Hydrocarbon geochemistry and charging history of the deep tight sandstone reservoirs in the Dabei Gas Field, Kuqa Depression, Tarim Basin, NW China

Abstract

The geochemical feature and evolutionary history of hydrocarbons from the deep Cretaceous Bashijiqike (K1 bs) Formation tight sandstone reservoir in the Dabei Gas Field, Kuqa Depression were investigated using gas chromatography, gas chromatography–mass spectrometry, inclusions petrography and micro-thermometry, laser Raman spectroscopy, and quantitative grain fluorescence. The result indicates that natural gases from the deep sandstone reservoir are mainly composed of alkanes and belong to dry gases, of which methane accounts for 94.30–97.20% (avg. 95.64%), and ethane is 1.23–2.45% (avg. 1.95%). The stable carbon isotopic value of methane and ethane is −31.9‰ to −29.3‰ (avg. −30.3‰) and −24.2‰ to −19.4‰ (avg. −21.7‰), respectively, and this reflects the features of high-mature coal-derived gases. In addition, natural gases in the Dabei Gas Field have characteristics of coal-derived gases which were sourced from Jurassic coal measures. Oils in the Dabei Gas Field predominately originated from Triassic Huangshanjie (T3 h) Formation mudstones with some contributions from Jurassic coaly rocks. Petrological and micro-thermometry results of fluid inclusions suggest that the K1 bs Formation tight sandstone reservoirs have experienced two phases of hydrocarbons charge histories, namely “early oil and later gas.” The quantitative grain fluorescence analysis indicated that sandstone samples with quantitative grain fluorescence index value >5 and quantitative grain fluorescence-extraction intensity >40 pc in Wells DB101 and DB2 can be used as indicators for the paleo oil layers or the migration channels of later charged natural gas. The aforementioned analyses and burial and thermal histories of K1 bs sandstone reservoir demonstrated that oil charged at 10 Ma and natural gas charged at approximately 3 Ma in the study area. Furthermore, paleo-tectonic evolution enabled source rocks to mature and expel hydrocarbons, and the structurally related faults and traps provided pathways and places for hydrocarbon migration and accumulation.

The geochemical differences and origin of multilayered natural gases in marine strata, the northwestern Sichuan Basin, China

“…Almost half of gas samples of JLS show a reversal of methane and ethane carbon isotopes (Table 2; Figure 12). According to previous scholars reported, five probably reasons for carbon isotopes reversal are as follows (Dai et al, 2014;Wei et al, 2019), (1) mixing of organic and inorganic natural gas; (2) natural gas sourced from various rocks or generated from same source but at various periods; (3) mixing of oil-associated gas and coal-derived gas; (4) primary or secondary microbial natural gas; and (5) natural gas generated under high temperature and pressure conditions. The burial depth of Middle and Upper Permian source rocks (P 2 m-P 2 q, P 3 w, and P 3 d ) is beyond 7000 m, resulting in high pressure and temperature conditions causing natural gas to reach overmature stage.…”

A reservoir quality evaluation approach for tight sandstone reservoirs based on the gray correlation algorithm: A case study of the Chang 6 layer in the W area of the as oilfield, Ordos Basin

“…Tight oil exploration has made a series of new discoveries and breakthroughs in the Ordos Basin (Zhou et al, 2020), Sichuan Basin (Guo et al, 2018), Songliao Basin (Xi et al, 2018), Junggar Basin, Tarim Basin (Wei et al, 2020), etc., with rapid growth of reserves and production (Zheng et al, 2017). The Ordos Basin is one of the main production areas of tight oil and gas in China.…”

“…With continuous progress in oil and gas exploration and development theory, domestic and international oil and gas exploration and development have gradually developed from conventional to unconventional resources (Aguilera, 2018;Guo et al, 2018;Liu et al, 2019a;Stephen et al, 2020;Wang et al, 2015). Meanwhile, the world's oil and gas exploration and development turn to deeper, more complex and more challenging unconventional oil and gas fields with more complex enhanced oil and gas recovery approaches than those applied to conventional sources (Liu et al, 2019b(Liu et al, , 2020Wei et al, 2020;Zhang et al, 2020;Zhong et al, 2020).…”