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Abstract

In the development of tight reservoirs, the permeability of the rock possesses strong stress sensitivity with the dynamic change of formation pressure and effective stress. To quantify the stress sensitivity of permeability in tight reservoirs and its impacts on the oil production, we carried out a systematic experimental study using core samples from both tight sandstone and limestone reservoirs in Sichuan Basin. In particular, the stress sensitivity of permeability for each type of rocks was examined at reservoir conditions by two methods: (a) constant pore pressure with variable confining pressure and (b) constant confining pressure with variable pore pressure. The results show that both tight sandstone and limestone reservoirs have strong stress sensitivity of permeability, while the stress sensitivity of permeability for sandstone reservoir is larger than limestone reservoir. In addition, it is found that the variable pore pressure method can better reflect the characteristics of the stress sensitivity of permeability during the development of tight reservoirs than variable confining pressure method. The stress sensitivity of permeability for tight sandstone can be attributed to the impacts of narrow throats, while the stress sensitivity of permeability for tight limestone is dominantly influenced by the micro- and nanoscale fractures. For tight reservoirs with high stress sensitivity, the producing pressure drop can be controlled by selecting a reasonable producing pressure drop to reduce the damage in permeability caused by the stress sensitivity.

Keywords

Tight oil reservoir tight sandstone tight limestone stress sensitivity of permeability reservoir development

Introduction

In recent years, the development of tight oil reservoirs has aroused great interest in petroleum industry (Rashid et al., 2017; Wang et al., 2014a, 2015, 2017). In general, most of the tight reservoirs are exploited by natural energy; therefore, the reservoir rock is in equilibrium state due to a combined action of overburden pressure, pore fluid pressure and matrix stress. However, with the exploitation of the reservoir, the pore fluid pressure decreases, resulting in a gradual increase in the effective stress of the rock matrix and thereby a gradual change in the pore structure and volume. This variation of rock matrix with effective stress is the so-called stress sensitivity, which is also known as pressure sensitivity. The change in pore structure and volume on the other hand will significantly affect the porosity and permeability of the reservoir, and ultimately, it will affect the fluid flow and the production performance of the reservoir (Liu et al., 2017). Especially, a large number of studies have proved that the stress sensitivity of permeability is much significant than the stress sensitivity of porosity. Therefore, most studies in the literature only focus on the stress sensitivity of permeability (Gao et al., 2005; Yu et al., 2007).

The research on the stress sensitivity of permeability for tight oil reservoir has attracted attentions in laboratory studies (Guo et al., 2007; He et al., 2012; Jones, 1975; Li, 2006; Li and Li, 2013; Worthington, 2008; Zhu et al., 2012; Zhu et al., 2011). It is found, however, that most measurements on rock stress sensitivity are based on an individual method, i.e. variable confining pressure (VCP) or variable pore pressure (VPP). Meanwhile, the studies in the literature are limited to conventional reservoirs (Guo et al., 2008; Jiao et al., 2011; Kilmer et al., 1987; Li et al., 2006; Liu et al., 2008; Ren et al., 2012; Wang et al., 2014; Xiao et al., 2010; Zhou and Bai, 2012), while there are only a few studies investigating the stress sensitivity of unconventional reservoirs (Aybar et al., 2015; Kang et al., 2006; Song and Zheng, 2006; Yang et al., 2017, 2013). To shed more light on the stress sensitivity of unconventional oil reservoirs and fill the gaps in the literature, a systematic study on the stress sensitivity of permeability was carried out in this study using both tight sandstone and limestone rock samples. In particular, both VCP and VPP methods were used to determine the stress sensitivity of permeability in tight sandstone and limestone reservoirs at reservoir conditions. In addition, the pore structure of tight sandstone and limestone was analyzed using casting thin section imaging and scanning electron microscopy (SEM), respectively, to reveal the influential factors of stress sensitivity of permeability. To the end, the performance of oil production for stress-sensitive tight reservoirs was analyzed to elucidate the production characteristics of tight reservoirs, and meanwhile, several suggestions on the development strategy of tight reservoirs were also provided to improve the oil production of tight reservoirs.

