A new dynamic capillary-number-recovery evaluation method for tight gas reservoirs

Zhao, Fulei; Liu, Pengcheng; Hao, Shengye; Qiu, Xinyu; Shan, Ce; Zhou, Yanglei

doi:10.1016/j.petrol.2021.108730

Cited by 7 publications

(3 citation statements)

References 42 publications

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“…In tight gas reservoirs, the radius of the fluid flow channel is small, and the water films at narrow pore throats generate a large flow resistance, even potentially forming a water blockage in the gas–water flow channel. − The gas needs to overcome the capillary resistance to break through the water blockage, and then the gas can start to flow through the pore throat during CO 2 injection. , The threshold pressure effect appears during the gas–water transport in tight rock. , The smaller pore-throat size leads to a larger capillary resistance. The water distribution in the rock is mainly controlled by the pore-throat microstructure; consequently, the rock pore-throat microstructure has a significant impact on the threshold pressure. , …”

Section: Introductionmentioning

confidence: 99%

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

et al. 2022

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The simultaneous flow of gas and water is controlled by a threshold pressure gradient (TPG) effect during CO 2 injection of tight gas reservoirs. The TPG effect is dynamic because it varies with both the effective stress and the water saturation. The sensitivity of TPG to effective stress and mobile water is affected by the porethroat microstructure. In this paper, we report the results of dynamic TPG tests on six cores with similar permeability. The influence of the pore-throat microstructure on the sensitivity of the TPG to stress and to mobile water was also quantitatively studied using a fractal method, and the distribution of the threshold pressure and corresponding gas production loss were calculated during CO 2 injection in tight gas reservoirs. The test results show that TPG decreases logarithmically with the increase of the pore fluid pressure during CO 2 injection, a change of 0.1−50 MPa in the pore fluid pressure corresponding to a 1.8−3.5 times increase of the TPG variation. The TPG increases exponentially by 3.5−6.7 times from irreducible water saturation to a mobile water saturation of 30%. The fractal dimension (D) of the heterogeneity of the rock pore-throat microstructure has a linear relationship with both the stress sensitivity coefficient (λ) and mobile water sensitivity coefficient (η), with the larger values of λ and η being associated with more heterogeneous pore-throat microstructures. The reservoir threshold pressure showed a significant nonlinear distribution in near-well reservoirs at low bottom-hole flow pressures of the production well during CO 2 injection. The calculated gas well production loss as a result of a dynamic threshold pressure is 7−16% higher than that of the fixed threshold pressure, and the difference is larger at low pressures.

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Section: Introductionmentioning

confidence: 99%

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

et al. 2022

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“…The main reason for this is that oil is replaced by imbibition [25]. Owing to the pore-scale effect, the production of tight reservoirs is a complex crossscale process: from the unreformed area to the area affected by the hydraulic fractures to the hydraulic cracks and finally to the wellbore [26][27][28][29]. The main research object of this study was an unreformed tight oil reservoir (Figure 10).…”

Section: Conceptual Modelmentioning

confidence: 99%

Division Method and Seepage Law of Seepage Channels in a Tight Reservoir

Fang

et al. 2021

Geofluids

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Tight oil reservoirs are characterized by a low porosity, low permeability, and strong heterogeneity. The macropores, throats, and microcracks in reservoirs are the main seepage channels, which affect the seepage law in the reservoirs. In particular, oil-water two-phase flow in different types of pores requires further study. In this study, two groups of online NMR displacement experiments were designed to study the seepage characteristics of tight oil reservoirs. It was found that the main seepage channels for oil-water two-phase flow are the microcracks, large pores, and throats in the reservoir. The large pores are mainly micron and submicron scale in size. The oil in the small pores is only transferred to the large pores through imbibition to participate in the flow, and there is no two-phase flow. Based on the influence of different pore structures on the seepage law of a tight reservoir, the pores were divided into seepage zones, and a multistage seepage model for tight reservoirs was established. Based on this model, the effects of the imbibition, stress sensitivity, threshold pressure gradient, and Jamin effect on model’s yield were studied. The results show that imbibition is no longer effective after a while. Owing to the stress sensitivity, the threshold pressure gradient, and the Jamin effect, oil production will be reduced. As the parameter value increases, the oil production decreases. The production decreases rapidly in the early stage of mining while decreases slowly in the later stage, exhibiting a trend of high yield in the early stage and stable yield in the later stage.

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“…Tight sandstone gas reservoirs have huge gas reserves and very significant potential for development. − However, these reservoirs have low or ultra-low porosity/permeability, high water saturation, strong heterogeneity, and complex gas–water seepage (flow of gas–water in rock pore throats). − The water film in the complex and fine pore throats of tight gas reservoir rocks produces greater resistance to seepage. − The gas in the pore throats needs to break through, overcoming the capillary resistance to flow from the static state . Consequently, a certain displacement differential pressure is required initially to counteract this resistance, to start and then to maintain the gas flow along the pore throat path.…”

Section: Introductionmentioning

confidence: 99%

Improving the Prediction of Production Loss in Heterogeneous Tight Gas Reservoirs Using Dynamic Threshold Pressure

et al. 2022

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Tight gas reservoirs commonly exhibit complex pore throat structures. Conventionally, a constant threshold pressure gradient (TPG) has been used to predict the production loss that arises from overcoming the rock's disinclination to flow water and gas through such complex pore throat structures. In this work, we find that the TPG is not constant during the production lifetime of a reservoir. The TPG varies significantly with both effective stress and water saturation, leading us to rename TPG as dynamic threshold pressure gradient (DTPG). In the first part of this paper, we examine the sensitivity of DTPG to stress and mobile water saturation for cores with different permeabilities, showing that DTPG increases logarithmically with effective stress from 0.17 to 0.5 MPa/m for a change in effective stress from 0.6 to 30.5 MPa. The DTPG also increases exponentially with mobile water saturation (S m ), which is 2.7−6.5 times higher at S m = 25% compared to the value at irreducible water saturation. The sensitivity of DTPG to both variables shows a decreasing power law trend with increasing rock permeability. These combined effects generally suggest that DTPG is larger than the conventional TPG. In the second part of this paper, we model the effects of using a variable DTPG in place of a constant TPG for the purpose of predicting the production loss associated with the latent pressure barrier in different heterogeneous reservoirs. When the interacting effects of effective stress, water saturation, and permeability are taken into account, we find that the threshold pressure is relatively small in heterogeneous reservoirs with a distribution of increasing permeability in the gas flow direction. The constant TPG approach underestimates the production loss by 34−45% with the greatest difference occurring at low gas pressures encountered at the production well, suggesting that gas production wells should be located in areas with high permeability.

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A new dynamic capillary-number-recovery evaluation method for tight gas reservoirs

Cited by 7 publications

References 42 publications

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

Division Method and Seepage Law of Seepage Channels in a Tight Reservoir

Improving the Prediction of Production Loss in Heterogeneous Tight Gas Reservoirs Using Dynamic Threshold Pressure

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A new dynamic capillary-number-recovery evaluation method for tight gas reservoirs

Cited by 7 publications

References 42 publications

Quantifying Controls on Threshold Pressure during CO2 Injection in Tight Gas Reservoir Rocks

Quantifying Controls on Threshold Pressure during CO2 Injection in Tight Gas Reservoir Rocks

Division Method and Seepage Law of Seepage Channels in a Tight Reservoir

Improving the Prediction of Production Loss in Heterogeneous Tight Gas Reservoirs Using Dynamic Threshold Pressure

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Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks