Abstract
The characteristics of the Lower Qiulitage Group in Bachu uplift, which originated in the Upper Cambrian period, are not clear. Based on four core observations, identification of 40 thin sections, and geochemical analysis of samples, this study concludes that crystal dolomite reservoirs developed in the Lower Qiulitage Group in Bachu uplift. Intercrystalline pores and dissolved pores formed the main reservoir space, while dissolution pores and fractures were developed in the middle and bottom part of the formation. The reservoir features low porosity and low permeability, and the fine-medium crystalline dolomite reservoir has the best pore structure. According to a petrochemical analysis, the Lower Qiulitage Group reservoir experienced intense dolomitization, with slightly higher content of trace elements Mn and Sr and negative oxygen isotropy. Tectonic hydrothermal dolomitization developed locally under the influence of base faults, and vug pores were filled with saddle dolomites and siliceous filling. The presence of rare earth elements Ce and Eu presented positive anomaly characteristics. It suggested that the CO2 acid dissolution caused by hydrothermal fluids may be a new mechanism for the increase in pores in deeply buried reservoirs, which is worth further study.
Highlights
With the development of oil and gas exploration in the Tarim Basin, researchers have increasingly focused on the prospect of dolostone in the upper Cambrian salt in the Bachu uplift (He, 2013; Yang, Liu, Tian, Wanbin & Zhu, 2011; Jiao et al, 2011; Cai, Li, Quian & Zhang, 2010; Chen, Wang, Meng & Zheng, 2002)
Many gas logging anomalies appeared in the HT1, BT5, MB1, and T1 wells drilled by the Lower Qiulitage Group in the upper Cambrian system (Fig. 1), indicating that the Lower Qiulitage Group reservoir could be well developed (Huang, Jiang & Ma, 2014; Zhu, Meng, Jin, Liu & Hu, 2015; Cai, Mao, Qian, Chen & You, 2009)
The reservoir characteristics and genetic model of the Lower Qiulitage Group are studied through core observation and petrochemical analysis of the upper Cambrian samples, to provide theoretical support for further risk exploration in the Bachu uplift
Summary
With the development of oil and gas exploration in the Tarim Basin, researchers have increasingly focused on the prospect of dolostone in the upper Cambrian salt in the Bachu uplift (He, 2013; Yang, Liu, Tian, Wanbin & Zhu, 2011; Jiao et al, 2011; Cai, Li, Quian & Zhang, 2010; Chen, Wang, Meng & Zheng, 2002). The fracture was mostly filled with dolomite and organic matter (Fig. 3b), and needle pores were formed by later dissolution on the core. The medium-coarse crystalline dolomites were mainly developed in Well T1 and BT5 in the west Bachu uplift, mostly with anhedral-subhedral form. The fine dolomite with higher euhedral was distributed in the dissolution pores, or at the edge of the fracture, and the intercrystalline pores and dissolved pores are relatively developed. The fine dolomite reservoir had higher porosity and a better pore-permeability relationship according to the crystal type (Fig. 4b). The statistics of the dissolved pores of the Lower Qiulitage Group showed that the distribution of reservoir space was heterogeneous (Fig. 6), mainly composed of dissolved pores and fractures. The wells of Fang and HT1 are characterized by dissolved pores and mainly dominated by small vugs
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
