Anping Hu

Natural gas accumulation in eastern China

There are various genetic types of natural gas in eastern China, which are mainly of biogenic gas, abiogenic alkane gas and abiogenic CO2. Large biogenic gas fields discovered at present are mainly distributed in Ying-Qiong basin (Ya13- 1, Ledong22–1, Dongfang1–1), Pearl River Mouth basin (Panyu30–1), Eastern China Sea basin (Chunxiao gas field) and Taixi basin (Tiezhanshan gas field) in the continental shelf, and carbon isotope of ethane is heavier than −28‰, which shows that the gas is coal-derived. Large abiogenic alkane gas fields are distributed in the deep part of Songliao basin (Xingcheng gas field, etc), and the natural gas is characterized by heavy isotope (δ13C1>−30‰), negative carbon isotope series and R/Ra>0.5. CO2 gas fields distribute widely from Songliao basin in the north to Ying-Qiong basin in the south, and total 35 CO2 gas fields have been discovered in these areas with CO2 content more than 60% and d13Cco2 heavier than −28‰.

Origin of Marine Sour Natural Gas and Gas-Filling Model in the Puguang Giant Gas Field, Sichuan Basin, China

Taking the geology and tectonic evolution characteristics of the Sichuan Basin into account, the chemical and stable isotopic compositions of natural gas, and biomarker compounds in the reservoir bitumen in the Puguang giant gas field, are investigated to identify the genetic type of marine sour natural gas, take the gas-source correlation, and set up the gas-filling model of the Puguang giant gas field in the Sichuan Basin. The alkane gases in the field are dominated by methane, ranging from 22.06% to 99.64% with an average value of 76.52%, and the low content of heavy hydrocarbon gases are dominantly ethane and little propane. The H2S contents occur among the marine carbonate gas reservoirs, ranging from 0 to 62.17%, wherein the H2S contents in the Upper Permian Changxing Formation and Lower Triassic Feixianguan Formation range from 6.9% to 34.72% (average value=15.27%) and from 0% to 62.17% (average value= 13.4%), respectively, indicating that both are H2S-enriched reservoirs. The chemical and carbon isotopic compositions of marine natural gases show that the alkane gas in the Puguang giant gas field is dominantly oil-cracking gas at high maturity stage, and the biomarker characteristics of reservoir bitumen indicate that the major source rocks are the Upper Permian Longtan Formation sapropelic matters. Moreover, various levels of thermochemical sulfate reduction (TSR) were present in the process of oil-gas transformation, not only increasing the content of non-hydrocarbon gas components (CO2 and H2S) and decreasing the content of heavy hydrocarbon gases, but also causing the reversal of carbon isotope compositions of methane and ethane and the heavier carbon isotope of methane. The recovery of structural configurations over geological time investigates that the gas-filling history of Puguang giant gas field can be divided into three stages: formation of paleo-oil accumulation from the middle-late Indosinian period to the early Yanshanian period, thermal cracking of paleo-oil and TSR alteration from the early to the middle Yanshanian period, and adjustment of gas accumulation from the late Yanshanian to the early Himalayan period. The gypsum of the Lower Triassic Jianglingjiang Formation and the Middle Triassic Leikoupo Formation plays the most important role as effective seal to the gas preservation in different periods.

Determination of Total Alkalinity and Calcium Concentration of Seawater Rapidly and Automaticly with Small-Amount Samples

The means of determing total alkalinity(A t ) and calcium concentration of small-amount seawater samples using one set of equipments is described. Using automatic potentiometric titrator (Metrohm* 798MPT Titrino), through termostating, increasing the titration reagent volume accuracy, accurate positioning equivalence point and regulating reagent volume every step added, At and calcium can be measured separately with high precision and limited time. The relative standard deviation of At is lower than 0.10% (plusmn2 mumol kg -1 ) with a single sample consumption of 25cm3 and 9 min while the relative standard deviation of calcium is better than 0.25% (plusmn26 mumol kg -1 ) , sometimes lower than 0.10% (plusmn10 mumol kg -1 ) ,with a single sample consumption of 1.0 cm 3 and 5 min.