Genesis of solid bitumen

Hamed Sanei

doi:10.1038/s41598-020-72692-2

Abstract

This paper presents a new schematic model for generation and timing of multiple phases of solid bitumen throughout the continuum of organic matter maturation in source and tight reservoir rocks. Five distinct stages in the evolution of solid bitumen are proposed: (1) diagenetic solid bitumen (or degraded bituminite), which is not a secondary maceral resulting from the thermal cracking of kerogen. Instead it is derived from degradation of bituminite in the diagenesis stage (Ro < 0.5%); (2) initial-oil solid bitumen, is a consolidated form of early catagenetically generated bitumen at the incipient oil window (Ro ~ 0.5–0.7%); (3) primary-oil solid bitumen is derived from thermally generated bitumen and crude oil in the primary oil window (Ro ~ 0.7–1.0%); (4) late-oil solid bitumen (solid-wax) is derived from the waxy bitumen separated from the mature paraffinic heavy oil in the primary- and late-oil windows; and (5) pyrobitumen, which is mainly a non-generative solid bitumen, is evolved from thermal cracking of the remaining hydrocarbon residue and other types of solid bitumen in the dry gas window and higher temperature (Ro > 1.4%). This model shows concurrence of multi-populations solid bitumen with oil, bitumen, and other phases of fluid hydrocarbon residue during most of the maturity continuum.

Highlights

This paper presents a new schematic model for generation and timing of multiple phases of solid bitumen throughout the continuum of organic matter maturation in source and tight reservoir rocks
The evolution of organic matter immediately after sinking through the water column and deposition in sedimentary basins involves a series of post-burial bacterial activities and low temperature chemical reactions during the diagenesis stage, followed by thermal maturation and thermal cracking during the catagenesis and metagenesis phases
The low temperature reactions involving recently deposited organic matter lead to the formation of kerogen at the end of the diagenesis stage

Summary

Introduction

This paper presents a new schematic model for generation and timing of multiple phases of solid bitumen throughout the continuum of organic matter maturation in source and tight reservoir rocks. Bitumen and solid bitumen are secondary hydrocarbon products that are found in most source and tight reservoir rocks They are formed during different stages of the post-burial organic matter evolution continuum. This classification has ambiguously used “pre-oil solid bitumen” for both diagenetically formed solid bitumen in immature source rocks as well as the catagenetically generated solid bitumen at the beginning of the oil window (but just before onset of crude oil)[7,8] (Table 1) Both types of reported solid bitumens are formed before generation of liquid crude oil, there is, a drastic difference in the nature, genesis, and timing of these two types of “pre-oil” solid bitumens. This simple contradiction in the application of “pre-oil” between the two influential studies has caused a great deal of confusion and “pre-oil” bitumen/solid bitumen has been frequently used for two completely different p roducts[7,8,9,11]

Objectives

Findings

Conclusion