库车坳陷吐北1井区古流体演化过程

Palaeofluid evolution process in Well Block Tubei 1 in the Kuqa Depression,Tarim Basin

塔里木盆地库车坳陷吐北地区受膏盐岩和断层的综合影响,其流体的历史演化过程复杂,但过去对此研究较少,制约了对该区油气分布规律的认识。为此,对吐北1井区的储集层进行了流体包裹体分析和定量颗粒荧光分析,并结合构造演化史、埋藏史、热演化史和生烃史恢复了该区的古流体演化过程。研究结果认为,该区经历了2期油气充注：1第一期为中新世—上新世康村组（N1-2k）早中期（距今16~9 Ma）原油充注,对应的包裹体荧光呈黄色、黄白色,各层段的定量颗粒荧光（QGF）指数均大于4,表明储层早期的确存在古油藏;而后期由于膏盐岩被断层切穿使得早期流体逸散,形成储层中的残余沥青,现今的储层表面吸附烃的三维全息扫描荧光光谱普遍显示单峰,也证明早期原油逸散。2第二期为上新世库车组（N2k）沉积晚期（距今3 Ma）天然气和轻质油充注,对应的包裹体为赋存于石英颗粒边缘的蓝色荧光包裹体以及黑色气态烃包裹体;该时期膏盐岩盖层埋深加大,强烈的塑性流动恢复了盖层的封盖能力,同时喜马拉雅造山运动使得圈闭剧烈隆升,聚集了大量的天然气和少量的轻质油。

Under the joint action of gypsum-salt rocks and faults, fluid evolution process is complicated in the northern Tuzimazha, Kuqa Depression, Tarim Basin. In the past, however, the oil and gas distribution rules in this area were less studied, so the related understanding was insufficient. In this paper, the reservoirs in Well Block Tubei 1 were analyzed by means of fluid inclusion and quantitative grain fluorescence （QGF） technologies. Based on tectonic evolution history, burial history, thermal history and hydrocarbon generation history, the palaeofluid evolution process in this area was reproduced. It is shown that the well block experienced hydrocarbon charge in two pe- riods. The first period is the early-middle stage （16-9 Ma） of Miocene Kangcun Fm （N1.2k）, when it was charged with oil, with the corre- sponding characteristics of yellow and white-yellow fluid inclusion fluorescence and the QGF Index higher than 4, indicating that there were palaeo oil reservoirs at the early stage of the reservoirs. And at the late stage, the fluids that were accumulated at the early stage escaped because the gypsum-salt rocks were cut by faults, and bitumen remained in the reservoirs. It is also the evidence for the escaping of the early charged oil that the three-dimensional spectral fluorescence （TSF） of the hydrocarbon adsorbed to the surface of the current reservoirs is generally unimodal. The second period is the late stage （about 3 Ma） of Pliocene Kuqa Fm （N2k）, when the natural gas and light oil charging occurred. Correspondingly, there are two inclusions, i.e. black gaseous hydrocarbon inclusion and blue fluorescence inclusion located along the edge of the quartz grains. At this stage, the gypsum-salt caprocks deepened and their sealing capacity was re- covered due to strong plastic flow. Moreover, the trap was uplifted violently under the effect of Himalaya orogeny, and a large amount of natural gas and a little heavy oil were accumulated.