli Zhao ◽  
Zhengming Yang ◽  
Zhiyuan Wang ◽  
Wei Lin ◽  
Shengchun Xiong ◽  
...  
Keyword(s):  
Gas Permeability ◽  
High Stress ◽  
Confining Pressure ◽  
Fracture Network ◽  
Sensitivity Coefficient ◽  
Stress Sensitivity ◽  
Tight Sandstone ◽  
The Core ◽  
Before And After ◽  
Tight Reservoirs

Aiming at the stress sensitivity problem of tight reservoirs with different microfractures, the cores of H oilfield and J oilfield with different microfractures were obtained through the fractures experiment, so as to study the change of gas permeability in tight sandstone core plug during the change of confining pressure. Besides, we use the nuclear magnetic resonance (NMR) spectra of the core before and after saturation to verify whether the core has been successfully fractured. Based on Terzaghi’s effective stress principle, the permeability damage rate (D) and the stress sensitivity coefficient (Ss) are used to evaluate the stress sensitivity of the core, which show consistency in evaluating the stress sensitivity. At the same time, we have studied the petrological characteristics of tight sandstone in detail using thin section (TS) and scanning electron microscope (SEM). The results show that the existence of microfractures is the main factor for the high stress sensitivity of tight sandstone. In addition, because of the small throat of the tight reservoir core, the throat closes when the overlying stress increases. As a result, the tight sandstone pore size is greatly reduced and the permeability is gradually reduced. Therefore, in the development of tight reservoirs, we should not only consider the complex fracture network produced by fracturing, but also pay attention to the permanent damage of reservoirs caused by stress sensitivity.

scholarly journals Evaluation of the stress sensitivity in tight reservoirs

2016 ◽  
Vol 43 (1) ◽  
pp. 115-123 ◽  
Author(s):  
Wenlian XIAO ◽  
Tao LI ◽  
Min LI ◽  
Jinzhou ZHAO ◽  
Lingli ZHENG ◽  
...  
Keyword(s):  
Stress Sensitivity ◽  
Tight Reservoirs

scholarly journals Investigation of Seepage Law in Broken Coal and Rock Mass under Different Loading and Unloading Cycles

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Zihao Kan ◽  
Lei Zhang ◽  
Mingxue Li ◽  
Xiaochuan Yuan ◽  
Mengqian Huang
Keyword(s):  
Rock Mass ◽  
Loss Rate ◽  
Sensitivity Coefficient ◽  
Stress Sensitivity ◽  
Mining Operations ◽  
Exponential Relationship ◽  
Coal Particles ◽  
Loading And Unloading ◽  
Seepage Law ◽  
The Impact

In order to study the seepage law of broken coal seams affected by multiple mining operations, a cyclic loading and unloading seepage experiment was carried out. For this purpose, the seepage law of broken samples with different coal and rock ratios was analyzed. The results of our study demonstrated that the permeability of the broken samples showed a decreasing trend. After a loading and unloading cycle, the permeability was significantly reduced. The impact of the loading stage on the broken sample was higher than that of the unloading phase. When the proportion of coal particles in the mixed samples of broken coal and rock was 50%, the irreversible permeability loss rate and permeability loss rate of the samples showed the highest values. The irreversible permeability loss rate and permeability loss rate of the broken rock mass were greater than those displayed by the broken coal mass. The stress sensitivity coefficient curves of the 5 types of broken coal and rock masses presented the same changes. The stress sensitivity coefficient curve and the effective stress displayed an exponential relationship.

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