Methods for shale gas play assessment: A comparison between Silurian Longmaxi shale and Mississippian Barnett shale

Abstract

Based on field work, organic geochemical analyses and experimental testing, a six-property assessment method for shale gas is proposed. These six properties include organic matter properies, lithofacies, petrophysical properties, gas content, brittleness and local stress field. Due to the features of continuous distribution over a large area and low resource abundance in shale plays, a sweet spot should have these following properties: (a) TOC>2%; (b) brittle minerals content (>40%) and clay minerals (<30%); (c) Ro (>1.1%); (d) porosity (>2%) and permeability (>0.000 1 mD), and (e) effective thickness (30-50 m). Applying these criteria in the Sichuan Basin, the Silurian Longmaxi shale consists of four prospecting sweet spots, including blocks of Changning, Weiyuan, Zhaotong and Fushun-Yongchuan. Although these four blocks have some similarities, different features were usually observed. After comprehensive analyses using the six-property assessment method, the Fushun-Yongan Block ranks the most favorable sweet spot, followed by the Weiyuan Block. For the other two blocks, the Changning Block is better than the Zhaotong Block. By comparing with the Mississippian Barnett shale, characteristics that are crucial for a high-yielding in the Sichuan Basin include a high content of organic matter (TOC>2.5%), a moderate thermal maturity (Ro=0.4%-2%), a high content of brittle minerals (quartz: 30%-45%), a high gas content (>2.5 m 3 t -1 ), and types I and II 1 kerogen. KEY WORDS: shale gas play, Silurian Longmaxi shale, Barnett shale, sweet spot, six-property assessment.

Fault reactivation and earthquakes with magnitudes of up to Mw4.7 induced by shale-gas hydraulic fracturing in Sichuan Basin, China

“…Another relationship, M W = 1.89log 10 A − 5.88, was found to work for microseismicity ( M W < 0) caused by hydraulic fracture opening in shale formations 32 . The shale formation thickness in the Shangluo site is approximately 40−60 m 33 , 34 . In fact, microseismic events caused by hydraulic fracture opening have a magnitude less than −1 in the Sichuan Basin 27 – 29 .…”

Geochemistry, Paleoenvironment and Mechanism of Organic‐Matter Enrichment in the Lower Silurian Longmaxi Formation Shale in the Sichuan Basin, China

“…The data for YS12 were provided by the current study's experimental analyses and well logs. A Dai et al, 2014;, Zou et al, 2015Guo and Zhang, 2014). total of 19 LLF shale core samples from the YS12 Well were analyzed for total organic carbon (TOC) and major and trace elements.…”

“…Many microfossils, such as foraminiferas, sponge spicules, and radiolarians, are observed in the Longmaxi Formation shale (Zhang et al, 2012;Guo and Zhang, 2014;Li et al, 2016) and the Barnett Shale (Loucks and Ruppel, 2007;Pan et al, 2015), especially in organic-rich layers. Previous studies have suggested that biogenic silica is an important component of the siliceous component of marine shale (Ross and Bustin, 2009;Zhao et al, 2016).…”

H2O2-Enhanced Shale Gas Recovery under Different Thermal Conditions

“…The total organic matter (TOC), including volatile matter (VM) and fixed carbon (FC), is 10.82% and the carbon content is about 6.24%. Table 2 gives exinite, vitrinite, and inertinite weight percentages of the shale sample and vitrinite-like macerals reflectance (Ro) which can be used to evaluate the thermal maturity of shale [25]. The Ro value is 1.85 and the organic matter type of this shale is type II.…”