Liu Wen-hui

Ternary geochemical-tracing system in natural gas accumulation

The establishment of geochemical-tracing system of gas generation and accumulation is helpful to re-elucidating the gas migration and accumulation in time and space. To deduce the complex process of gas accumulation, a ternary geochemical-tracing system is set up, according to stable isotope inheritance of source rocks, kinetic fractionation of stable isotopes, time-accumulating effect of noble gas isotopes, mantle-derived volatile inheritance, and organic molecule inheritance of light hydrocarbons and thermally kinetic fractionation in their generation, in combination with the previous achievements of gas geochemistry and geochemical parameters of gas-source correlation. There are tight interactions for the geochemical parameters with much information about parent inheritance and special biomarkers, in which they are confirmed each other, reciprocally associated and preferentially used for the requirement so that we can use these geochemical parameters to effectively demonstrate the sources of natural gas, sedimentary environments and thermal evolution of source rocks, migration and accumulation of natural gas, and rearrangement of natural gas reservoirs. It is necessary for the ternary geochemical-tracing system to predict the formation of high efficient gas reservoir and their distribution in time and space.

H2S formation and enrichment mechanisms in medium to large scale natural gas fields (reservoirs) in the Sichuan Basin

Abstract A comprehensive study on the temporal and spatial distribution of H 2 S accumulations and the geochemical characteristics of sour gas fields (reservoirs) in the Sichuan Basin has been conducted. It has been followed by a series of carefully designed simulation experiments to elucidate an H 2 S formation mechanism which is able to predict the distribution of H 2 S. In some reservoirs, for example P 2 ch(T 1 f, have sufficient magnesic SO 4 2( and abundant hydrocarbons (palaeo pools) present at sufficiently high temperatures to cause thermochemical sulfate reduction (TSR). This is the major origin of abundant H 2 S in large to medium scale gas fields. The formation mechanism of highly sour gas fields (reservoirs) is an in-situ reaction under conditions where sufficient source, enough energy supply, suitable reservoir volume and severely reducing environments occur. However, in some areas or strata, such as slope belts or on continental shelf deposits, or formations such as the Jialingjia and Leikoupo Formations, which are dominantly compact carbonatite and have contemporaneously different facies, it is difficult to form abundant H 2 S. These formations lack a source of sulphur and energy compared to the P 2 ch(T 1 f reef flat facies reservoirs. Even though highly sour natural gas migrating from the P 2 ch(T 1 f reservoirs is present, H 2 S is often consumed due to long distance migration and results in hydrocarbon-rich sweet natural gas. This study predicts that the Heichiliang reef flat facies sedimentary zone in northeastern Sichuan to have highly sour natural gas reservoirs.

CH4/N2 Ratio as a Potential Alternative Geochemical Tool for Prediction of Thermal Maturity of Natural Gas in Tarim Basin

Abstract In this context, the bulk ratio of CH 4 /N 2 is examined as a potential alternative geochemical parameter for the assessment of thermal maturity of natural gas and compared to other previously published data. Open-system non-isothermal pyrolysis of low-mature coal from the Manjiaer sag, Tarim basin, yielded generation curves for methane and nitrogen. Analysis of the change of vitrinite reflectance indicates a two-stage process of thermal maturation with increasing temperatures. The relationship between R o and pyrolysis temperature could be expressed by the following equations: Stage I: R o = 0.0014 T + 0.109, r = 0.9931( R o R o = 0.0067 T −1.5855, r = 0.9996 ( R o > 0.6%). A kinetic interpretation of the characteristics of nitrogen and methane generation in humic coal during laboratory pyrolysis indicates that the bulk ratios of methane and nitrogen as thermal maturity parameters may be applied to assess the maturity of gas-sources. Thus, the maturity of the source rocks of natural gases in the Tarim basin was expressed in terms of CH 4 /N 2 ratios and compared with other geochemical natural gas parameters, such as stable isotopes. The predicted results were found to be consistent with the published data.

Influences of water media on the hydrogen isotopic composition of natural gas/methane in the processes of gaseous hydrocarbon generation and evolution

The influences of water media on the hydrogen isotopic composition of organic-thermogenic natural gas were tested in three series of experiments on coal pyrolysis, with no water, deionized water (

An isotope study of the accumulation mechanisms of high-sulfur gas from the Sichuan Basin, southwestern China

\delta D_{H_2 O}

Comprehensive geochemical identification of highly evolved marine hydrocarbon source rocks: Organic matter, paleoenvironment and development of effective hydrocarbon source rocks

=−58‰), and seawater (

Geochemical characteristics of cherts of Lower Cambrian in the Tarim Basin and its implication for environment

\delta D_{H_2 O}

Bio-thermocatalytic transitional zone gases

=−4.8‰) added, respectively. The experimental results show that the productivities of H2 and CO2 obviously increased under hydrous conditions and that the productivity of CH4 also remarkably increased in the high-evolution phase of hydrous experiments. Water was involved in the chemical reaction of hydrocarbon generation, and then the hydrogen isotopic composition of methane was affected. There is a linear correlation between the hydrogen isotopic composition of methane and its productivity, as reflected in the three series of experiments. In the case of the same CH4 productivity, the hydrogen isotopic composition of the methane produced in anhydrous experiments was the heaviest, that of the methane produced in seawater-adding experiments came second, and that of the methane produced in deionized water-adding experiments was the lightest. The hydrogen isotopic composition of natural gas/methane is affected by the following factors: 1) the characteristics of hydrogen isotopic composition of organic matter in source rocks, 2) the thermal evolution extent of organic matter, and 3) fossil-water media in the natural gas-generation period. The experimental results show that the influence of the fossil-water medium in the natural gas-generation period was lower than that of the other factors.

CARBON ISOTOPIC REVERSED DISTRIBUTION OF THE SOLUBLE ORGANIC COMPONENTS FOR THE CAMBRIAN AND ORDOVICIAN CARBONATE ROCKS IN TABEI AND TAZHONG AREAS,TARIM BASIN

The mechanism of hydrogen sulfide (H2S) generation plays a key role in the exploration and development of marine high-sulfur natural gas, of which the major targets are the composition and isotope characteristics of sulfur-containing compounds. Hydrocarbon source rocks, reservoir rocks, natural gases and water-soluble gases from Sichuan Basin have been analyzed with an online method for the content of H2S and isotopic composition of different sulfur-containing compounds. The results of comparative analysis show that the sulfur-containing compounds in the source rocks are mainly formed by bacterial sulfate reduction (BSR), and the sulfur compounds in natural gas, water and reservoir are mainly formed by thermal sulfate reduction (TSR). Moreover, it has been shown that the isotopically reversion for methane and ethane in high sulfur content gas is caused by TSR. The sulfur isotopic composition of H2S in natural gas is inherited from the gypsum or brine of the same or adjacent layer, indicating that the generation and accumulation of H2S have the characteristics of either a self-generated source or a near-source.