scholarly journals Characterization of the reservoir-caprock of the large basement reservoir in the Dongping field, Qaidam Basin, China

2018 ◽  
Vol 36 (6) ◽  
pp. 1498-1518 ◽  
Author(s):  
Feng Ma ◽  
Wei Yang ◽  
Yongshu Zhang ◽  
Hongzhe Li ◽  
Mei Xie ◽  
...  
Keyword(s):  
Qaidam Basin ◽  
Solution Space ◽  
Source Rocks ◽  
Dominant Factor ◽  
Basement Rock ◽  
Gas Reservoirs ◽  
Large Reservoir ◽  
Heterogeneous Distribution ◽  
Gas Accumulation ◽  
The World

The basement gas reservoir in the Dongping field in the Qaidam Basin is a large reservoir that is different from other basement reservoirs around the world. The basement reservoir does not contain thick mudstone with abundant organic matter that acts as both a source rock and a caprock. The natural gas came from lateral Jurassic source rocks. The basement lithologies in wellblocks Dp3, Dp1, and Dp17 are granite, granitic gneiss, and limestone with slate, respectively, but they all provide effective reservoir space for gas accumulation. The average porosities are 3.3%, 5.2%, and 3.6%, respectively, and the average permeabilities are 0.66 mD, 0.60 mD, and 0.57 mD, respectively. Tectonic fractures are the main factor for improving the physical properties of the reservoir, and secondary solution space is the key factor for the high and stable gas production in the study area. The E1 + 2 Formation, which contains abundant anhydrite, unconformably overlies the basement rock. Some of the anhydrite was deposited as cement and filled the fractures and pores, which led to decreased porosity and to the formation of a tight caprock with a high breaking pressure for hydrocarbon accumulation. The caprock becomes thinner from the lowland to the uplift, and it is missing in wellblock Dp3, which led to the heterogeneous distribution of gas. Anhydrite-bearing caprock is the dominant factor that controls the gas accumulation in the basement rock reservoir in the Dongping field. Studying the spatial distribution of the anhydrite-bearing caprock is important to the exploration and development of basement gas reservoirs in the Qaidam Basin. This unique gas accumulation mechanism in a basement rock reservoir may inspire new ideas for exploring basement oil and gas reservoirs around the world.

Genesis of hydrogen sulfide in natural gas reservoirs in Western Qaidam Basin

2020 ◽  
pp. 1-31
Author(s):  
Tian Jixian ◽  
Jian Li ◽  
Hua Kong ◽  
Xu Zeng ◽  
Xiaobo Wang ◽  
...  
Keyword(s):  
Hydrogen Sulfide ◽  
Natural Gas ◽  
Qaidam Basin ◽  
Source Rocks ◽  
Mature Stage ◽  
Lake Basin ◽  
Large Area ◽  
Gas Reservoirs ◽  
Western Qaidam Basin ◽  
Natural Gas Reservoirs

In recent years, gas reservoirs containing high levels of hydrogen sulfide have been found in salinized lacustrine carbonate rocks in the upper member of the Lower Ganchaigou Formation (E32) in the Yingxiongling area of the western Qaidam Basin. This poses great safety risks to drilling and development. To clarify the genetic mechanisms of hydrogen sulfide, we analyzed thegeochemical characteristics and sulfur isotopes of natural gas, and predicted the distribution of hydrogen sulfide. The results show that: (1) Natural gas in the Yingxiongling area is dominated by wet gas, with relatively high non-hydrocarbon content. The gas is E32 oil-type gas in a mature stage. (2) Hydrogen sulfide in natural gas reservoirs is less likely to originate from biological and volcanic geneses, and is primarily a product of thermochemical sulfate reduction (TSR). The high-quality Oligocene source rocks distributed across a large area, the saline-deposit formations widely distributed in the western Qaidam Basin, and the high geothermal gradients and large numbers of developed pore-type reservoirs, all combine to provide favorable conditions for the formation of hydrogen sulfide reservoirs. (3) During the E32 deposition period, rock salt developed in the center of the lake basin, the sealing conditions for oil and gas were favorable, and the formation temperature was high during the reservoir formation period. Development of sub-salt porous reservoirs is conducive to enrichment of hydrogen sulfide, and comprehensive prediction indicates that the sub-salt formation in the Central Yingxiongling-Gancaigou area is an enrichment zone for hydrogen sulfide. The research results are of considerable significance for the exploration and deployment, and the production safety, of hydrogen sulfide-containing reservoirs.

