Logging Identification and Evaluation Method for Bitumen-Bearing Reservoirs

Bitumen, as a hydrocarbon with high density and poor fluidity, filling the reservoir’s pores and throats, affects the reservoir’s physical properties and productivity. Bitumen and oil and gas share similar characteristics in terms of logging response, specifically an increase in logging resistivity. This similarity can lead to the mistaken interpretation of bitumen, which occupies the pore space, as oil and gas during logging analysis. As a result, the reservoir’s effective porosity and oil saturation may be overestimated, and certain layers may be incorrectly identified as containing oil and gas. The reservoir’s effective porosity and oil saturation will be misinterpreted as being larger, and the strata will be misinterpreted as oil- and gas-bearing. On the basis of a large number of core observations and thin layer analysis, the logging response characteristics of bitumen-developed reservoir were summarized to qualitatively identify bitumen-bearing reservoir. Based on conventional and NMR logging data, the difference method between conventional logging NPR was established to accurately and quantitatively calculate the bitumen content in the reservoir. Due to its affection on effective porosity and resistivity of bitumen-bearing reservoir, bitumen’s influence was excluded before using Alchi formula to calculate the water saturation. This logging and evaluation method for bitumen-bearing reservoir has important significance for guiding the efficient field development.