Paleoporosity and critical porosity in the accumulation period and their impacts on hydrocarbon accumulation—A case study of the middle Es3 member of the Paleogene formation in the Niuzhuang Sag, Dongying Depression, Southeastern Bohai Bay Basin, East China

Petroleum Science, Oct 2014

Similar reservoir sandbodies and fault conduit systems in the sandstone reservoirs in the middle Es3 member of the Niuzhuang Sag have been problematic for a long time. The following problems remain unsolved: 1) The distribution of sandstone porosity is inconsistent with the hydrocarbon accumulation. The oil sandstones have low porosity instead of high porosity. 2) Sandstones, which have the same properties, have different levels of oiliness, and the sandstones with almost the same properties show different degrees of oil-bearing capacity. This study analyzes the condition of reservoirs in the research area during the accumulation period in terms of paleoporosity estimation and discusses the critical porosity of the sandstone reservoirs during the same period. The following conclusions can be drawn from the results. 1) Although reservoir properties are low at present and some reservoirs have become tight, the paleoporosity ranging from 18% to 25% is greater than the critical porosity of 13.9%. As the loss of porosity is different in terms of burial history, the present porosity cannot reflect porosity during the accumulation period. Similarly, high porosity during the accumulation period does not indicate that the present porosity is high. 2) The present reservoir location is consistent with the distribution of high paleoporosity during the accumulation period. This result indicates that high porosity belts are prone to hydrocarbon accumulation because of the dominant migration pathways generated as a result of property discrepancies under similar fault conduit conditions. Consequently, the hydrocarbon mainly accumulates in high porosity belts. Paleoporosity during the accumulation period is found to be a vital controlling factor. Therefore, high paleoporosity sandstones in the middle Es3 member of the Niuzhuang Sag have great potential for future exploration.

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Paleoporosity and critical porosity in the accumulation period and their impacts on hydrocarbon accumulation—A case study of the middle Es3 member of the Paleogene formation in the Niuzhuang Sag, Dongying Depression, Southeastern Bohai Bay Basin, East China

Pet.Sci. Paleoporosity and critical porosity in the accumulation period and their impacts on hydrocarbon accumulation-A case study of the middle Es member of the Paleogene formation 3 in the Niuzhuang Sag, Dongying Depression, Southeastern Bohai Bay Basin, East China Liu Mingjie 2 3 Liu Zhen 1 2 Sun Xiaoming 1 2 Wang Biao 0 2 0 member , Niuzhuang Sag, Bohai Bay Basin 1 State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing) , Beijing 102249 , China 2 China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2014 3 School of Geoscience and Technology, Southwest Petroleum University , Chengdu, Sichuan 610500 , China Similar reservoir sandbodies and fault conduit systems in the sandstone reservoirs in the middle Es3 member of the Niuzhuang Sag have been problematic for a long time. The following problems remain unsolved: 1) The distribution of sandstone porosity is inconsistent with the hydrocarbon accumulation. The oil sandstones have low porosity instead of high porosity. 2) Sandstones, which have the same properties, have different levels of oiliness, and the sandstones with almost the same properties show different degrees of oil-bearing capacity. This study analyzes the condition of reservoirs in the research area during the accumulation period in terms of paleoporosity estimation and discusses the critical porosity of the sandstone reservoirs during the same period. The following conclusions can be drawn from the results. 1) Although reservoir properties are low at present and some reservoirs have during the accumulation period. Similarly, high porosity during the accumulation period does not indicate that the present porosity is high. 2) The present reservoir location is consistent with the distribution of high paleoporosity during the accumulation period. This result indicates that high porosity belts are prone to hydrocarbon accumulation because of the dominant migration pathways generated as a result of property discrepancies under similar fault conduit conditions. Consequently, the hydrocarbon mainly accumulates in high porosity belts. Paleoporosity during the accumulation period is found to be a vital controlling factor. Therefore, high paleoporosity sandstones in the middle Es3 member of the Niuzhuang Sag have great potential for future exploration. Paleoporosity; critical porosity; dominant migration pathways; hydrocarbon accumulation - Hydrocarbon mainly migrates during the accumulation period. Both primary and secondary migration is closely related to the properties of reservoirs. The capacity of the hydrocarbon to migrate to sandstone reservoirs depends on the pressure difference between the source rocks and the reservoir rocks and indicates the lower limit of sandstone reservoirs in the accumulation period. The indicated lower limit is a critical property of sandstone (Liu et al, 2006; 2007a; 2012) . Hydrocarbon can accumulate only if reservoir porosity is greater than the critical porosity. S e v e r a l s t u d i e s f o c u s o n t h e l o w e r l i m i t o f t h e petroliferous reservoir, and many methods have been proposed to determine the cutoff value (Guo, 2004; Wang et al, 2009; Cao et al, 2009) . In addition, quantitative analyses have been performed on the lower porosity limit (Pang et al, 2003; Zhu et al, 2006; Zhu, 2008; Jiao et al, 2009) . Although much research has been done on the cutoff value of sandstone, these studies focus only on the accumulative condition of the reservoir at present. The critical porosity of the reservoir during the accumulation period is seldom studied. By researching the main controlling factors of lithologic reservoirs in different types of basins, Liu et al (2006; 2007a; 2012) proposed the theory of four-factors mainly controlling accumulation, wherein the critical porosity during the accumulation period was determined to be one of the factors. Pan et al (2011a) determined that the critical porosity of tight sandstone in the Chang 8 member in the area, the critical porosity of the Chang 8 member sandstone 2012). Several problems have remained unsolved for a long time in the middle Es3 member of the Niuzhuang Sag. The oiliness of sandstones in the same reservoir is different, thus indicating that the sandstones with low properties possess superior oil-bearing capacity; the oil-bearing sandstones with similar properties have different degrees of oil-bearing capacity. Conventional accumulation theories have been unable to provide satisfactory solutions to these problems, as the present properties will not be the same as the properties during the accumulation period. In this study, we attempt to examine this by analyzing the relation between reservoir porosity and hydrocarbon formation and enrichment. 2 Geologic setting and stratigraphy The Bohai Bay Basin, an important hydrocarbonproducing basin in China, is located in eastern China and covers an area of approximately 200,00 (...truncated)


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Mingjie Liu, Zhen Liu, Xiaoming Sun, Biao Wang. Paleoporosity and critical porosity in the accumulation period and their impacts on hydrocarbon accumulation—A case study of the middle Es3 member of the Paleogene formation in the Niuzhuang Sag, Dongying Depression, Southeastern Bohai Bay Basin, East China, Petroleum Science, 2014, pp. 495-507, Volume 11, Issue 4, DOI: 10.1007/s12182-014-0365-y