Oil & Gas Geology ›› 2013, Vol. 34 ›› Issue (5): 685-693.doi: 10.11743/ogg20130516

• Sequences and Reservoirs • Previous Articles     Next Articles

Sedimentation and diagenesis of Chang 82 reservoir in the Yanchang Formation in Jiyuan region, Ordos Basin

Chen Zhaobing1,2, Zhu Yushuang1, Chen Xinjing3, Niu Xiaobing4, Zhou Shuxun5, Wang Xiujuan5, Zhao Aibing5   

  1. 1. State Key Laboratory of Continental Dynamics, Geology Department of Northwest University, Xi'an, Shaanxi 710069, China;
    2. No. 2 Gas Production Plant, PetroChina Changqing Oilfield Company, Xi'an, Shaanxi 710200, China;
    3. No. 6 Oil Production Plant, PetroChina Changqing Oilfield Company, Xi'an, Shaanxi 710200, China;
    4. Research Instituie of Petroleum Exploration and Development, PetroChina Changqing Oilfield Company, Xi'an, Shaanxi 710021, China;
    5. Reservoir Evaluation Office, PetroChina Changqing Oilfield Company, Xi'an, Shaanxi 710021, China
  • Received:2013-02-04 Revised:2013-08-20 Online:2013-10-08 Published:2013-10-08

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Abstract:

The structure of Jiyuan region in the Ordos Basin was relatively stable during the deposition of Chang 82.In this period,a shallow water delta depositional system was developed,the lake shore line slightly migrated in the southeast,and distributary channel and underwater distributary channel constituted the deposition framework.This paper studied the diagenesis of Chang 82 reservoir based on large amount of thin sections,core observation,SEM samples,X-ray analysis,and Cathodoluminescence analysis.The study shows that the diagenesis has double effects on the reservoir.On one hand,early development of chlorite film has a positive effect on anti-compaction.The early calcite is easy to be dissolved by organic acid,resulting in secondary pores and improving poroperm characteristics.Dissolution is the major mechanism of secondary pore formation and can greatly improve reservoir poroperm characteristics.On the other hand,compaction destroys the primary porosity formed in early digenetic process,and late ferrocalcite fills pores,resulting in local strong calcareous cementation zone.In general,the sedimentary facies and diagenetic facies control the distribution of oil and gas.The former determines the reservoir shape and dimensions.While the later modifies reservoir pore space.Late diagenesis-modified chlorite-cemented sedimentary facies with residual inter-granular pores and that with feldspar-dissolution plus residual inter-granular pores are the major reservoir spaces for hydrocarbon accumulation.

Key words: diagenetic facies, sedimentation and diagenesis, shallow water delta, Yanchang Formation, Ordos Basin

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