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Exploration Potential Analyses Of The Shale Gas In Dongying Depression

Posted on:2012-03-27Degree:MasterType:Thesis
Country:ChinaCandidate:Z LiFull Text:PDF
GTID:2210330338967750Subject:Mineral prospecting and exploration
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The history of exploration and production in North America shows shale gas can generate and accumulate in the source rocks with a wide rage of thermal maturity, especially in high thermal maturity. The production of shale gas is strongly affected by the total organic carbon content, organic type, mineral composition, moisture content of pores and the distribution of inducible crack. in the shale. Fracturing and drilling are the key technology for shale gas exploitation.Bohai Gulf Basin is a Mesozoic-Neozoic terrestrial rift basin in the east of China. Dongying Depression lies in the southeast of Bohai Gulf Basin with the area of 5700km2. By the end of 2009, there are 110 exploratory wells have Oil &gas showings, 8 exploratory wells have industrial overflows in Dongying Depression.According to analysis of geochemical ,mineral, logging, drilling and seismogram data on palaeogene strata in Dongying Depression, t The shale of lower Es3 and upper Es4 in Palaeogene Lacustrine are the main source rocks in Dongying depression. The thickness of the dark mudstone of upper Es4 is about 250350m, the thickness of shale is mainly from 40 to120m, the buried depth is about 15764700m. The thickness of the dark mudstone of lower Es3 is commonly above 300m, with a maximum of 500m, the thickness of shale is 150200m, and the buried depth is about 1,500-4,200m.According to the analysis of geochemical, mineral, logging, drilling and seismogram data on palaeogene strata in Dongying Depression, the shale of lower Es3 and upper Es4 is characterized by large thickness, high abundance of organic matter, favorable types and wide range of maturity(Ro=0.35~1.5%). It has similar geological and geochemical characteristic comparing with North America and the material foundation generating shale gas.The abnormal high pressure occurs rather widely in the shale of lower Es3 and upper Es4 in Dongying depression. The maximum pressure coefficient in the center are more than 1.8 (except for Boxing sub-sag with pressure coefficient 1.5), the shale in Dongying depression has favorable pressure environment. The shale in this area has high content of quartz and carbonate and its clay content is less than 50%. It is similar to Haynesville shale and Eagle Ford shale. The physical property analysis of the shale shows that, the porosity is about 3%~12% and the permeability is 0.001~0.02mD. Comparing with the discovered shale gas reserves in North America, the shale in Dongying depression has favorable reservoir properties. The gas logging analysis on the shale of lower Es3 and upper Es4 shows abnormal phenomena. Moreover, well kick and leak frequently occurred during well servicing. These indicate the existence of gas. The light hydrocarbon abundance of head space gases increase with depth, while the∑(C5-C7)/∑(C1-C4) value is low, usually less than 0.15, which shows that the head space gases of the shale under 3400m are mainly gas. According to the relation of light hydrocarbon composition of head space gases and gas-to-oil ratio to buried depth, the exploration of the shale reservoir in Dongying Depression should be concurrent exploration, when the buried depth is less than 3400m, the exploration should give priority to oil reservoir, as for the buried depth is more than 3400 meters, the exploration should consider the condensate hydrocarbon reservoirs and gas reservoirs primarily. The gas reserves of shale of lower Es3 and upper Es4 in Dongying Depression was estimated with volumetric analysis. Comparing with the discovered shale gas reserves in North America, the gas reserves of Dongying Depression corresponds to that of Barnett and Haynesville shale and is more than others. So it has potential to form shale gas reservoir and it will be a new field of natural gas exploration.
Keywords/Search Tags:Dongying Depression, Palaeogene, shale gas, organic carbon content, mineral
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