Study on Variation Laws of Fluid Threshold Pressure Gradient in Low Permeable Reservoir

Mingwei Zhao,Caili Dai,Mengjiao Cao,Haonan He

doi:10.3390/en13143704

Mingwei Zhao, Caili Dai + Show 2 more

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https://doi.org/10.3390/en13143704

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Journal: Energies	Publication Date: Jul 18, 2020
Citations: 5	License type: CC BY 4.0

Affiliation: China University of Petroleum, East China

Abstract

A study on the seepage characteristics and laws of nano-micron pore throat in a low permeable reservoir matrix is of great significance for promoting high efficacy of low permeable reservoirs. Threshold pressure gradient (TPG) is an essential factor to reflect the seepage law. Here, variation laws of TPG and its influencing factors of low reservoir fluid are analyzed systematically through physical simulation experiment. Throat diameter distribution of cores was measured by a mercury injection method, and it was found that with the decrease of pore throat median diameter, TPG increase appeared slowly first and fast afterwards. The patterns of the TPG with permeability in water and oil were compared. Results showed that the TPG versus permeability gave power functions in a form and the TPG in oil was more than two times larger than that of water. Besides, TPG in two-phase flow was investigated by the stabilization method. Tests revealed that the higher the oil saturation, the greater the TPG value, and the TPG in two-phase flow is always higher than that of single-phase flow under the same conditions, which function as the combined action of the capillary force. In addition, the effects of core length, fluid type, and core wettability on the TPG were studied systematically, which has guiding significance for the development of a low permeability reservoir.

Highlights

In recent years, studies on unconventional reservoirs such as low permeability and shale reservoirs have attracted extensive attention [1,2,3,4,5,6,7]
A low permeability reservoir has the characteristics of small pore throat, low permeability, prominent capillary phenomenon and complex structure, which leads to the great difference of its seepage mechanism and oil–water migration law from conventional reservoirs [6,7,8,9,10,11,12,13,14]
The results demonstrate that the filtration capacity of reservoir fluid can be characterized by permeability, and by pore throat median diameter

Summary

Introduction

Studies on unconventional reservoirs such as low permeability and shale reservoirs have attracted extensive attention [1,2,3,4,5,6,7]. Main research results indicate that fluid flow in low permeability reservoirs has obvious characteristics of non-Darcy flow and no longer conforms to Darcy’s law [15,16,17]. The characteristics of non-Darcy seepage flow are typically nonlinear, that is, the flow velocity is obviously lower than Darcy flow or the nonlinear section appears when the pressure gradient is small. When the pressure gradient is lower than TPG, the fluid cannot flow. At this point, the relationship between the pressure gradient and flow velocity is not a simple linear relationship, but a complicated nonlinear relationship [21,22,23]. When the pressure gradient increases to a certain value, the relationship between the pressure gradient and the flow rate is close to a linear relationship [23,24,25,26,27,28]

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