Implications for Ediacaran biological evolution from the ca. 602 Ma Lantian biota in China

The morphologically differentiated benthic macrofossils of algae and putative animal affinities of the Lantian biota in China represents the oldest known Ediacaran macroscopic eukaryotic assemblage. Although the biota provides remarkable insights into the early evolution of complex macroeukaryotes in the Ediacaran, the uncertainty in its age has hampered any robust biological evaluation. We resolve this issue by applying a petrographic-guided rhenium-osmium (Re-Os) organic-bearing sedimentary unit study on the Lantian biota. This work confines a minimum age for the first appearance of the Lantian biota to 602 ± 7 Ma (2σ, including decay constant uncertainty). This new Re-Os date confirms that the Lantian biota is of early–mid Ediacaran age and temporally distinct from the typical Ediacaran macrobiotas. Our results indicate that the differentiation and radiation of macroscopic eukaryotes, and the evolution of the primitive, erect epibenthic ecosystem, occurred in the early–mid Ediacaran and were associated with highly fluctuating oceanic redox conditions. The radiogenic initial 187Os/188Os ratios derived from the Lantian (1.14 ± 0.02) and other Ediacaran shales invoke oxidative weathering of upper continental crust in the early–middle Ediacaran, which may have stimulated the evolution of life and oceanic-atmospheric oxygenation. Integrated with published Ediacaran chronological and geochemical data, our new Re-Os geochemical study of the Lantian black shale provides a refined, time-calibrated record of environment and eukaryote evolution during the Ediacaran

Field control technologies of combustion assisted gravity drainage (CAGD)

Abstract: The targets, strategies and approaches of the field controlling processes of combustion assisted gravity drainage (CAGD) are discussed based on the research of its mechanisms, advantages and defects. By taking fully advantage of gravity, CAGD process can produce the mobilized oil near the combustion front through the underlying horizontal well, serving as a possible solution for extra-heavy oil production in Xinjiang oil field. However, unidirectional conning and breakthrough of combustion front are risky to happen during the field application of CAGD. Based on laboratory three-dimensional physical simulation experiments and the experience of former pilots, it is proposed that a gently upward sloping combustion front is beneficial for the steady drainage of mobilized oil and should be the target of CAGD control. Key production parameters like the maximum production rate and corresponding air injection rate during field application are calculated with reservoir engineering approach and material balance theory. The maximum oil production rate of the CAGD pilot in Block Fengcheng, Xinjiang oil field, is 12.9 m3/d, and the air injection rate is 14 048 m3/d. To maximize the oil productivity and sustain combustion front moving forward steadily, the ignition position should be located at the mid-upper parts of the formation; the air injection rate at the early stage should keep slow and increase gradually; meanwhile, the production rate of flue gas should be 90% of the air injection rate. A pilot of CAGD was initiated in the Xinjiang Fengcheng Field on the basis of those research outcomes. By the end of 2016, Well Group FH005 in the pilot has succeeded in steady production for more than 400 days. Key aspects, involving the shape of combustion chamber, oil production of single horizontal producer, air oil ratio and the degree of oil upgrading are in accordance with what the development plan predicted. Key words: super-heavy oil reservoir, fire flooding, combustion assisted gravity drainage, physical simulation, pilo

Evolution Characteristics of Overburden Strata Structure for Ultra-Thick Coal Seam Multi-Layer Mining in Xinjiang East Junggar Basin

The efficient and safe extraction of ultra-thick coal seam in the Xinjiang East Junggar Basin has been a major focus in the future of mining in China. This paper systematically studied the overburden strata fracturing process and the structure evolution characteristics based on a typical ultra-thick coal seam condition in Xinjiang, using both physical and numerical modeling studies. The interactions between shields and the roof strata were also examined, from the perspective of ground support. The results indicated that roof structure was mainly in the form of voussoir beam at the early mining stage, where overburden stability was affected by the rock mass properties and mining parameters. The support load mainly included top coal and immediate roof gravity load and the load caused by main roof rotary consolidation. As a result of mining disturbance and strata movement, the overlying strata re-fractured in the later mining stage. The roof structure changed from beam to arch gradually and propagates upwards with the increase of multi-layer mining times. The support load was mainly the gravity load of the friable rock mass within compression arch. The results will provide a guideline for the improvement of roof stability under similar mining conditions in Xinjiang