Genesis analysis and identification of low-resistivity contrast oil-bearing reservoirs: a case study in the Triassic Chang 3 Member of the Yanchang Formation in Pengyang Region, Southwestern Ordos Basin, China

In the southwestern Ordos Basin, the formation water salinity and resistivity of Jurassic sandstone reservoirs are characterized by rapid changes and great variations, which lead to difficulties in the identification of reservoir fluid types and in the development and exploration of hydrocarbons in this area. To explore appropriate methods for reservoir fluid identification provided with complex formation water salinity and resistivity, we conducted three research steps. Firstly, using formation water testing and well logging data, the formation water salinity, spontaneous potential, and reservoir resistivity were used to calculate the formation water resistivity. Secondly, the calculation results were used to separate reservoir fluid types. Thirdly, the calculated formation water resistivities were classified and the relationship of the formation water resistivity and oil-producing interval was established. The results showed that, for oil-producing intervals, the formation water resistivity calculated using the reservoir resistivity is the highest, while that using the formation water salinity is the lowest. Based on this understanding, two identification methods of reservoir fluid types were proposed, including the qualitative curve overlap method and the quantitative ternary graph method. The curve overlap method can be applied to visually distinguish reservoir fluid types through the differentiation of formation water resistivity. Compared with some earlier quantitative methods, the ternary graph method can achieve an efficiency of 87.7% in identifying the type of reservoir fluid. Finally, the reliability of both methods was verified by case studies.

show abstract

Influencing factors and identification method of low-resistivity pay zone in Jurassic, Huanxian area, Ordos Basin

Guo

Wang

et al. 2022

Interpretation

View full text Add to dashboard Cite

Huanxian area is in the west of the Ordos Basin and contains a widely distributed Jurassic low-resistivity pay zone. Due to the lack of a systematic summary of the influencing factors of the Jurassic low-resistivity pay zone in this location, oilfield engineers have not established a logging rapid identification method, increasing the complexity of oilfield exploration and development. Therefore, we reveal the main influencing factors and propose a corresponding logging identification method. Through a groundwater chemical composition test, phase permeability experiment, cast thin-section analysis, seismic data, and logging data, we have obtained the groundwater salinity, irreducible water saturation, clay mineral content, tectonic amplitude, and resistivity and apparent resistivity index of sandstone. The results of the correlation analysis indicated that the groundwater salinity is the main control factor for the development of the Jurassic low-resistivity pay zone in the study area, whereas other factors (such as irreducible water saturation) are secondary influencing factors. We have created a crossplot for groundwater salinity versus sandstone resistivity to identify the Jurassic low-resistivity pay zone based on clarifying the main control factor. The identification accuracy of this crossplot has reached approximately 65% through oil testing conclusions in the study area. To further improve the application, we have replaced sandstone resistivity with an apparent resistivity index in the crossplot. As a result, we have improved the identification accuracy of the Jurassic low-resistivity pay zone to more than 80%, which can meet the production demand. The results of this study can provide technical support for the exploration and development of the Jurassic low-resistivity pay zone, which is significant for optimizing various oil and gas resource production structures and coproduction methods in this location.

show abstract

Genesis analysis and identification of low-resistivity contrast oil-bearing reservoirs: a case study in the Triassic Chang 3 Member of the Yanchang Formation in Pengyang Region, Southwestern Ordos Basin, China

Cited by 4 publications

References 25 publications

Methods to identify near-source hydrocarbon-bearing potential reservoir using geophysical well logging data: A case study of the Triassic Chang 8 Formation in Pengyang Region, Southwestern Ordos Basin

Methods to identify near-source hydrocarbon-bearing potential reservoir using geophysical well logging data: A case study of the Triassic Chang 8 Formation in Pengyang Region, Southwestern Ordos Basin

Identification of an oil-bearing layer by formation water resistivity: A case study of the Jurassic reservoir, Southwest Ordos Basin

Influencing factors and identification method of low-resistivity pay zone in Jurassic, Huanxian area, Ordos Basin

Contact Info

Product

Resources

About