Characteristics of Pore-Throat in Tight Sandstones of the Jurassic Ahe Formation in the Northern Tarim Basin

Tong Lin,Cong Tan,Hongxing Wei,Xu Zeng,Lei Zhao,Xing Zhang,Xin Nie,Lan Wang,Chenhao Sun

doi:10.1155/2022/1139232

Abstract

In order to clarify the characteristics of pore-throat in tight sandstone reservoirs in the Dibei area of the Kuqa Depression in the Tarim Basin (Northwest China) and to make clear its impact on reservoir quality and productivity, microscopic observation and quantitative analysis of 310 tight sandstones in the Kuqa Depression are carried out by using various methods. Microscopic observation shows that the shapes of the pores are flat, oval, and long-narrow. A great number of throats connect the nanoscale pores in the form of a network. Quantitative analyses including RCMP (rate-controlled mercury penetration), HPMI (high-pressure mercury injection), NA (nitrogen adsorption), and routine and stress-dependent core analysis show that the peak of pores radius ranges from 125 μm to 150 μm, and the throat radius is in the range of 1 μm-4 μm. The throat space accounts for about 2/3 of the total space of the tight sandstones, which is the major storage space for natural gas. The space shape has a great influence on the reservoir seepage capacity, particularly under the condition of overburden pressure. The pores with throat radius greater than 300 nm have free fluid, and they contribute more than 98% of the reservoir permeability. The pore spaces with throat radius among 300 nm-52 nm can release fluids by reservoir stimulation. The pore-throats with radius < 52 nm cannot release the irreducible hydrocarbon fluids. In addition, formation pressure is easy to destroy tight sandstone reservoir. The research results will provide insights into the efficient recovery of natural gas in tight sandstones.

Highlights

Porosity and permeability are two major parameters for evaluating reservoir quality, and there is usually a good linear correlation between them [1,2,3,4]
The main purpose of this study is to characterize the pore-throat of the tight sandstone reservoirs in the Dibei area of the Kuqa Depression in the Tarim Basin (Northwest China) and decipher the relationship between reserves and productivity with throat based on multiproxy of quantitative measurement
The main conclusions drawn from this thesis are as follows: (1) The sandstone gas reservoirs in the Dibei area are tight, with high matrix content and abundant clay minerals

Summary

Introduction

Porosity and permeability are two major parameters for evaluating reservoir quality, and there is usually a good linear correlation between them [1,2,3,4]. Nelson [13] has introduced the distribution of throat sizes in different types of rocks. Based on his measured data, it is believed that changes in throat size have the most significant impact on reservoir permeability. If the throat size changes by one order of magnitude, the permeability value will change by more than two orders of magnitude, so that throat is a critical parameter to evaluate reservoir quality. Pittman established a method to evaluate the quality of low-permeability reservoir by throat size as early as 1989 and achieved good results [14]. Reservoir quality evaluation with throat as a parameter, especially the evaluation of tight sandstone reservoirs, is relatively scientific and effective, and a lot of achievements have been made in related research ([14]; Lu et al, 1997; [15]; Wen et al, 2005; [16]; Li et al, 2007; [17, 18]; Li et al, 2012; [19])

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