Shale Oil and Gas Generation Process and Pore Fracture System Evolution Mechanisms of the Continental Gulong Shale, Songliao Basin, China

Abstract

Continental shale oil is a new source of oil, and its formation and evolution mechanism is one of the most important scientific problems in its effective exploration and development. In this work, the hydrocarbon generation mechanism, occurrence of oil and gas, and pore structure characteristics were studied through a series of pyrolysis experiments using an improved closed experimental system, combined with chloroform extraction, two-dimensional nuclear magnetic resonance, and computed tomography, for the continental Gulong Shales, Songliao Basin. The results show that hydrocarbon generation from organic matter of continental Gulong shale follows a sequential reaction model, with adsorbed oil as an “intermediate” at Ro of 0.9–1.1%. The free oil reaches the generation peak and begins to convert to natural gas, and the gas/oil ratio increases rapidly when Ro > 1.3%. These suggest that the favorable oil generation window for Gulong shale is that Ro is between 0.9 and 1.6%. With oil generation, the shale pore structure and permeability change with maturity accordingly. The corresponding Ro for rapid porosity and pore volume increase is 0.9–1.2%, while Ro is greater than 1.2% for rapid permeability change as a result of the large amount of adsorbed oil converting into free oil. It is found that hydrocarbon generation and pore-forming materials are mostly lamalginite and the organic-clay complex, and their volumes shrank while generating hydrocarbon, forming pores and fractures along the layers and “sponge-like” pores, respectively. When Ro > 1.2%, the shale oil generation peak, pore development peak, and overpressure evolution peak are coupled, providing favorable conditions for shale oil and gas enrichment in continental Gulong shale. These experimental findings mutually prove and confirm the practice of Gulong shale oil exploration, and it may have important theoretical and practical significance for continental shale oil exploration and discovery in other basins.

Petroleum Retention, Intraformational Migration and Segmented Accumulation within the Organic‐rich Shale in the Cretaceous Qingshankou Formation of the Gulong Sag, Songliao Basin, Northeast China

“…Therefore, the TOC correction factor of the investigated succession was found to be 1.54. This value is basically consistent with previous experimental results (approximately 1.6) (Sun et al, 2022). The Rock-Eval pyrolysis of 25 sealed and pressure-preserved coring samples from well B was carried out on-site to obtain S 1t , which included gaseous hydrocarbons and retained oils thermally extracted/cracked before 300°C.…”

Research on Performance Evaluation of Polymeric Surfactant Cleaning Gel-Breaking Fluid (GBF) and Its Enhanced Oil Recovery (EOR) Effect

“…Continental shale is mainly formed in semi-deep-water to deep-water lacustrine sedimentary environments. The distribution area of the shale series is small, with diverse lithofacies types and poor structural environment stability [8,9]. Meanwhile, continental shale reservoirs are highly heterogeneous, with well-developed micro-and nano-pores and low development of organic pores, which leads to a complex distribution and small area of the "sweet areas" [10,11].…”

Storage Capacity and Microdistribution of Pore Water in Gas-Producing Shales: A Collaborative Evaluation by Centrifugation and Nuclear Magnetic Resonance

“…Connate water universally occurs in oil/gas shales in multiple forms of structural, crystal, adsorbed, and free water. − Structural and crystal water exist in the shale matrix skeleton (e.g., clay minerals), while adsorbed and free water are stored in various pores developed within the shale matrix, which are known as pore water. It has been generally accepted that the water primarily adsorbs on the hydrophilic pore spaces provided by clay minerals carrying negative charge and organic matter with oxygen functional groups, , which have high affinity for water, and secondarily adsorbs on the hydrophobic surface through weak binding energies; the free water is potentially distributed in the middle of pores adjacent to the adsorbed water.…”