Experimental methods and procedures

The experiment method used in this study is in reference to SY/T 5358-2010 “Formation damage evaluation by flow test”. A Quizix Q5000 pump (piston pump, which can operate at high precision and ultra-low speed) and a pressure sensor (TRAFAG 8251) were used in the experiments (Figure 1). The key parameters in the experiments are listed as follows: the maximum pressure is 10,000 psi, the maximum flow rate is 15 ml/min and the experimental temperature is 60°0 which is the average temperature of the tight reservoirs. The effective stress is 2–35 MPa in these experiments, which covers the range of the effective stress changes in the reservoirs.

Figure 1.

Main experimental devices. (a) Confining pressure variation equipment. (b) Pore pressure variation equipment. (c) Quizix Q5000 pump. (d) Core holder.

Preparation of core samples

In this study, nine tight sandstone cores and nine tight limestone cores in Sichuan Basin were used in the stress sensitivity tests of permeability (Figure 2). Prior to the tests, the experimental core samples were prepared according to the following procedures: first, several piston-like core samples, with a diameter of 2.5 cm, were extracted from the original large core samples; second, these core samples were then cleaned by solvents (e.g. alcohol and benzene); third, the core samples were dried at 65°C in a vacuum oven to a constant weight, and finally the length and the diameter of the dry samples were measured. The basic parameters of the core samples are shown in Table 1.

Figure 2.

Pictures of core samples. (a) Tight sandstone. (b) Tight limestone.

Table 1.

Basic parameters of the core samples.

Lithology	Experimental method	Core sample number	Experimental number	Well name	Strata	Depth(m)	Porosity(%)	Initial permeability (mD)
Tight sandstone	Variable confining pressure	10-SD-12	1	G-46	Shadi	2197.40	6.46	0.066
		38-L2-10	2	HC-X1	Liang_2	1471.80	2.95	0.007
		41-L-4	3	J-95	Liangshang	2493.90	2.35	0.055
	Variable pore pressure	3-S1-22	4	G-104	Sha_1	2559.00	2.41	0.059
		38-L1-8	5	HC-X2	Liang_1	1409.80	2.48	0.131
		38-L2-2	6	HC-X3	Liang_2	1460.80	1.54	0.200
		27-L12-1	7	X-56	Liang_1_2	1706.00	1.60	0.011
		23-L1-9	8	X-20	Liang_1	1682.90	1.74	0.009
		37-L12-2	9	X-9	Liang_1_2	1846.50	1.73	0.031
Tight limestone	Variable confining pressure	40-D1-2	10	L-X2	Da_1	1714.34	1.15	0.208
		9-D3-1	11	G-4	Da_3	2439.42	0.33	0.006
		34-D1-8	12	G-6	Da_1	2062.00	0.012	0.012
	Variable pore pressure	9-D3-4	13	G-5	Da_3	2439.88	0.65	0.231
		29-D3-4	14	J-8	Da_3	2778.20	0.91	0.63
		30-D13-3	15	J-53	Da_1_3	2847.15	1.13	0.024
		34-D1-7	16	W-6	Da_1	2060.80	1.27	0.014
		42-D2-7	17	C-2	Da_2	1914.40	1.56	0.010
		23-D1-11	18	X-30	Da_1	1847.80	1.13	0.007

