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The Yanchang gas field is located in the Ordos Basin of central China to the southeast of the Yishan Slope, covers an exploration area of 2.6×10 km and has approximately 3.5×10 m of gas reserves. The gas field is dominated by lithologic gas reservoirs but also has a few structural gas reservoirs. Sand bodies were deposited in the Carboniferous Benxi Formation around offshore barrier islands and in distributary channel fillings in the delta front of the P s and P s divisions of the Permian Shanxi Formation. The P h division of the Shihezi Formation contains the main reservoirs. The depths of the reservoirs are between 1 970 and 3 500 m. The Yanchang gas field can be classified as a typical tight sandstone gas reservoir filed because its porosity is lower than 10% and permeability lower than 1 mD. The discovery and development of the Yanchang gas field has led to a great increase in total natural gas reserves in the Ordos Basin. Its exploration has improved methods of locating large gas fields in deep-water depositional environments in the south part of the basin. [ABSTRACT FROM AUTHOR]

The Western Depression of the Liaohe Basin is the major exploration area of the Liaohe Oilfield, and its main source rocks consist of the third and fourth members of the Shahejie Formation (Es and Es). These source rocks are widely distributed in the depression, with semi-deep lake and fan delta as the main sedimentary facies, brown oil shale and black gray-dark gray mudstone as the main rocks, and a total thickness of 270-1450 m. The kerogens are mainly of the types I and II, and partly of the type IIB and least of the type III. The R values range from 0.4%-0.8%, indicating an evolution stage from immature to mature. The maturity of Es source rocks is relatively high, reaching the early mature stage, but their distribution and thickness are lower than those of Es. Besides, according to biomarker analysis, it is thought that the source rocks of Es and Es are characterized by mixed input, and most of the source rocks were formed in the brackish water-saline and strongly oxygen-free environment. Furthermore, the Qingshui, Niuxintuo and Chenjia sags are believed to possess greater potential for hydrocarbon generation and expulsion, for they are source rocks with a larger thickness, have higher organic carbon contents, belong to better organic matter types and possess higher maturities. [ABSTRACT FROM AUTHOR]

One of the most important tasks of evaluating natural resources of petroliferous basins is to determine the organic matter abundance of source rocks in the basin. The usual method for assessing the organic carbon content of source rocks is based on laboratory analyses. There is a deviation in calculating organic carbon content due to the heterogeneous distribution of organic matter and the artificial factors when sampling. According to the continuous characteristics of information logging, the conventional logging curves (mainly acoustics and resistivity, etc.) were calibrated with the organic carbon experimental data of cores, cuttings or sidewall cores. The organic carbon content of source rocks of the 4 (Es) and 3 (Es) members of the Shahejie Formation in western sag in the Liaohe depression was estimated directly by a great amount of continuous data including resistivity and acoustic logging, etc. Comparison between the results from computer processing and lab analysis of logging data shows that the organic carbon contents derived from the computer processing of logging data have the same reliability and accuracy as the lab analysis results. The present data show that this method is suitable to evaluate the source rocks of western sag in the Liaohe depression and has great potential in evaluating natural resources of sedimentary basins in the future. On the basis of logging data of source rocks, experimental data and existing geochemical analyses of the Liaohe Oilfield, the corresponding total organic carbon (TOC) isograms of source rocks were plotted. The source rocks of Es and Es of the Shahejie Formation are thought to be beneficial to hydrocarbon accumulation due to the high TOC. [ABSTRACT FROM AUTHOR]