Using the Modified Resistivity–Porosity Cross Plot Method to Identify Formation Fluid Types in Tight Sandstone with Variable Water Salinity

Abstract

It is generally difficult to identify fluid types in low-porosity and low-permeability reservoirs, and the Chang 8 Member in the Ordos Basin is a typical example. In the Chang 8 Member of Yanchang Formation in the Zhenyuan area of Ordos Basin, affected by lithology and physical properties, the resistivity of the oil layer and water layer are close, which brings great difficulties to fluid type identification. In this paper, we first analyzed the geological and petrophysical characteristics of the study area, and found that high clay content is one of the reasons for the low-resistivity oil pay layer. Then, the formation water types and characteristics of formation water salinity were studied. The water type was mainly CaCl2, and formation water salinity had a great difference in the study area ranging from 7510 ppm to 72,590 ppm, which is the main cause of the low-resistivity oil pay layer. According to the reservoir fluid logging response characteristics, the water saturation boundary of the oil layer, oil–water layer and water layer were determined to be 30%, 65% and 80%, respectively. We modified the traditional resistivity–porosity cross plot method based on Archie’s equations, and established three basic plates with variable formation water salinity, respectively. The above method was used to identify the fluid types of the reservoirs, and the application results indicate that the modified method agrees well with the perforation test data, which can effectively improve the accuracy of fluid identification. The accuracy of the plate is 88.1%. The findings of this study can help for a better understanding of fluid identification and formation evaluation.

Identification Analysis of Fluid Type in the Low Resistivity Zone of Well Z-2 Field "Z", South Sumatera

“…Determination of the type of fluid at low resistivity and low contrast determines the fluid contained in the reservoir with the phenomenon of low resistivity low contrast. In a study conducted by Yang, et al 2021 entitled "Using the modified Resistivity-porosity cross plot method to identify formation fluid type in tight sandstone with variable water salinity." They conducted an analysis of the type of fluid contained in the low resistivity low contrast zone using a cross plot between porosity and resistivity parameters which can be seen in Figure 1 [15].…”

Genetic mechanisms and multi-parameter logging identification of low-resistivity oil pay: A case study of the Triassic Chang 6 member, Zhidan area, Ordos Basin, China

“…The total oil resources in the basin are about 8.6 billion tons, ranking fourth in the China. [20][21][22][23][24] After years of exploration and research, it has been found that the Triassic Yanchang Formation reservoirs in Dingbian, Jiyuan, Huanxian, Ansai and other areas in the basin contain abundant low-resistivity oil and gas resources. 25 ， 26 The Yanchang Formation reservoir has complex pore structure, low permeability, and the growth of low-resistivity oil pays, which has brought great obstacles to exploration and development.…”

Capturing synchronization with complexity measure of ordinal pattern transition network constructed by crossplot

“…With the in-depth study and application of statistical analysis and complex network theory, crossplot [28][29][30] and ordinal pattern transition networks (OPTN) [31][32][33][34] are emerging as major tools for nonlinear time series interrelationship analysis and are finding meaningful applications in the analysis of experimental data in a variety of research fields. Crossplot is a graphical representation of time series in the Cartesian plane.…”