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Zhao Q.,China University of Geosciences | Zhao Q.,Petrochina | Zhao Q.,National Energy Shale Gas R and perimental Center | Wang H.,Petrochina | And 7 more authors.
Natural Gas Industry | Year: 2013

The shale gas volume lost during the shale core desorption test is calculated by the analytical method that is regularly used in the coal-bed methane desorption test at present. However, the analysis of the measured desorption test data of shale cores reveals that the time of shale coring is usually long and the heterogeneity of porosity and permeability is strong due to the existence of natural fractures in cores (multiple straight lines in the desorption curves).These characteristics make this analytical method unsuitable to calculate the lost shale gas volume. Therefore, as the shale core canister desorption test process is similar to some extent to gas well recovery process with constant pressure under closed outer boundary, the Arps decline method was then proposed to calculate the lost shale gas volume in the desorption test. Three Arps decline patterns were used to match shale core desorption curves and the exponential decline method was found to be the best in matching with the measured data in the whole test interval. As a result, 20%-40% of the lost shale gas volume, underestimated by the previous analytical method, was calculated by the Arps exponential decline method. In conclusion, this new method, with few parameters needed and restrict prerequisite unnecessary, can reflect the influences of various factors on the shale core desorption, and is more suitable for calculating the lost gas volume during the shale core desorption test.

Zhang Q.,Petrochina | Zhang Q.,National Energy Shale Gas R and perimental Center | Zhang Q.,China National Petroleum Corporation | Liu H.,Petrochina | And 8 more authors.
Natural Gas Industry | Year: 2013

The determination of shale gas content is of great significance to the assessment of shale gas reserves and the identification of play fairway. Under the guidance of geologic theory, we performed a correlative analysis of factors that may influence shale gas content. In the Lower Silurian Longmaxi Fm shales in southeastern Chongqing, shale gas content may be influenced by various factors such as porosity, permeability, water saturation, TOC, Ro, clay content, quartz content, carbonate content and pyrite content. The effects of these potential factors are evaluated through normalized factors analysis, providing the criteria for eliminating the factors with minor effects on gas content from the initial set. Fast iterative clustering with Euclid distance and correlation was adopted to obtain the major controlling factors including TOC, porosity, quartz content and pyrite content. On this basis, a stepwise regression method was used to formulate the fitting equation for the correlation between gas content and these determined major controlling factors, which was also validated and found to be in consistent with the data from other well cores and outcrop samples. With this proposed correlation method, the shale gas in place in this study area is calculated to be 1.77 trillion m3, indicating that the study area is prosperous for future shale gas exploration and development.

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