Experiment procedures

Prior to the stress sensitive experiments, the gas permeabilities of tight sandstone and limestone samples were first measured. In fact, the permeability of rock measured with a flow media of gas (not liquid) is usually termed to as the Klinkenberg permeability in petroleum industry. More specifically, the gas permeability for each core sample was measured with five different pressures and flow rates using the nitrogen gas. The Klinkenberg permeability was obtained by a linear regression method, namely, fitting the five experimental points (the permeabilities and the pressure derivatives) with a straight line, and the intersection of the line and its ordinate is the Klinkenberg (1941) permeability. Second, the porosities of the core samples were measured by: vacuuming the core samples for more than 24 h, saturating the core samples with synthetic formation water under 10 MPa and then weighing these wet core samples to calculate the porosity. Finally, the stress sensitivity tests were carried out with VCP and VPP methods, separately. In the VCP method, the outlet of the core sample was connected to the atmosphere. The inlet pressure of the core was kept constant during the experiment, while the effective stress of the core was varied by changing the confining pressure (CP). In the VPP method, a variable back pressure was exerted to the outlet of the core sample; however, the original back pressure remained to be the same as the original reservoir pressure. Meanwhile, the CP was kept constant to simulate a constant overburden pressure (Gong and Xie, 1989; Wu et al., 1999). The effective stress of the core was varied by changing the back pressure. The stress sensitivity of permeability was tested by the following procedures: (a) the initial effective stress was used as the starting point, then the effective stress was increased slowly, with an interval of 4 MPa, until a maximum value was reached. (b) At each pre-set effective stress point, the permeability was measured when the gas flow stabilized. (c) The effective stress was gradually reduced to the initial effective stress, with an interval of 4 MPa, after reaching the maximum value. At each pre-set effective stress point, the permeability was measured when the gas flow stabilized. A schematic diagram of the experimental setup is shown in Figure 3.

Figure 3.

Flow chart of the experiment.

Analysis of results

In this paper, the stress sensitivity of the permeability for tight sandstone and limestone samples was tested by two methods VCP and VPP. In the VCP method, the CP increases first followed by a decrease, by which the effective stress increases first and then it decreases. In the VPP method, the pore pressure decreases first followed by an increase; therefore, the effective stress changes in the same way as the former method. The stress sensitivity of permeability can be estimated by three formulas (SY/T 5358-2010) $K_{PLP} = \frac{K_{I} - K_{PMA}}{K_{I}}$ (1) $K_{PLD} = \frac{K_{I} - K_{PMI}}{K_{I}}$ (2) $K_{R} = \frac{K_{PLP} - K_{PLD}}{K_{PLP}}$ (3)where K_PLP is the permeability loss rate in pressurizing (%); K_I is the permeability under initial effective stress (mD); K_PMA is the permeability under maximum effective stress (mD); K_PLD is the permeability loss rate in depressurizing (%); K_PMI is the permeability under minimum effective stress (mD); K_R is the permeability recovery rate (%).

Stress sensitivity experiments of the tight sandstone

Figures 4(a) and 5(a) show the experimental results of permeability for the tight sandstone measured by the VCP method. It can be seen that the permeability of the core sample decreases with an increase in the effective stress, showing a significant stress sensitivity in the permeability of tight sandstones. In addition, the decrease in permeability is found to be very quick with an effective stress of 10–20 MPa, while the decrease in permeability slows down when the effective stress increases from 20 MPa to 33.3 MPa (Yang et al., 2017). To the end, the K_PLP value is larger than 70% when increasing the effective stress from 9.3 MPa to 33.3 MPa. On the other hand, a pressure drawn-down test was carried out when the effective stress rises to 33.3 MPa. It is found that the permeability increases gradually with a decrease in the effective stress, indicating a slow recovery of the permeability. However, when the effective stress decreases to the initial stress (i.e. 9.3 MPa), the K_PLD value (irreversible loss) is larger than 40%, and the recovery in permeability (or K_PR) for the tight sandstone is 26.9%–42.87%.

Figure 4.

Stress sensitivity curve of the tight sandstone and limestone. (a) VCP (sandstone). (b) VPP (sandstone). (c) VCP (limestone). (d) VPP (limestone).

Figure 5.

The stress sensitivity of permeability for the (a) tight sandstone and (b) tight limestone.

Figures 4(b) and 5(a) show the experimental results of permeability for the tight sandstone measured by the VPP method. The permeability of the core sample also decreases with the increase in the effective stress, and the K_PLP value is larger than 64%. Similar to the VCP method, the pressure drawn-down test was carried out when the effective stress increases to 24 MPa. The permeability increases with the decrease in the effective stress. When the effective stress decreases to the initial stress, the K _PLD value is larger than 33%; therefore, the value of K_PR ranges from 26.73% to 48.36%.

