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Research On Tight Sandstone Reservoir Characteristics Of The Third Member Of Shahejie Formation In Shuangtaizi Structural Belt And Its Surrounding Areas

Posted on:2015-01-14Degree:MasterType:Thesis
Country:ChinaCandidate:H FangFull Text:PDF
GTID:2180330431472643Subject:Mineral prospecting and exploration
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Having gone through more than40years’exploration and development, Liaohe Depression has been in highly-mature exploration stage and the exploration targets has been changed from traditional conventional hydrocarbon reservoirs into unconventional ones. Taking the western sag as an example, its exploration degree is up to71%. Tight sandstone gas reservoirs have become the important field to improve the reserves and steady the deliverability. Shangtaizi structural belt is located in the central south section of the western sag, closely adjacent to the largest hydrocarbon-producing sag of Liaohe Depression, that is, Qingshui sink, possessing sufficient hydrocarbon source. Shangtaizi structural belt and its surrounding areas in Liaohe have large residual resources, and the shallow clastic reservoirs have been essentially verified. Thus, the middle and deep reservoirs have become the further exploration priority. The strata below3000m in the research area basically belong to tight reservoirs. The prospecting of tight hydrocarbon has been an important field. Paleogene third member of Shahejie Formation is buried deep and has adequate gas source with high thermal evolution, high organic abundance, in favor of producing large quantity of natural gas. During the period when the third member was formed, Shangtaizi structural belt sediments were provided by the central and western bulge provenance system. Sublacustrine fan sand bodies are developed widely and the reservoirs are low-porosity, low-permeability and tight, which contact directly with the hydrocarbon source rocks, laying good reservoir and hydrocarbon foundation for the forming of tight sandstone gas accumulations.The research target of this paper is the third Member tight sandstone reservoirs in Shangtaizi structural belt and its surrounding areas of the western sag. Aimed at the sedimentary evolution, reservoir characteristics, effective reservoir distribution rules of tight sandstones, with the application of multidisciplinary theories and methods such as sequence stratigraphy, sedimentology, reservoir geology and geophysics, tight reservoir characteristics of the third member in Shangtaizi structural belt and its surrounding areas have been analyzed at first. Then full use of important exploration well analysis and test results and previous achievements has been made, and the development conditions for favorable reservoirs have been analyzed from the structural, sedimentary and diagenetic aspects, the relation between pore texture and physical properties and other aspects. At last the main influence factors of reservoir properties have been determined and the distribution features of payable reservoirs have been predicted, providing references for the exploration of the tight sandstone hydrocarbon accumulations in Shangtaizi structural belt and its surrounding areas.The third member of Shahejie Formation in the research area is a second-order sequence, which has been subdivided into three third-order sequences, corresponding to the lower, middle and upper part of the third member. Sublacusttine fan-semi deep and deep lacustrine deposition is predominant in the research area, which is dominated by coarse-grained gravity flow deposit. Influenced by the western and central bulge provenance systems, the middle sub-member of the third member is the most widespread and thickest in sublacustrine fan deposit. Sublacstrine fan sand bodies are the most developed at braided channel microfacies in the middle fan sub-facies, whose reservoir properties are in the range of tight sandstones, offering good reservoir conditions to form tight sandstone gas pools.Lithic arkose and feldspathic litharenite predominate in the tight reservoirs of the third member, dominated by line and point-line contact, pore-type cementation and grain support with low composition and texture maturity; compaction, pressolution, cementation, metasomasis and denudation are common, among which compaction and cementation are the main factor in damaging porosity and decreasing permeability of reservoirs, while denudation produces secondary corroded pores and improves properties of reservoirs.Owing to the large buried depth and strong diagenesis, reservoirs of the third member are generally tight. Interparticle and intraparticle pores, pores inside of the interstitial materials and seam-like pores predominate, which are all secondary; five basic pore combinations have been concluded. The secondary pores are caused by the altered feldspar and detritus by organic acids, which are produced by karogen thermal degradation while the poor sorting and high shale content is bad for their development. Through multiwell analysis, there are thought to be three secondary pore belts vertically in the third memberof Shuangtaizi structural belt, that is, the depth ranges of2600m to3100m,3800m to4100m and4450m to4700m.Through comprehensive research on reservoir attributes, sedimentation and diagenesis are thought to be of significant influence on reservoir properties. It has been concluded that the lacustrine fan braided channel sand bodies have the best properties, followed by the middle fan front facies and interchannels, and the outer fan subfacies has the worst properties. What’s more, porosity and permeability of the reservoirs become poor with the depth increasing. Compaction damages the reservoir properties while denudation improves. Combined research results of reservoir characteristics, analysis and test data, sedimentary facies and diagenetic facies with pilot production data, the Shansan member reservoirs have been classified into4types according to porosity and permeability. On the basis of individual well assessment, comprehensive reservoir quality evaluation in the research area has been done, and it has turned out type Ⅲ reservoirs are dominated by sublacustrine middle fan front subfacies, and the tight reservoirs gradually decrease from the lower part to the upper part of the third member. The lower and the middle parts of the third member have widespread tight reservoirs, which are the main exploration horizons for tight hydrocarbon. Deprived from the oil test data of Shuangshen3well, Shuang216well, Shuang232well and Shuang213well and comprehensive analysis, the next exploration strategy is to further explore the tight hydrocarbon of the upper Shangsan submember of Shuangtaizi structural belt and to keep on the deep tight sandstone hydrocarbon prospecting of the southern Shuangtaizi structural belt.
Keywords/Search Tags:third member of Shahejie Formation, tight sandstones, sublacustrine fandeposit, reservoir characteristics
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