Application of the geochemical prospecting to improve oilfield structure models

Abstract

Background: Complicated structure of surveyed area has minor efficiency of seismic surveys--the main method for petroleum and gas prospecting and interpretation of subsurface structure of the Earth. This paper gives an example that in certain cases geochemical surveys can be used as additional tool to establish suitable geological model of the trap. This paper presents geochemical studies in the southeastern part of European territory of Russia--Nagumanovskoe oilfield. Complicated geological structure causes difficulties to create suitable geological model of the trap itself. There are two models of geological structure for the Nagumanovskoe oilfield: Variant A: Researchers assume the presence of gas condensate accumulation and perspective for exploration traps, Variant B: Researchers assume presence of 2 local structures. Method and results: Geochemical data came from over than 2000 shallow probes (2 meters, 6.6 feet) of soil gas samples collected every 200 meters over more than 7 different long profiles. The adsorbed soil gases were analyzed for hydrocarbones. All samples were decomposed into geochemical populations. According to geochemical data the Nagumanovskoe oilfleld was well defined on all geochemical profiles. Examination and comparison of hydrocarbon ratio plots and magnitude graphs for each of the two models indicate that the more anomalous magnitude sites agree with the disposition of structures according to model B. The geochemical oil/gas data exhibit clearly defined compositional sub-populations which match the composition of the underlying reservoirs, difference in standard deviation of hydrocarbon values at background and Cretaceous structure (model B) leads to the deduction that variant B is more suitable geological structure model of the Nagumanovskoe oilfield. This example shows the use of geochemical surveys as additional tool for interpretation of underground struc~tres of the Earth.