Stress sensitivity experiments of the tight limestone

Figures 4(c) and 5(b) show the experimental results of permeability for the tight limestone measured by the VCP method. The permeability of the core sample is found to drop rapidly with the increase of the effective stress from 10 MPa to 20 MPa, and then it decreases slowly with a further increase in the effective stress from 20 MPa to 35 MPa. In consequence, the K_PLP value is larger than 72%. When the effective stress rises to 35MPa, a pressure drawn-down test is carried out as well. It is observed that the permeability increases gradually with the decrease in the effective stress. When the effective stress decreases to the initial stress (i.e. 10 MPa), the K_PLD value is larger than 52%, and hence the K_PR value is 15–32%.

Figures 4(d) and 5(b) show the experimental results of permeability for the tight limestone measured by the VPP method. The permeability of the core sample decreases with an increase in the effective stress, and the K_PLP value is found to be larger than 56%. When the effective stress increases to 24 MPa, a pressure drawn-down test is carried out. The permeability gradually increases with the decrease in the effective stress. When the effective stress decreases to the initial stress, the K_PLD value is larger than 46%, and the K_PR ranges from 15% to 22%.

From the above experiment results, it can be concluded that the loss in permeability by increasing effective stress is very high (e.g. K_PLP>56.67%), while the recovery of permeability by decreasing the effective stress is low (e.g. K_PR<48.36%), for both tight sandstone and limestone rocks. It thus indicates that an elastic–plastic deformation of the pore structure, rather than a net elastic deformation, occurs with the change of effective stress for the tight sandstone and limestone rocks. Moreover, the irreversible plastic deformation dominates over the elastic part of the deformation.

Comparison on the stress sensitivity between different core samples

The relationship between K_PLP and the permeability (K) of the tight sandstone and limestone measured by the VPP method is shown in Figure 6. It can be seen that the stress sensitivity of the sandstone is greater than that of the limestone. In addition, the K_PLP of the sandstone and limestone goes up slowly with the decline of initial permeability of the core. That is, the stress sensitivity increases gradually with the decline of initial permeability of the core.

Figure 6.

The relationship between K_PLP and K for the tight sandstone and limestone.

The difference in the stress sensitivity of permeability between the tight sandstone and the tight limestone can be attributed to the differences in their mineral compositions and types of pore structure. The Jurassic tight sandstone in the Sichuan tight oil reservoir is primarily comprised of sand grains cemented by mud. The pores are mainly composed of isolated intergranular pores and intergranular dissolved pores. Figure 7(a) shows a casting thin section of the tight sandstone, which suggests that the pores are connected by narrow throats. In direct contrast, the Jurassic tight limestone in the Sichuan tight oil reservoir is composed by bivalve bioclastic particles with calcite crystals distributed between these particles. Figure 7(b) shows an SEM image of the tight limestone, which suggests that the bivalve particles present in the form of strips, and meanwhile, both micro- and nanoscale fractures are found to develop on these interstitial materials.

Figure 7.

(a) Casting thin section of the tight sandstone and (b) SEM image of the tight limestone.

It has been reported that when the pressure of the tight reservoir decreases, the throats are first compressed, instead of the pores, to primarily control the permeability of the tight sandstone (Ruan and Wang, 2002; Xiang et al., 2002). Hence, the size and the shape of the throats are the main factors contributing to the stress sensitivity of the rock permeability (Buchsteiner et al., 1993; Fatt and Davis, 1952). In this study, the connectivity of the tight sandstone is poor because it is mainly determined by narrow throats, as observed from the image of casting thin section. Therefore, the stress sensitivity in the permeability of the tight sandstone is strong. In tight limestone, despite the pore–throat structure, a lot of micro–nano fractures can be observed from the SEM image. These tiny fractures serve as both reservoir space and flow channel. Thus, the connectivity of the tight limestone is better than that of the tight sandstone. As a consequence, the stress sensitivity of the tight limestone is lower than that of the tight sandstone.

