The deliverability evaluation of abnormal high pressure gas reservoir with stress sensitivity model

Stress-sensitive permeability (SSP) influences gas well productivity and is a crucial element influencing gas reservoir development. SSP for high-pressure fractured gas reservoirs with an initial reservoir pressure of more than 20 MPa has never been comprehensively evaluated to the best of our knowledge. SSP experiments with special procedures were designed by adopting the variable confining pressure (VCP) and variable internal pressure (VIP) methods. VCP is a test method in which confining pressure is altered and a constant internal pressure is maintained for the experimental core holder. VIP is a test method in which internal pressure is changed and a constant confining pressure is maintained. A four-stage curve analysis method was developed to perform regressions on semi-logarithmic curves and exponential curves of experimental data. A method to evaluate the SSP was presented using stress sensitivity coefficients obtained via regressions. A calculation approach for determining the degrees of permeability damage and permeability recovery was also proposed. Six matrix cores and six cores with artificial fractures from a high-pressure fractured sandstone gas reservoir were tested using the two methods. The SSP curves for high-pressure reservoirs were characterized by four-stage variation trends, which differentiated with low-pressure reservoirs with an initial reservoir pressure less than 20 MPa. The stress sensitivity of the VCP method was stronger than that of the VIP method. The core samples mainly showed a “Medium” / “Medium-Strong” stress sensitivity under low/high effective stress conditions. Compared with matrix cores, fractured cores showed stronger stress sensitivity owing to its strong plasticity and weak elasticity. The maximum permeability damage degree reached 99.67% and the minimum permeability recovery was only 6.9%. The presented method of experimental design, four-stage curve analysis, stress sensitivity evaluation and the summarized findings in this paper can provide references for future studies on SSP in high-pressure fractured sandstone gas reservoirs.

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An Experimental Study on Percolation Characteristics of a Single-Phase Gas in a Low-Permeability Volcanic Reservoir Under High Pressure

The Open Petroleum Engineering Journal ◽

10.2174/1874834101508010186 ◽

2015 ◽

Vol 8 (1) ◽

pp. 186-192

Author(s):

Tang Xiaoyan

Keyword(s):

High Pressure ◽

Pore Pressure ◽

Gas Flow ◽

Single Phase ◽

Stress Sensitivity ◽

Gas Production ◽

Low Permeability ◽

Gas Reservoir ◽

The Core ◽

Slippage Effect

In this paper, we find that with the decrease in the average pore pressure in the process of gas production, both the slippage effect and the stress sensitivity effect will gradually increase; the increase in the slippage effect is significant, while the increase in the stress sensitivity effect is not. In this paper, the Kalamay volcanic gas reservoir of the Junggar Basin in China was selected as the object of our research. The gas reservoir has typical fractured volcanic reservoirs, and the long-term percolation feature remains unclear. To study the percolation characteristics of singlephase gas under high pressure, the experimental method was designed to simulate these characteristics in the process of gas production by measuring the gas flow in the core and the input and the output pressure at both ends. We carried out simulation experiments of single-phase gas flow percolation characteristics under high pressure using 11 pieces of volcanic rock samples in three wells of the study area. The results show that as the core pore pressure increased, the permeability of low-permeability cores of the volcanic rock decreased significantly at room temperature. However, this decrease became more gradual, which means that the higher the core pore pressure is, the smaller the permeability variation caused by gas slippage is; when the pore pressure is above 10 MPa, the permeability is nearly constant, slippage effect significantly reduces in the process of gas percolation, so it can be completely ignored under these formation conditions. As the pore pressure decreases, the slippage effect and stress sensitivity effect will gradually increase; when the pore pressure is less than 10 MPa, the permeability appears to increase significantly, and this is especially true for a pressure of 5 MPa. The main cause of this result is the slippage effect of gas seepage during the depletion of the gas reservoir, when the pore pressure is lower than a certain value. The valid stress changes of the core are not large, and the stress sensitivity is not strong, so the slippage effect plays a major role, which leads to an increase in the gas permeability during the late period of certain flow gas production.

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Experiment on Mechanical Properties and Seepage Capability of Deep Tight Sandstone Under True-Triaxial Stresses Environment

10.2118/208082-ms ◽

2021 ◽

Author(s):

Jiaying Li ◽

Chunyan Qi ◽

Ye Gu ◽

Yu Ye ◽

Jie Zhao

Keyword(s):

