Vitrinite Equivalent Reflectance Estimation from Improved Maturity Indicator and Well Logs Based on Statistical Methods

Abstract

Estimation and correct determination of vitrinite equivalent reflectance in rock is crucial for the assessment of the source rock in both conventional and unconventional hydrocarbon deposits. These parameters can be determined in laboratories on rock samples. Laboratory measurements provide only point information. However, the use of well logs could overcome discontinuities in the data and provide parameters throughout a study interval. Attention has been paid to the estimation of TOC based on well logs. Vitrinite equivalent reflectance estimation is less well discussed and most papers reported cases with high TOC content in analyzed deposits. In this paper, the estimation of improved Ro is presented using a calculated maturity indicator with well logs. As the organic matter content is not high, additional steps were required for the calculation. To improve the quality of the fit and to find similar intervals, the data were grouped using cluster and neural network analysis. The next step was to use the resistivity log to improve the obtained maturity indicator. Due to the changing properties of kerogen with the type and degree of thermal maturity, this approach turned out to be reliable. The use of resistivity significantly increased the correlation coefficient and reduced errors. The method was tested on two wells with different type and maturity of kerogen. The obtained results are satisfactory, which makes it possible to use the method even in formations with a low organic matter content.

Use of Cluster Analysis to Group Organic Shale Gas Rocks by Hydrocarbon Generation Zones

“…One such parameter is to determine optimal (in terms of the effective grouping process)values of maximum distances between objects (in this case samples) that must be maintained in order for the samples to be qualified to the same window. The method used is complementary to the work of other scientists involved in research on the classification of rock samples based on kerogen maturity [16,[45][46][47][48]. Funding: This article is the result of research conducted in connection with the project: Selection of optimal methods for estimation of resources and (geological and commercial) risk at prospecting stage in relation to unconventional 'shale gas', 'shale oil', and 'tight gas' deposits in Poland, and development of methods for documentation of unconventional deposits, co-funded by the National Center for Research and Development as part of the programme BLUE GAS-POLISH SHALE GAS.…”