scholarly journals A New Method for Research on Unsteady Pressure Dynamics and Productivity of Ultralow-Permeability Reservoirs

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Kun Wang ◽  
Li Li ◽  
Xiao Chen ◽  
Wei Liang ◽  
Yong Yang ◽  
...  
Keyword(s):  
Stress Sensitivity ◽  
Low Permeability ◽  
Threshold Pressure ◽  
Test Interpretation ◽  
Well Test ◽  
Pressure Derivative ◽  
Threshold Pressure Gradient ◽  
The Real ◽  
Skin Factor ◽  
Low Permeability Reservoirs

In the numerous low-permeability reservoirs, knowing the real productivity of the reservoir became one of the most important steps in its exploitation. However, the value of permeability interpreted by a conventional well-test method is far lower than logging, which further leads to an inaccurate skin factor. This skin factor cannot match the real production situation and will mislead engineer to do an inappropriate development strategy of the oilfield. In order to solve this problem, key parameters affecting the skin factor need to be found. Based on the real core experiment and digital core experiment results, stress sensitivity and threshold pressure gradient are verified to be the most influential factors in the production of low-permeability reservoirs. On that basis, instead of a constant skin factor, a well-test interpretation mathematical model is established by defining and using a time-varying skin factor. The time-varying skin factor changes with the change of stress sensitivity and threshold pressure gradient. In this model, the Laplace transform is used to solve the Laplace space solution, and the Stehfest numerical inversion is used to calculate the real space solution. Then, the double logarithmic chart of dimensionless borehole wall pressure and pressure derivative changing with dimensionless time is drawn. The influences of parameters in expressions including stress sensitivity, threshold pressure, and variable skin factor on pressure and pressure derivative and productivity are analyzed, respectively. At last, the method is applied to the well-test interpretation of low-permeability oil fields in the eastern South China Sea. The interpretation results turn out to be reasonable and can truly reflect the situation of low-permeability reservoirs, which can give guidance to the rational development of low-permeability reservoirs.

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.

Numerical Well-Testing Model of Fractured-Well in Low Permeability Reservoir Based on Mutative Permeability Effect

2013 ◽  
Vol 433-435 ◽  
pp. 1984-1987
Author(s):  
Yu Chen Zhang ◽  
Jiu Ning Zhou ◽  
Jing Wen Cui
Keyword(s):  
Low Permeability ◽  
Well Testing ◽  
Upward Movement ◽  
Threshold Pressure ◽  
Algebraic Equations ◽  
Pressure Derivative ◽  
Threshold Pressure Gradient ◽  
Well Model ◽  
Numerical Well Testing ◽  
Fractured Well

At present, threshold pressure gradient method is usually used for describing fluid flow in low-permeability media. However, it is only an approximate approach. In this paper, a 2-D fractured-well model for numerical well-testing considering non-darcy mutative-permeability effect was established, and PSOR iterative algorithm was used for solving the sets of algebraic equations. Based on this model, the typical curves of pressure and pressure derivative were drawn with different sets of parameters. When considering mutative-permeability effect, the pressure derivative curves move upward in each flowing period compared with darcy flowing model. In addition, the range of upward movement is larger as the non-darcy effect is more notable.

scholarly journals Nonlinear Flow Characteristics and Horizontal Well Pressure Transient Analysis for Low-Permeability Offshore Reservoirs

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Jianchun Xu ◽  
Ruizhong Jiang ◽  
Wenchao Teng
Keyword(s):  
Horizontal Well ◽  
Flow Characteristics ◽  
Stress Sensitivity ◽  
Nonlinear Flow ◽  
Absolute Permeability ◽  
Low Permeability ◽  
Threshold Pressure Gradient ◽  
Pressure Transient ◽  
Permeability Modulus ◽  
Low Permeability Reservoirs

Threshold pressure gradient (TPG) and stress sensitivity which cause the nonlinear flow in low permeability reservoirs were carried out by experiments. Firstly, the investigation of existing conditions of TPG for oil flow in irreducible water saturation low-permeability reservoirs was conducted and discussed, using the cores from a real offshore oilfield in China. The existence of TPG was proven. The relationship between TPG and absolute permeability was obtained by laboratory tests. TPG increases with decreasing absolute permeability. Then, stress sensitivity experiment was carried out through depressurizing experiment and step-up pressure experiment. Permeability modulus which characterizes stress sensitivity increases with decreasing absolute permeability. Consequently, a horizontal well pressure transient analysis mathematical model considering threshold pressure gradient and stress sensitivity was established on the basis of mass and momentum conservation equations. The finite element method (FEM) was presented to solve the model. Influencing factors, such as TPG, permeability modulus, skin factor, wellbore storage, horizontal length, horizontal position, and boundary effect on pressure and pressure derivative curves, were also discussed. Results analysis demonstrates that the pressure transient curves are different from Darcy’s model when considering the nonlinear flow characteristics. Both TPG and permeability modulus lead to more energy consumption and the reservoir pressure decreases more than Darcy’s model.

Threshold Pressure Gradient in Ultra-low Permeability Reservoirs

2008 ◽  
Vol 26 (9) ◽  
pp. 1024-1035 ◽  
Author(s):  
F. Hao ◽  
L. S. Cheng ◽  
O. Hassan ◽  
J. Hou ◽  
C. Z. Liu ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Low Permeability ◽  
Threshold Pressure ◽  
Threshold Pressure Gradient ◽  
Low Permeability Reservoirs

scholarly journals Pressure Performance of Highly Deviated Well in Low Permeability Carbonate Gas Reservoir Using a Composite Model

Energies ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5952
Author(s):  
Qinwen Zhang ◽  
Liehui Zhang ◽  
Qiguo Liu ◽  
Youshi Jiang
Keyword(s):  
Pressure Gradient ◽  
Stress Sensitivity ◽  
Composite Model ◽  
Darcy Flow ◽  
Low Permeability ◽  
Threshold Pressure ◽  
Gas Reservoir ◽  
Threshold Pressure Gradient ◽  
Effects Of Stress ◽  
Deviated Wells

It is commonly believed that matrix and natural fractures randomly distribute in carbonate gas reservoirs. In order to increase the effective connected area to the storage space as much as possible, highly deviated wells are widely used for development. Although there have been some studies on the composite model for highly deviated wells, they have not considered the effects of stress sensitivity and threshold pressure gradient in a dual-porosity gas reservoir. In this paper, a semi-analytical composite model for low permeability carbonate gas reservoir was established to study the effect of non-Darcy flow. By employing source function, Fourier transform and the perturbation method, the pressure performance and typical well test curves were obtained. Eight flow regimes were identified, and their characteristics were discussed. As a result, it can be concluded that the effects of stress sensitivity and threshold pressure gradient would make pseudo-pressure and derivative curves rise, which is the characteristic of non-Darcy flow to determine whether there is stress sensitivity or threshold pressure gradient.

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