Use of probabilistic and statistical methods for separation of rocks into permeable and impermeable parts (on example of clastic deposits of Visean stage of Sofyinskoe field)

Abstract

Separation of well section into permeable and impermeable parts is one of the main problems for further construction of a geological model, reserves estimation and field development planning. Quality of separation depends on amount of knowledge about geological section, level of theoretical development of well logging methods and general geophysical characteristics of the area. The fullest differentiation is obtained by using a complex of geological and geophysical methods. The paper is focused on Visean deposits of well of Sofyinskoe field drilled in 2014. A complex of activities was performed along with well logging. Porosity was calculated by acoustic and neutron logging. Core analysis was performed. Using well logging and results of core analysis selection was made, used for construction of statistical models. Based on statistical models all parameters were made-up to a single measurement system. The analysis of degree of influence of geological and geophysical parameters was made. The geological analysis shows that the greatest influence belongs to porosity and residual water. The geophysical analysis shows that the greatest influence belongs to hydrogen content and own radioactivity of rocks. A complex probabilistic parameter that includes all measurements according to core and geophysical parameters is calculated. Results of core analysis are considered fully in order to obtain a highest degree of difference. Almost all the parameters of geophysical data increase the degree of difference, except for lateral logging, microgradient and micropotential tools and transit time of P-wave for short tool, which reduces the degree of difference. Based on values of a complex parameter that have maximum differences in geological and geophysical parameters, relationships of geological and geophysical parameters were built. Scatter charts show that fields of measured points are not intersected, which confirms a correct separation of a section. Using a statistical method allows to consider fully available geological and geophysical data to separate a section into permeable and impermeable parts.

Keywords

• well
• separation of well section
• reservoir
• seal rock
• open porosity
• irreducible water saturation
• hydrogen content
• natural radioactivity
• well logging methods
• core studies
• Visean oil and gas complex
• linear models
• statistical probability
• mathematical statistics
• scatter chart
• Student's coefficient
• integrated probability