Distribution and Geochemical Characteristics of Fluids in Ordovician Marine Carbonate Reservoirs of the Tahe Oilfield

• Published in: Journal of earth science (Wuhan, China) China), 2014-06, Vol.25 (3), p.486-494
• Main Authors: Li, Mei, Lou, Zhanghua, Zhu, Rong, Jin, Aimin, Ye, Ying
• Format: Article
• Language: English
• Subjects: Biogeosciences; Calcite; Carbonates; Connate water; Crude oil; Deuterium; Earth and Environmental Science; Earth science; Earth Sciences; Fluid dynamics; Fluid flow; Fluids; Geochemistry; Geology; Geotechnical Engineering & Applied Earth Sciences; Karst; Meteoric water; Meteoric waters; Oil and gas fields; Oil field equipment; Oil-water interface; Oilfield equipment & services; Ordovician; Pore water; Reservoirs; Vertical distribution; Water content; Water flow; 储层分布; 含油饱和度; 地球化学特征; 塔河油田; 奥陶系油藏; 流体分布; 海相碳酸盐岩; 碳酸盐岩储层
• ISSN: 1674-487X; 1867-111X
• DOI: 10.1007/s12583-014-0453-3

The Ordovician carbonate reservoirs in the Tahe Oilfield are highly heterogeneous, which have undergone multiple superimposed transformations by tectonic activities and karst processes, leading to an extremely complex fluid distribution. The geochemical characteristics of geofluids also display great disparities. Results show that the vertical distribution of oil and gas are continuous, however the oil-water interfaces in different blocks of the Tahe Ordovician Oilfield are numerous. Meteoric water infiltration is regarded as the main reason for the high oil-water interface and high water content to the north of Tahe Oilfield, especially in well blocks S78–S73. The isotopic values of deuterium-oxygen in the groundwater and carbon-oxygen from calcite veins confirm that formation water in Ordovician reservoirs of the Tahe Oilfield was a mix of meteoric water and connate water, and the proportion of meteoric water gradually increases from south to north, while connate water decreases. The Tahe Ordovician reservoirs are characterised by multiple hydrocarbon charges, and the general migrating direction is from southeast to northwest and from east to west. High production could be obtained in the northern area of the Tahe Oilfield since the oil layers are thick and oil is highly saturated. The residual water within the reservoirs is low, and heavy oil is dominant in this area. Only a small amount of pore water has been replaced by oil in the southern Tahe Oilfield, leading to low oil saturation and a high content of residual water. Crude oil is herein mainly of medium-light type. During the process of exploration in this region, acid fracturing reformation is usually required for wells to increase their output; however the yield is still low.