TIAN Wen1, CHEN Gang1, LI Wenhou1, GAO Luheng2, YANG Fu3,4, BAI Jinli1, CHEN Meng1
(1. State Key Laboratory of Continental Dynamics, Department of Geology, (Northwest University), Xi'an 710069, China;
2. Yanchang Petroleum (Group) Co., Ltd, Xi’an 710069, China;
3. Key Lab of coal Resources Exploration and Comprehensive Utilization, MLR, Xi'an 710069, China;
4. Shaanxi Coal Geology Group Co., LTD, Xi'an 710069, China)
Abstract: The Ma56th member of Bahannao area in the north of the Ordos Basin is an important oil and gas reservoir; it is weathering crust type carbonate formation, the main lithologic being oolitic limestone and grain dolomite, secondary pore development. By using Finnigan MAT252 gas isotope ratio mass spectrometry, the carbon and oxygen isotope were determined. This article also analyzes the diagenetic environment and porosity evolution conditions for carbonate formation in Bahannao area. Results show that compared with the Ordovician, burial dolomitization environment of high temperature led to the water’s δ18O value obviously negative, and dolomite’s δ18O value negative compared with limestone’s δ18O value. The δ13C value is considerable with Ordovician water’s δ13C value with very few numerical biased. Results reveal that the Ma56th member is less influenced by organic carbon in the process of diagenesis, and diagenesis occurred under shallow-buried conditions. The transformation of atmospheric freshwater diagenetic optimize porosity and seepage channel, improved reservoir physical properties, and making the relation between the porosity and permeability of the study area obvious.
Keywords: carbonates; carbon and oxygen isotopes; secondary pore; dolomitization
Email: chengang@nwu.edu.cn
ACTA MINERALOGICA SINICA Vol. 36, No. 1, 2016, Page 12-18