Comparison on the stress sensitivity between VPP and VCP methods

In this study, both VPP and VCP methods are used to analyze the stress sensitivity of the permeability. To compare these two methods, the experimental permeability from stress sensitivity tests for limestone is used as an example, and the results are shown in Figure 8. It is observed that the stress sensitivity of permeability measured by the VCP method is greater than that measured by the VPP method. In fact, the overburden pressure (i.e. CP) of the reservoir remains constant with the recovery of oil and gas, while the pore fluid pressure in the reservoir changes dynamically. Hence, the experimental results measured by VPP method can reflect the actual development of the tight reservoir (Tian et al., 2015). On the contrary, the experimental results by the VCP method can overestimate the stress sensitivity of the reservoir due to the variations in the CP. It also can be concluded that the K_PLD value of the tight limestone measured by VCP and VPP methods increases gradually with the decrease in the initial permeability of the core sample, the stress sensitivity of the permeability increases step by step with the decrease in the initial permeability in Figure 8. In other words, a tighter limestone reservoir in general possesses much greater stress sensitivity than a conventional limestone reservoir.

Figure 8.

The relationship between K_PLD and K of limestone.

Development characteristics of the stress-sensitive tight reservoir

The oil production data of two volume fracturing horizontal well A and well B in the tight sandstone reservoir M, and two volume fracturing horizontal well C and well D in the tight limestone reservoir N were analyzed to evaluate the development characteristics of the stress-sensitive tight reservoirs. From the stress sensitivity experiments, we have known that the stress sensitivity of permeability for M (sandstone) and N (limestone) reservoirs are very strong. However, the stress sensitivities of permeability for wells A and B are similar, and those of wells C and D are similar as well. In addition, wells A and C produce by means of amplifying the producing pressure drop, while wells B and D produce by controlling the producing pressure drop.

In Figure 9, it is shown that the oil productions of wells A and C are high at initial stage but the productions decrease rapidly afterwards, and the cumulative productions of well A or C are low. In contrast, the initial oil productions of wells B and D are relatively low, and meanwhile, the productions decrease slowly, and the cumulative productions are relatively high. Therefore, for tight reservoirs with high stress sensitivity, the producing pressure drop can be controlled by selecting a reasonable producing pressure drop to reduce the damage in permeability caused by the stress sensitivity, and thus decreases the decline rate of oil production. To this end, a higher cumulative production from a single well can be achieved due to the maintenance of a much longer stable production period for the single well.

Figure 9.

Dynamic production curve of spatial fracturing horizontal wells. (a) Well A and Well B. (b) Well C and Well D.

Conclusions

This paper presents an experimental study of the stress sensitivity of tight sandstone and limestone reservoirs. The main conclusions of this study can be summarized as follows:

In the stress sensitivity experiments by VCP and VPP methods, it is found that both tight sandstone and limestone reservoirs have strong stress sensitivity of permeability, showing that the tight reservoir with a smaller initial permeability has a higher K_PLP value and a smaller recovery rate. It thus indicates that a tighter reservoir in general possesses a much greater stress sensitivity than a conventional reservoir.

From the above experiment results, it can be concluded that the loss in permeability by increasing effective stress is very high (e.g. K_PLP>56.67%), while the recovery of permeability by decreasing the effective stress is low (e.g. K_PR<48.36%), for both tight sandstone and limestone rocks. It thus indicates that an elastic–plastic deformation of the pore structure occurs with the change of effective stress for the tight sandstone and limestone rocks.

From the observation of the casting thin section, it is found that the connectivity in sandstone rocks is primarily determined by narrow throats, introducing strong stress sensitivity of permeability for tight sandstone reservoirs, while plenty of micro–nano fractures can be observed from the SEM image of tight limestone, introducing relatively weak stress sensitivity of permeability for tight limestone reservoirs.

VCP method overestimates the stress sensitivity of the reservoir, whereas the VPP method can better reflect the stress sensitivity during the development of the reservoir. However, the results of both methods suggest that the recovery of the permeability for tight sandstone and limestone reservoirs is very low with the backup of pressure, indicating an irreversible effect of stress sensitivity for tight reservoirs.

