Qun Luo

Progress and development trend of unconventional oil and gas geological research

Abstract The progress in pore structure characterization, hydrocarbon occurrence state, mechanism of oil and gas accumulation, main controlling factors and high production model of unconventional oil and gas is reviewed. The unconventional oil and gas geological research developed from observation of the nanopores to quantitative full scale and 3D pore structure characterization, from macroscopic occurrence state study to microscopic occurrence state evolution discussion, from differential pressure drive and preferential channel migration to staged accumulation and wettability preferential migration, from accumulation controlled by source to accumulation jointly controlled by source-reservoir assemblage and preservation conditions, from accumulation model to enrichment and high production model, revealing the research progresses and future trends of unconventional oil and gas geology. Challenges are presented in unconventional oil and gas geological theory, enrichment conditions and recoverable resources potential of deeply buried unconventional oil and gas, combination of unconventional oil and gas geological research and engineering technique, and basic geologic research for joint mining of different unconventional oil and gas resources.

Characteristics and formation mechanisms of tight oil: A case study of the Huahai Depression, Jiuquan Basin, Northwest China

The exploration of tight oil reservoirs has achieved a big success, especially in the Huahai Depression, Jiuquan Basin, China, but the characteristics and formation mechanisms of the tight oil reservoir are unclear. In this paper, a series of analyses including thin section, scanning electron microscope, gas chromatography–mass spectrometry, isotope, and fluid inclusions were taken to study the tight reservoirs of the Xiagou Formation (K1g) and Zhonggou Formation (K1z) in the Huahai Depression. The results show that the main factors influencing the porosity and permeability of the tight reservoir are the compaction and two periods of carbonate cementation. The second type of carbonate cementation was related to the decarboxylation of organic acids in parts of the study area. The tight oil accumulation periods for different formations are confirmed, during 115–102 Ma in K1g1, 114–97 Ma in K1g2, and 103–85 Ma in K1z1, respectively. The tight oil migrations are executed for only several meters vertically but hundreds of meters even kilometers laterally. Two kinds of formation mechanisms exist in the study area. The main formation pattern is the “hydrocarbon accumulated after reservoir had tightened,” which has occurred in most of the study area. The other pattern, the “hydrocarbon accumulated during reservoir was tightening,” is found in several places of the study area.