An experimental study on stress sensitivity of tight sandstone gas reservoirs during nitrogen drilling
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ORIGINAL PAPER
An experimental study on stress sensitivity of tight sandstone gas reservoirs during nitrogen drilling Meng Yingfeng 1 & Luo Chengbo 1 & Li Gao 1 & Liu Houbin 1 Received: 6 January 2017 / Accepted: 4 September 2019 # Saudi Society for Geosciences 2019
Abstract The “Fizz Phenomenon,” observed by real-time monitoring and reservoir evaluation technology while nitrogen drilling, is ubiquitous in tight sandstone gas reservoirs. Experiments are used to simulate stress sensitivity when encountering tight gas reservoirs in the Xujiahe formation of the central and western Sichuan Basin. The original reservoir effective stress is assumed to be the effective confining pressure reflecting the real severity of damage to the formation permeability. Results show that 1) the permeability of samples reduces with confining pressure increasing and pore pressure reducing. 2) The denser the rock, the stronger stress sensitivity is, which can explain the mechanism of low permeability reservoir sensitivity differences by using Xray diffraction (XRD), scanning electron microscopy (SEM), casting thin sections, and constant-speed mercury injection experiment. What’s more, throat size and shape and plastic mineral content and type contribute to the differences of permeability sensitivity. 3) Mineral content and type of plastic are the major factors affecting the sensitivity of permeability differences. The stress sensitivity of tight reservoir permeability rock becomes strong with the increase of plastic mineral content. Keywords Tight sandstone . Pore and throat structure . Plastic mineral . Stress sensitivity
Introduction Stress sensitivity means the influence of pressure difference produced by joint working of the matrix stress and the porous fluid pressure on the porous microstructure. There exists distinct fluid-solid coupling effect during seepage in low permeability rock. Because of the disordered and complicated structure of porous media, reports using analytical methods and numerical methods to study stress-dependent permeability are scarce. The relevant correlations are summarized in Table 1. Stress sensitivity of reservoir permeability was proposed by (Fatt and Davis 1952). Since then, many researchers have focused on this problem. Ostensen (1986) adopted a modified pseudo-pressure considering stress dependence and studied the effect of stress-dependent permeability on gas production Responsible Editor: Abdullah M. Al-Amri * Luo Chengbo [email protected] 1
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Cheng du, Si chuan, China
and well testing in tight gas sands. Zarool et al. (1995) presented a study that verified stress sensitivity in the Dulang field and how it is related to productivity. Chin et al. (1998) proposed a fully coupled geomechanics and single-phase fluid flow model to evaluate the combined effects of stress, fluid flow, and reservoir property changes on well response in stress-sensitive reservoirs. Jin et al. (2000) presented the results o
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