Origin, Migration, and Accumulation of Carbon Dioxide in the East Changde Gas Field, Songliao Basin, Northeastern China
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Petroleum Science (2018) 15:695–708 https://doi.org/10.1007/s12182-018-0259-5 (0123456789().,-volV)(0123456789().,-volV) ORIGINAL PAPER Origin, migration, and accumulation of carbon dioxide in the East Changde Gas Field, Songliao Basin, northeastern China 1 2,3 4 3 3 1 Yu-Ming Liu • Yue Dong • Zhen-Hua Rui • Xue-Song Lu • Xin-Mao Zhou • Li-Chun Wei Received: 21 August 2017 / Published online: 16 October 2018 Ó The Author(s) 2018 Abstract CO2 reservoirs are widely distributed within the Yingcheng Formation in the Songliao Basin, but the extreme horizontal heterogeneity of CO2 content causes difficulties in the exploration and exploitation of methane. Former studies have fully covered the lithology, structure, and distribution of the reservoirs high in CO2 content, but few are reported about migration and accumulation of CO2. Using the East Changde Gas Field as an example, we studied the accumulation mechanisms of CO2 gas. Two original types of accumulation model are proposed in this study. The fault-controlled accumulation model refers to gas accumulation in the reservoir body that is cut by a basement fault (the West Xu Fault), allowing the hydrocarbon gas generated in the lower formation to migrate into the reservoir body through the fault, which results in a relatively lower CO2 content. The volcanic conduit-controlled accumulation model refers to a reservoir body that is not cut by the basement fault, which prevents the hydrocarbon gas from being mixed in and leads to higher CO2 contents. This conclusion provides useful theories for prediction of CO2 distribution in similar basins and reservoirs. Keywords Carbon dioxide reservoir Á Mantle-derived CO2 Á Faults Á Reservoir formation mechanism Á East Changde Gas Field Á Songliao Basin 1 Introduction also been accidentally discovered during natural gas exploration over the past two decades (Xu et al. 1995; Sun The Songliao Basin is a Mesozoic–Cenozoic basin located et al. 2009; Guo et al. 2017a, b). These CO2 reservoirs are in northeastern China that contains abundant oil and gas located within a narrow strip within the Xujiaweizi resources. Several billion tonnes of oil have been discov- Depression, the Changling Depression, and the Wanjinta ered in the basin’s oil fields since exploration began in Depression. However, CO2 accumulation has an extremely 1950. However, in addition to the large amount of hydro- heterogeneous horizontal distribution. The difference in the carbon gas, a number of CO2 reservoirs, whose CO2 con- CO2 content of two wells located less than 1 km apart can centrations vary significantly from \ 30 to [ 98%, have be as much as 70%. For example, the Changde area in the Xujiaweizi Depression has a complex gas genesis, with both organic gas (methane) and inorganic gas (CO2). Edited by Jie Hao Reservoirs with CO2 contents[ 84% have been discovered & Yu-Ming Liu in the volcanic reservoirs, e.g., in wells Fs9 and Fs701 in [email protected] the Yingcheng Formation in East Changde. Whereas, in & Zhen-Hua Rui wells Fs7 and Fs6, located less than 3 km away, the CO2 [email protected] content is 15%–40%. This phenomenon has resulted in a great deal of interest in the genesis of CO and the reservoir 1 2 College of Geosciences, China University of Petroleum, formation process in the Songliao Basin (Yang et al. 2011; Beijing 102249, China Fu and Song 2005; Shao et al. 2000; Qu et al. 2016;Xu 2 School of Energy Resources, China University of et al. 1999; Dai 1996;Du2005; Guan 1990; Zhang et al. Geosciences, Beijing 100083, China 2009; Li et al. 2006; Guo et al. 2000; Yu et al. 2010; Cao 3 Research Institute of Petroleum Exploration and 1996; Rui et al. 2018a, b). Most scholars agree that the CO Development, CNPC, Beijing 100083, China 2 in the Songliao Basin is inorganic and mantle-derived 4 Independent Project Association, Inc., Leesburg, USA 123 696 Petroleum Science (2018) 15:695–708 according to the isotopic composition of the CO2.Itis It has undergone widespread deposition of Cretaceous– generally accepted that mantle fluids, especially basaltic Quaternary strata with a structure characterized by faults at magmas, contain significant amounts of volatiles, such as the bottom and depressions at the top. Three structural CO2,H2O, and He. When the temperature decreases as layers can be identified: a fault-depressed structural layer, a upwelling occurs, the magma will degas, and these vola- depressed structural layer, and an inverted structural layer. tiles will continuously migrate through fractures and pores, During the past decade, several CO2 reservoirs or CO2- and can be trapped in CO2 reservoirs under the appropriate containing reservoirs (fields) have been accidentally dis- conditions. This is how mantle-derived CO2 reservoirs covered during natural gas exploration in the Songliao form (Yang et al. 