scholarly journals Fluid geochemistry of the Jurassic Ahe Formation and implications for reservoir formation in the Dibei area, Tarim Basin, northwest China

2018 ◽  
Vol 36 (4) ◽  
pp. 801-819 ◽  
Author(s):  
Shuangfeng Zhao ◽  
Wen Chen ◽  
Zhenhong Wang ◽  
Ting Li ◽  
Hongxing Wei ◽  
...  
Keyword(s):  
Natural Gas ◽  
Tarim Basin ◽  
Oil And Gas ◽  
Northwest China ◽  
Source Rocks ◽  
Coal Measure ◽  
Hydrocarbon Generation ◽  
Gas Reservoirs ◽  
Isotopic Analyses ◽  
Jurassic Coal

The condensate gas reservoirs of the Jurassic Ahe Formation in the Dibei area of the Tarim Basin, northwest China are typical tight sandstone gas reservoirs and contain abundant resources. However, the hydrocarbon sources and reservoir accumulation mechanism remain debated. Here the distribution and geochemistry of fluids in the Ahe gas reservoirs are used to investigate the formation of the hydrocarbon reservoirs, including the history of hydrocarbon generation, trap development, and reservoir evolution. Carbon isotopic analyses show that the oil and natural gas of the Ahe Formation originated from different sources. The natural gas was derived from Jurassic coal measure source rocks, whereas the oil has mixed sources of Lower Triassic lacustrine source rocks and minor amounts of coal-derived oil from Jurassic coal measure source rocks. The geochemistry of light hydrocarbon components and n-alkanes shows that the early accumulated oil was later altered by infilling gas due to gas washing. Consequently, n-alkanes in the oil are scarce, whereas naphthenic and aromatic hydrocarbons with the same carbon numbers are relatively abundant. The fluids in the Ahe Formation gas reservoirs have an unusual distribution, where oil is distributed above gas and water is locally produced from the middle of some gas reservoirs. The geochemical characteristics of the fluids show that this anomalous distribution was closely related to the dynamic accumulation of oil and gas. The period of reservoir densification occurred between the two stages of oil and gas accumulation, which led to the early accumulated oil and part of the residual formation water being trapped in the tight reservoir. After later gas filling into the reservoir, the fluids could not undergo gravity differentiation, which accounts for the anomalous distribution of fluids in the Ahe Formation.

GEOLOGICAL REASONING FOR THE PETROLEUM SOURCE ROCKS OF KNOWN FIELDS

1986 ◽  
Vol 26 (1) ◽  
pp. 132
Author(s):  
R.E. Chapman
Keyword(s):  
Crude Oil ◽  
Source Rocks ◽  
Petroleum Geology ◽  
Single Source ◽  
Reservoir Rocks ◽  
Water Composition ◽  
The World ◽  
Distinct Source ◽  
Wax Content ◽  
Giant Fields

Geological reasoning for the petroleum source-migration-accumulation relationships centres around petroleum composition and its variability, water composition and its variability, and stratigraphy. For example, a field with several pools of petroleum of different compositions is likely to have been sourced from several distinct source rocks that are stratigraphically associated with the reservoir rocks. If water compositions are also variable, the conclusion is reinforced. A field with several pools of petroleum of similar quality was sourced either from similar source rocks that are stratigraphically associated with the reservoirs, or from a single source that is removed from the accumulations. There are also considerations of wax content, environment of deposition of the reservoir sequence, sand/shale ratios, and faulting.Geological reasoning does not always lead to the same conclusions as geochemical reasoning. Such cases are particularly important for petroleum geology because they should lead us to a better understanding of the source-migration-accumulation relationships. Some of the remaining giant oil accumulations of the world may be in areas that would be discarded on geochemical evidence. Most of the crude oil remaining to be discovered will be in relatively few giant fields, so misunderstanding could jeopardize our future supplies.

scholarly journals Distribution Characteristics and Influencing Factors of Uranium Isotopes in Saline Lake Waters in the Northeast of Qaidam Basin