By analyzing the oil productions from several wells in tight reservoirs, it is found that for tight reservoirs with high stress sensitivity, the initial oil production drops quickly, while for tight reservoirs with low stress sensitivity, the oil production can maintain high and stable for a long period of time. Therefore, the oil production of tight reservoirs can be controlled by lowering the pressure drop in order to reduce the damage in permeability caused by the stress sensitivity.

Footnotes

Acknowledgements

The authors wish to thank Dr Hongna Ding,Dr Rui Wang,Dr Zepu Tian and Xianing Li who contributed to this research.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research,authorship,and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research,authorship,and/or publication of this article: This research was supported by the National Key Technology Research and Development Program of China during the 13th Five-Year Plan “Gas Injection Technology on Tight and Low Permeability Reservoirs for Ordos Basin (2016ZX05048003)”.

References

Aybar

Eshkalak

et al . (2015) Evaluation of production losses from unconventional shale reservoirs. Journal of Natural Gas Science and Engineering 23: 509–516.

Buchsteiner

Warpinski

Economides

(1993) Stress-induced permeability reduction in fissured reservoirs. In: The SPE annual technical conference and exhibition, Houston, USA, 3–6 October 1993.

Fatt

Davis

(1952) Reduction in permeability with overburden pressure. Journal of Petroleum Technology 4(12): 16–16.

Gao

Zhou

Peng

(2005) Study on the stress sensitivity of reservoir porosity. Petroleum Geology & Experiment 27(2): 197–202.

Gong

Xie

(1989) A review of laboratory investigation of rock permeability. Chinese Journal Rock Mechanics and Engineering 8(3): 219–227.

Guo

Deng

Liu

et al . (2008) Test and application of multiple stress sensitivity of low permeability gas reservoir. Journal of Southwest Petroleum University 30(2): 78–82.

Guo

Zhang

et al . (2007) Study on core stress sensitivity for gas reservoir with two experiment method. Journal of Southwest Petroleum University 29(2): 7–9.

Kang

You

et al . (2012) Effects of mineral composition and microstructure on stress sensitivity of mudrocks. Natural Gas Geoscience 23(1): 129–134.

Jiao

Xie

et al . (2011) An experimental study on stress dependent sensitivity of ultra-low permeability sandstone reservoirs. Acta Petrolei Sinica 32(3): 489–494.

10.

Jones

(1975) A laboratory study of the effects of confining pressure on fracture flow and storage capacity in carbonate rock. Journal of Petroleum Technology 27: 21–27.

11.

Kang

Zhang

Chen

et al . (2006) Comprehensive research of tight sandstones gas reservoirs stress sensitivity in Daniudi Gasfield. Natural Gas Geoscience 17(3): 335–338.

12.

Kilmer

Morrow

Pitman

(1987) Pressure sensitivity of low permeability sandstones. Journal of Petroleum Science & Engineering 1(1): 65–81.

13.

Klinkenberg

(1941) The permeability of porous media to liquids and gases. In: Drilling and production practice, API, pp.200–213.

14.

(2006) Evaluation method for stress sensitivity of reservoir rock. Petroleum Geology & Oil Field Development in Daqing 25(1): 40–42.

15.

(2013) Error analysis of experimental evaluation methods for stress sensitivity of reservoir. Natural Gas Industry 33(2): 48–51.

16.

Qiao

Chen

(2006) Experimental and theoretical study on rock stress sensitivity in low permeability sandstone. Drilling & Production Technology 29(4): 91–93.

17.

Liu

Wang

et al . (2008) Laboratory study on the stress sensitivity in EB tight rock. Drilling & Production Technology 31(5): 86–89.

18.

Liu

Yang

Yao

et al . (2017) Pore-scale remaining oil distribution under different pore volume water injection based on CT technology. Advances in Geo-Energy Research 1(3): 171–181.

19.

Rashid

Glover

PWJ

Lorinczi

et al . (2017) Microstructural controls on reservoir quality in tight oil carbonate reservoir rocks. Journal of Petroleum Science & Engineering 156: 814–826.

