The Research and Application of a New Interpretation Chart—Taking the Ordovician Majiagou Formation in the Eastern Ordos Basin as an Example

Abstract

The weathering crust reservoir in the upper ordovician majiagou formation in the eastern ordos basin have been focused as a desert of exploration in recent years. As a result of uplift in Caledonian, reservoir spaces such as fractures and pores in the majiagou formation in the eastern part of the basin were mostly filled and destroyed, all above cause the worse conjunction and higher heterogeneity. Generally, due to the low porosity and permeability, the nature gas saturation of Majiagou formation is so low that the response of logging parameters while drilling besides gas logging is too weak to detect. For instance, the logging gas measurement value is often less than 1%, even using the drilling fluid lower than 1.20 g/cm3, which makes it difficult to identify the reservoir fluid properties by traditional methods in this case. Therefore, it is imperative to modeling a new method based on the existing geological data. The long-term observation shows that compared with the value of gas logging, the gas measurement curve with complete shape which contains peak, stable and fall appears to have a stronger correlation between the peak shape and the fluid properties. In this paper, the researchers try to quantify the analysis of gas measurement patterns, and the studies based on gas logging peak morphological elements elements which includes the stability of the gas peak, the towing phenomenon of the slow drop, the speed and amplitude of the rise or fall. At last, the relationship between gas peak formation and fluid properties is confirmed by a large number of statistics and comparisons. On the basis of the results above, a new interpretation method for fluid analyzing is proposed. The trait of single gas cruve peak could be summarized into kurtosis and skewness by the interpretation method of illustration, and the different types of reservoirs are respectively placed into the two-dimensional coordinate box with kurtosis as the X-axis and its skewness as the Y-axis, so as to establish a reservoir interpretation method based on kurtosis - skewness plate. In the Majiagou formation in the east of ordos basin, it has been taken a mount of application, which has achieved better result with the average interpretation coincidence rate more than 71%. In addition, it is noteworthy that the accuracy of the plate method for identifying gas layer is over 82% by more than 50 wells applications.KeywordGas interpretation chartOrdos basinMajiagou formationFluid interpretation