Mechanical Properties ◽

In Situ Stress ◽

Stress Sensitivity ◽

Stress Conditions ◽

Tight Sandstone ◽

Gas Reservoir ◽

True Triaxial ◽

Strain Behavior ◽

Triaxial Stresses

Abstract The characteristics of seepage capability and rock strain during reservoir depletion are important for reservoir recovery, which would significantly influence production strategy optimization. The Cretaceous deep natural gas reservoirs in Keshen Gasfield in Tarim Basin are mainly buried over 5000 m, featuring with ultra-low permeability, developed natural fractures and complex in-situ stress states. However, there is no comprehensive study on the variation of mechanical properties and seepage capability of this gas reservoir under in-situ stress conditions and most studies on stress-sensitivity are conducted under conventional triaxial or uniaxial stress conditions, which cannot truly represent in-situ stress environment. In this work, Cretaceous tight sandstone in Keshen Gasfield was tested under true-triaxial stresses conditions by an advanced geophysical imaging true-triaxial testing system to study the stress-sensitivity and anisotropy of rock stress-strain behavior, porosity and permeability. Four groups of sandstone samples are prepared as the size of 80mm×80mm×80mm, three of which are artificially fractured with different angle (0°,15°，30°) to simulate hydraulic fracturing. The test results corresponding to different samples are compared to further reveal the influence of the fracture angle on rock mechanical properties and seepage capability. The samples are in elastic strain during reservoir depletion, showing an apparent correlation with fracture angles. The porosity decreases linearly with stress loading, where the decrease rate of effective porosity of fracture samples is significantly higher than that of intact samples. The permeabilities decrease exponentially and show significant anisotropy in different principal stress directions, especially in σH direction. The mechanical properties and seepage capability of deep tight sandstone are successfully tested under true-triaxial stresses conditions in this work, which reveals the stress-sensitivity of anisotropic permeability, porosity and stress-strain behavior during gas production. The testing results proposed in this paper provides an innovative method to analyse rock mechanical and petrophysical properties and has profound significance on exploration and development of tight gas reservoir.

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Application and Study of Fine-Silty Sand Control Technique Using Fiber-Complex High-Pressure Pack in Sebei Gas Reservoir

10.2118/97832-ms ◽

2006 ◽

Cited By ~ 1

Author(s):

Fujian Zhou ◽

Yiping Zong ◽

Yuzhang Liu ◽

Xianyou Yang ◽

Chunming Xiong ◽

...

Keyword(s):

High Pressure ◽

Silty Sand ◽

Control Technique ◽

Gas Reservoir ◽

Sand Control

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Productivity Influence Factors of Tight Sandstone Gas Reservoir with Water Produced

Geofluids ◽

10.1155/2021/9926299 ◽

2021 ◽

Vol 2021 ◽

pp. 1-9

Author(s):

Yongchao Xue ◽

Qingshuang Jin ◽

Hua Tian

Keyword(s):

Pressure Gradient ◽

Relative Permeability ◽

Gas Flow ◽

Influence Factors ◽

Stress Sensitivity ◽

Consumption Pattern ◽

Tight Sandstone ◽

Gas Reservoir ◽

Two Phase ◽

Start Up

Finding ways to accelerate the effective development of tight sandstone gas reservoirs holds great strategic importance in regard to the improvement of consumption pattern of world energy. The pores and throats of the tight sandstone gas reservoir are small with abundant interstitial materials. Moreover, the mechanism of gas flow is highly complex. This paper is based on the research of a typical tight sandstone gas reservoir in Changqing Oilfield. A strong stress sensitivity in tight sandstone gas reservoir is indicated by the results, and it would be strengthened with the water production; at the same time, a rise to start-up pressure gradient would be given by the water producing process. With the increase in driving pressure gradient, the relative permeability of water also increases gradually, while that of gas decreases instead. Following these results, a model of gas-water two-phase flow has been built, keeping stress sensitivity, start-up pressure gradient, and the change of relative permeability in consideration. It is illustrated by the results of calculations that there is a reduction in the duration of plateau production period and the gas recovery factor during this period if the stress sensitivity and start-up pressure gradient are considered. In contrast to the start-up pressure gradient, stress sensitivity holds a greater influence on gas well productivity.

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Stress Sensitivity of Low Permeable and Water-Bearing Gas Reservoir without Gas Slippage Effect

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.962-965.570 ◽

2014 ◽

Vol 962-965 ◽

pp. 570-573

Author(s):

Jian Yan ◽

Xiao Bing Liang ◽

Qian Wu ◽

Qing Guo

Keyword(s):

Water Saturation ◽

Stress Sensitivity ◽

Testing Methods ◽

Gas Reservoirs ◽

Gas Reservoir ◽

Gas Well ◽

Well Production ◽

Gas Slippage ◽

Slippage Effect ◽

Function Relationship

Because of the gas slippage, the testing methods of stress sensitivity for gas reservoir should be different from that for oil reservoir. This text adopts the method that imposing back pressure on the outlet of testing core to weaken the gas slippage effect and tests the stress sensitivity of low permeability gas reservoirs, then analyzes the influence of permeability and water saturation on stress sensitivity. The results show that: low permeable and water-bearing gas reservoirs have strong stress sensitivity; the testing permeability has the power function relationship with net stress, compared to the exponential function, the fitting correlation coefficient is larger and more suited to the actual; the lower the permeability is and the higher water saturation is, the stronger the stress sensitivity is. The production of gas well is affected when considering the stress sensitivity, so the pressure dropping rate should be reasonable when low permeable gas reservoirs are developed. The results provide theoretical references for analyzing the well production and numerical simulation.

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