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Rongze Y.,Petrochina | Rongze Y.,National Energy Shale Gas Research and Development Experimental Center | Xiaowei Z.,Petrochina | Xiaowei Z.,National Energy Shale Gas Research and Development Experimental Center | And 3 more authors.
Natural Gas Industry | Year: 2012

In order to understand the flow mechanism of shale reservoirs and analyze the controlling factors of their productivity, we performed extensive literature review, summarized the three stages of gas flow in the shale formations, namely desorption, diffusion and seepage flow, and analyzed their influential factors and application conditions. Numerical simulation methods were applied to study the influential factors of productivity of horizontal shale gas wells, such as adsorbed gas content, Langmuir volume, Langmuir pressure, diffusion coefficient, matrix permeability, micro-fracture permeability, hydraulic fracture conductivity, etc. The findings are as follows: (1) Assume that gas-in-place is constant, the higher the adsorbed gas content is, the lower the daily output and accumulative shale gas production at the same development stage are and the more rapidly the average reservoir pressure drops. (2) Assume that adsorbed gas contents are the same, the daily output and accumulative shale gas production at the same development stage are getting lower and the initial flow rate decline speeds up along with the increasing of Langmuir volume and Langmuir pressure. (3) The gas diffusion coefficient has a minor influence on productivity. (4) When being between 1. OX 10 -9 and 1. OX 10 -6 mD, matrix permeability will become the major factor controlling the productivity of horizontal shale gas wells. Daily output and accumulative production will increase rapidly along with the increasing matrix permeability. (5) When matrix permeability is larger than 1. OX 10 -6 mD, both matrix permeability and microfracture permeability are the major factors controlling the productivity of horizontal shale gas wells. Daily output and accumulative production will increase along with the increasing of matrix permeability and microfracture permeability. (6) The accumulative gas production of horizontal wells increases progressively but the amplitude of production growth decreases along with the increasing of conductivity of hydraulic fractures with optimum conductivity. Source


Xue H.,Tsinghua University | Xue H.,Petrochina | Xue H.,China National Petroleum Corporation | Xue H.,National Energy Shale Gas Research and Development Experimental Center | And 15 more authors.
Shiyou Xuebao/Acta Petrolei Sinica | Year: 2013

TOCs of Longmaxi Formation source rocks and gas-content measurements of shale gas wells in the Zhaotong block, Sichuan Basin showed that the gas content of lower-interval shales is better and the brittleness index of lower-interval reservoirs also indicated adjacent shale formations suitable for stimulation. Based on bulk rock and clay mineral analyses as well as experiments of isothermal adsorption, specific surface areas and aperture distributions, the organic matter (kerogen) in shales was found abundant in well-developed nano-pores with an aperture of 2-60 nm, which are major contributors to the specific surface area of shales. This can be also implied by the adsorption and desorption curves of kerogens to and from shales because the shape of the curves is generally alike, having a hysteresis loop. However, the clay in shales shows a certain specific surface area whose content has no relationship with the specific surface area of shales. Therefore, with the increase of TOC, the specific surface area of shales increases and their adsorption capacity strengthens as well, resulting in an increase in the saturated adsorption capability and gas content. Source

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