2011). However, previous studies have Basin. Currently, there are multiple high CO2-content failed to produce a reasonable explanation for the differ- reservoirs and gas seepages, such as the CO2 gas seepages ences in the CO2 contents of reservoirs that are located in the Five Connected Ponds on the north edge of the basin fairly close together. Several scholars have proposed a self- and the high CO2-content middle-shallow sand-conglom- generating and self-preserving reservoir formation model. erate reservoirs located in the Wanjinta, Gudian, Qian’an, They argue that the CO2 in the Songliao Basin is derived and Honggang Depressions. A number of CO2 reservoirs from magmas associated with Cretaceous volcanic activity. and gas spots in the volcanic reservoirs of the Yingcheng The CO2 degassed from these magmas due to decreasing Formation were also recently discovered by deep explo- temperatures when the magma cooled, and it was stored ration, such as the Fangshen 9 (CO2 content = 84.2%– in situ forming reservoirs (Liu et al. 2005; Tan et al. 2005). 90.4%), Xushen (CO2 content = 24%), Xushen 10 (CO2 According to this theory, there should be widespread CO2 content = 90%), Xushen 19 (CO2 content = 93%), Xushen reservoirs in the Songliao Basin wherever Cretaceous 28 (CO2 content = 80.7%), and Dashen 2 (CO2 con- volcanic rocks are located. However, the CO2-containing tent = 32%) in the Xujiaweizi Depression, East Changde, reservoirs have a limited distribution—they are mainly in the northern part of the Songliao Basin (Lu et al. 2005, located where faults intersect (Guo et al. 2000; Yu et al. 2008; He et al. 2005) (Fig. 1). Thus, it can be concluded 2010; Zeng et al. 2017). Due to the fact that the density of that CO2 is widely, but unevenly, distributed in the Son- CO2 is greater than that of hydrocarbon gases, several gliao Basin. The absence of well-established conditions for scholars proposed the ‘‘gravitational differentiation’’ industrial utilization and treatment of this CO2 has made it reservoir formation model, which concludes that gravity riskier and more difficult to explore and exploit the asso- caused CO2 to accumulate at the bottom of reservoirs and ciated hydrocarbon gases. hydrocarbon gases at the top (Lin et al. 2010; Wei et al. 2009). However, there is little difference between the density of CO2 and the densities of methane and ethane. 2.1 Structural characteristics Therefore, whether such a small density difference can lead to such a significant difference in the horizontal distribu- Tectonically, the Changde area is located in the western tion of CO2 needs to be investigated further. slope in the Xujiaweizi Depression (Fig. 1). From a In this study, several typical reservoirs in East Changde regional perspective, the western region is undergoing were selected to investigate the genesis of CO2 using core basement uplift and is split into a northern half and a data gas samples, temperature, pressure, and seismic data. southern half by the ancient valley running along Chang Based on this data, the distribution characteristics of vol- wells 101–102. Situated in the depression in the eastern canic reservoirs and basement faults are discussed, and a part of the basement uplift, the East Changde Gas Field is a CO2 migration and reservoir formation model for East syncline structure trending northwest with a depth of up to Changde is explored in order to analyze the factors gov- 4100 m. This syncline is characterized by simple structural erning CO2 distribution in the Songliao Basin. features and some topographic highs. The sedimentary strata pinch out to the west above the basement uplift. The East Changde Gas Field is located in the western part of the 2 Geological setting Xujiaweizi Depression (Figs. 1, 2) where reservoirs are developed in the volcanic reservoir bodies in the Lower The Songliao Basin is the largest Mesozoic–Cenozoic Cretaceous Yingcheng Formation. continental basin in northeastern China. It is 750 km long, There is a 2–6 km, NNE-trending fault with a fault 330–370 km wide, and covers an area of nearly displacement of 40–100 m located in the syncline area of 255,000 km2, extending from north to south through Hei- the northern part of the East Changde Gas Field. This is a longjiang Province, Jilin Province, and Liaoning Province long-lived normal fault that separates the Qingshankou (Fig. 1). The Songliao Basin has experienced three phases Formation hanging wall and the Shahezi Formation foot of evolution, i.e., rift, depression, and structural inversion. wall. A 1–2-km-long, NS-trending fault is located to the 123 Petroleum Science (2018) 15:695–708 697 N 10 km Songliao Basin Beijing Ds2 Sns2 East Changde Gas Field Ses1 B Ss1 Qiqihaer C101 Daqing C201 Fs6 Xs6 Xs22 Fs7 Xs1 B’ Xujiaweizi Fs5 Fs701 Ss2 Depression Haerbin Xs23 Fs4 Fs9 CC’Xs21 C401 Fs901 Xs28 Changchun Xs8 Xs3 Xs13 Xs901 Xs12 Xs10 Xs19 Ss1 Wells producing CO2 CO2 content Zs1 Zs12 Igneous body Proved reserves Survey line Faults 100% 80% 60% 40% 20% 0% Fig.