| Since Dushanzi oil was discovered in1937, Sikeshu Sag has experienced75years of exploration history, aniticlinal trap high focus that buried less than4200m all have been drilling, then Kayindike oil and Xihu oil and gas construction were found. After years of exploration, it has a good understanding of the research of Sikeshu sag’s hydrocarbon accumulation, and accumulated a certain amount of data.As an important exploration area of the southern margin of Junggar basin, geologists have done some evaluation work of oil and gas. The book The third evaluation of oil and gas resource in Junggar basin in2000and Petroleum system’s formation, evolution and evaluation of Sikeshu sag, Junggar basin’s southern margin by Wang Lihong in2002have all made calculation about the oil and gas resouse of Sikeshu sag. However, previous exploration studies’degree is not deep, the study of working area’s endogenous reservoir-cap is not meticulous and accurate enough, research techniques and means aren’t as mature as today, the calculation results can’t scientifically guiding nowadays exploration decision.Oil and gas resource evaluation is a dynamic process, so conclusions of one stage may not apply to all stages. As Sikeshu sag’s exploration has reached to some extent, in order to improve the efficiency of oil and gas exploration in the next job, we need to define the total volume of oil and gas resource of Sikeshu depression on the basis of previous research, and determine the favorable exploration and target area. Thus, determine and adjust the investment and exploration direction scientifically.Choosing what kind of method to calculate the resource is very important. It has significantly affection on the establishing of suitable model of working area, estimating and evaluating quantity of underground oil and gas resource. Oil and gas resource’s calculation including three aspects:hydrocarbon generation quantity、hydrocarbon expulsion quantity and resource’s calculation, it is the quantification of oil and gas resource’s evaluation.The study is on the basis of sorting, digesting and absorbing predecessors’ research achievements, making full use of the existing seismic, drilling, logging and various testing data, utilizing various techniques and methods to analyze source-reservoir-cap condition systematically, combining with a certain degree of technical means to evaluating working area’s oil and gas resource. The main working steps are as following:1.On the basis of previous studies, we evaluate geochemical characteristics of source rock in the working area. The average value of organic carbon in Paleogene Anjihaihe formation is0.93%, of chloroform bitumen "A" is0.04%, of total hydrocarbon quantity is180.43ppm, of rock pyrolysis hydrocarbon generation is3.74mg/g, evaluation of organic material abundance is good, types of organic material kerogen is Ⅱ1-Ⅱ2, average value of Ro is0.68%, source rock thermal evolution is in low mature-early mature stage. The hydrocarbon generation condition of Low Jurassic Sangonghe formation is good, average value of organic carbon is2.46%, of chloroform bitumen "A" is0.0649%, of total hydrocarbon quantity is418.73ppm, of rock pyrolysis hydrocarbon generation is11.45mg/g, evaluation of organic material abundance is moderate-good, types of organic material kerogen is Ⅱ2, average value of Ro is0.82%, source rock thermal evolution is in mature stage. Badaowan formation and Xishanyao formation source rock’s evaluation is bad, have little contribution to hydrocarbon’s supply. Combining logging data, sedimentary evolution and geochemical characteristics of hydrocarbon source rock, Middle-Low Jurassic source rock hydrocarbon’s generation center mainly distribute in the south to Aika fault zone, among the area, Gaoyuan-Wusu district that exist in the middle of sag and northeast Dushanzi district are the best. The hydrocarbon’s generation center of Anjihaihe source rock is in the south Kayindike、east Gaoquan and central and southeastern of sag.2.According to the data of lithology and sedimentary facies, combining with indicators such as reservoir property and pore structure, we can evaluate reservoir types in the working area, and then determine reservoir’s distribution characteristics. Tertiary of Sikeshu sag mainly develops class Ⅱ、Ⅲ reservoir, class I and class V are few. Class Ⅱand Ⅲ mainly distribute in Kaindike and Dushanzi district, class Ⅲand IVdistribute in Xihu district.3.This paper mainly researches middle-upper cap rock of Sikeshu Sag. On the top of Taxihe formation, west of working area, develops gypsum mudstone30m～120m thick, with strong capability of sealing gland. On the north side, bottom of Taxihe formation develops abnormal high pressure, with strong capability of sealing gland. Anjihaihe formation develops Lake Facies mudstone that become thinner from southeast to southwest, with abnormal high pressure and strong capability of sealing gland.4.According to the combination of hydrocarbon source bed, reservoir, cap rock in space, on the basis of previous studies, this study will divide the combination into4sets of source-reservoir-cap assemblage:①lower source and upper reservoir source-reservoir-cap assemblage:Paleogene Anjihaihe formation(source)Neogene Shawan formation(reservoir) Neogene Taxihe formation(cap);②continuance、 self-generation and self-bearing source-reservoir-cap assemblage:Paleogene Anjihaihe formation dark color mudstone (source) Paleogene Anjihaihe formation shore-shallow lake sandstone (reservoir) Paleogene Anjihaihe formation excess pressure mudstone (cap);③discontinuity、 lower source and upper reservoir source-reservoir-cap assemblage:Middle-Lower Jurassic dark color mudstone and coal petrography (source) Jurassic Qigu formation (reservoir) unconformity and calcarinate mudstone in the bottom of Cretaceous (cap);④complex、lower source and upper reservoir source-reservoir-cap assemblage:Middle-Lower Jurassic dark color mudstone and coal (source) Paleogene Ziniquanzi formation (reservoir) Paleogene Anjihaihe formation excess pressure mudstone (cap).5.Oil and gas resource calculation includes three aspects:hydrocarbon generating quantity、hydrocarbon expulsion quantity and resource calculation. In the research we use data to calculate the hydrocarbon of source rock; the data gets from the kerogen pyrolysis simulation experiment. According to the law of conservation of matter, hydrocarbon generation quantity minus hydrocarbon remaining quantity can get hydrocarbon expulsion quantity. In the working area, total resource quantity is4.6636×108, total hydrocarbon generating quantity of Anjihehai formation is0.6810×108t.Total hydrocarbon generating quantity of Middle-Lower Jurassic is3.9826×108t, thus Middle-Lower Jurassic oil and gas system is the mainly system of Sikeshu Sag.6.The study combines the development and distribution of the hydrocarbon source, reservoir development, trap development, oil and gas migration passage systems, capping conditions, preservation condition and the spatio-temporal relationship between these factors, divided Sikeshu sag into three kinds of exploration potential district: Ⅰ-Ⅲ. Among them, Xihu anticline and Dushanzi anticline are favorable structural trap. Following is Ka-6Well east block and Gaoquan east anticline. Due to restriction of various reservoir forming conditions, other anticline traps’ effectiveness is poor.Considering actual geological conditions of working area in the study, we establish the resource calculation model. While selecting the suitable geologic parameter, but because of the restriction of working area exploration degree, some data is not enough, if only arithmetic the parameters simply, the results cannot show actual situation of working area, also cannot provide scientific advice to the next exploration decision, thus,using Monte Carlo method to deal with the parameters, and stimulate simple data through imitation as much as possible, close to the situation of underground, finally getting the expectation reserves value curve, it is corresponded to different probability value, with more persuasive. |
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