20.

Ren

Zhao

et al . (2012) Experiment evaluation of stress sensitivity of low-permeability sandstone to confining pressure. Marine Geology Frontier 28(6): 60–64.

21.

Ruan

Wang

(2002) Low-permeability oilfield development and pressure-sensitive effect. Acta Petrolei Sinica 22(2): 73–76.

22.

Song

Zheng

(2006) S tress sensitivity of low permeability tight gas reservoir and its effect on single well productivity. Petroleum Geology & Oil Field Development in Daqing 25(6): 47–49.

23.

National Energy Administration (2010) Formation damage evaluation by flow test: SY/T 5358 –2010. Beijing: Petroleum Industry Press.

24.

Tian

Zhu

et al . (2015) Study on testing method of back-pressure stress sensitivity evaluation. Natural Gas Geoscience 26(2): 377–383.

25.

Wang

Liao

et al . (2014a) A study on development effect of horizontal well with SRV in unconventional tight oil reservoir. Journal of the Energy Institute 87(2): 114–120.

26.

Wang

Liao

Zhao

(2015) Study of tight oil reservoir flow regimes in different treated horizontal well. Journal of the Energy Institute 88(2): 198–204.

27.

Wang

Ran

Liao

(2017) Pressure transient responses study on the hydraulic volume fracturing vertical well in stress-sensitive tight hydrocarbon reservoirs. International Journal of Hydrogen Energy 42(29): 18343–18349.

28.

Wang

Duan

et al . (2014b) Stress sensitivity experiment of sandstone reservoirs in deep section with high pressure and low-permeability. Geological Science and Technology Information 33(1): 90–94.

29.

Sun

(1999) The research and application of permeability, porosity and net overburden pressure laws. Journal of Southwest Petroleum Institute 21(4): 23–25.

30.

Worthington

(2008) A diagnostic approach to quantifying the stress sensitivity of permeability. Journal of Petroleum Science and Engineering 61(2–4): 49–57.

31.

Xiang

(2002) An experimental study of simulating high-speed production in tight sandstone gas reservoir. Journal of Chengdu University of Technology 29(6): 617–619.

32.

Xiao

Zhao

et al . (2010) Laboratory study of stress sensitivity to permeability in tight sandstone. Rock and Soil Mechanics 31(3): 775–779.

33.

Yang

Liu

Sun

et al . (2017) Research on stress sensitivity of fractured carbonate reservoirs based on CT technology. Energies 10(11): 1833.

34.

Yang

Gao

Guo

et al . (2013) Effect of stress sensitivity on well productivity in tight gas reservoir. Drilling & Production Technology 36(2): 58–61.

35.

Xiong

Gao

et al . (2007) Stress sensitivity of tight reservoir and its influence on oilfield development. Acta Petrolei Sinica 28(4): 95–98.

36.

Zhu

Jiang

et al . (2012) An experimental analysis of sensitivity of the Jiulongshan conglomerate reservoirs in west Sichuan Basin. Natural Gas Industry 32(9): 40–43.

37.

Zhu

Wang

Shi

et al . (2011) Experimental study on pressure-sensibility of fractured shale reservoir. Science Technology and Engineering 11 (35): 8862–8864.

38.

Zhou S a nd Bai

, (2012) Chang 8 ultra low permeability reservoir stress sensitivity lab experiment in Zhenjiang Oilfield. Petroleum Geology and Engineering 2(4): 110–112.

The stress sensitivity of permeability in tight oil reservoirs

Abstract

Keywords

Introduction

Experimental methods and procedures

Preparation of core samples

Experiment procedures

Analysis of results

Stress sensitivity experiments of the tight sandstone

Stress sensitivity experiments of the tight limestone

Comparison on the stress sensitivity between different core samples

Comparison on the stress sensitivity between VPP and VCP methods

Development characteristics of the stress-sensitive tight reservoir

Conclusions

Footnotes

Acknowledgements

Declaration of conflicting interests

Funding

References