Minerals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 74
Author(s):  
Chen Zhao ◽  
Pu Zhang ◽  
Xiangzhong Li ◽  
Youfeng Ning ◽  
Liangcheng Tan ◽  
...  
Keyword(s):  
Influencing Factors ◽  
Saline Lakes ◽  
Natural Waters ◽  
Qaidam Basin ◽  
Influencing Factor ◽  
Dominant Factor ◽  
Uranium Isotopes ◽  
Distribution Characteristics ◽  
Total Dissolved Solid ◽  
Lake Waters

Four saline lakes in the northeast of Qaidam Basin were selected to explore the distribution characteristics and influencing factors of uranium isotopes in lake waters with high evaporation background. The 238U concentration and the activity ratios of 234U/238U ([234U/238U]AR) showed that there was no significant change in the same lake, but there was a certain degree of difference in the distribution between different lakes. We found that aqueous 238U concentration within a certain range increased with an increase in TDS (total dissolved solid) and salinity, as was also the case with pH. As in natural waters, the pH affects the speciation of 238U, but TDS and salinity affect the adsorption process of aqueous 238U. Further, the replenishment of water will also affect the uranium isotope concentration for lakes, but it is not the main influencing factor for saline lakes. Therefore, we suggest that pH is the dominant factor affecting changes in aqueous 238U concentration of the sampled saline lakes. The [234U/238U]AR in these saline lakes are closely related to the input water and the associated water–rock interactions involving sediments, atmosphere dust, and organic material, etc. during the evolution stage, metamorphous degree, and hydrochemistry of the saline lakes. Lake water samples collected in the maximum and minimum discharge water period, were used to evaluate the seasonal distribution characteristics of aqueous 238U, and we found that 238U concentration did not show an evident change with the seasons in these saline lakes. If the 238U concentration and [234U/238U]AR can remain consistent during a period of time, then the sediment ages and/or sedimentation rates could be determined by lake sediment and/or biogenic carbonate in future, thus allowing for the accurate reconstruction of the paleoclimate and paleoenvironment.

scholarly journals Evaluation of oil and gas potential of blocks A and B Song Hong basin and suggested exploration plan

2015 ◽  
Vol 18 (4) ◽  
pp. 12-31
Author(s):  
Luan Thi Bui
Keyword(s):  
Oil Recovery ◽  
Oil And Gas ◽  
Petroleum System ◽  
Basement Rock ◽  
3D Seismic ◽  
Oil Accumulation ◽  
Recovery Coefficient ◽  
Gas Accumulation ◽  
Risk Parameters ◽  
Gas Potential

Basing on the structure, stratigraphic, depositional conditions and petroleum system the petroleum prospect, Song Hong northern basin, particularly, blocks A and B was evaluated. SIgnificantly high gas potential areas are Hong Ha, Sapa and Bach Long Bac structural sections. Predominantly oil potential is found in Hau Giang and Vam Co Dong structural areas. Low gas potential is found in Cay Quat and Ben Hai structural sections and low oil potential is found in Vam Co Tay, Chi Linh, Do Son and Tien Lang structural areas. The result of the calculation of a petroleum accumulattion capacity at the local, enhanced recoveral volume, risk parameters for stored gas and oil amount in blocks A and B are the oil potential in Kainozoi basement rock (KZ): oil accumulation volume at the local is 1722.9 million barrels (273.9 million cubic meters); oil recovery coefficient is 0.25 %; oil recoverable amount is 430.7 million barrels (68.5 million cubic meters). The gas potential in Miocene structural areas: gas accumulation volume at the local is 1620 BSCF (45.8 billion cubic meters); gas recoverable amount is 972 BSCF (27.5 billion cubic meters). The coefficient of success is quite low at 0.18 - 0.31 for gas and 0.08 – 0.23 for oil. Suggestion for the exploitation and exploration in further steps is to servey the 3D seismic in a 1500 square kilometer area and drill 2 wells for the exploration.

scholarly journals Organic and Inorganic Carbon Isotope in Cenozoic Source Rocks of the Qaidam Basin (China)

2020 ◽  
Author(s):  
Shixin Zhou ◽  
Ji Li ◽  
Kefei Cheng ◽  
Cheng Zhang ◽  
Zexiang Sun ◽  
...  
Keyword(s):  
Carbon Isotope ◽  
Inorganic Carbon ◽  
Qaidam Basin ◽  
Source Rocks ◽  
Organic And Inorganic Carbon
Sign in / Sign up

Export Citation Format

Share Document