库车坳陷膏盐岩对异常高压保存的控制作用

近年来 ,库车坳陷所发现的大中型天然气田 (藏 )几乎都具有异常高压的特征 ,且在纵向剖面上异常高压位于古近系库姆格列木组和新近系吉迪克组膏盐岩之下 .这说明了库车坳陷天然气的富集成藏与异常高压密不可分 ,而异常压力又与膏盐岩有十分重要的关系 .因此 ,研究膏盐岩与异常高压之间的关系对于认识高压气藏的成藏有重要意义 .通过对库车坳陷地质概况、膏盐的分布特征及地层压力特征的研究 ,探讨了膏盐岩对异常高压的控制作用 .结果表明 :在平面上 ,库车坳陷膏盐的分布从盆地边缘向盆地中心逐渐加厚 ,具有西部厚、东部薄的特点 .而异常高压的分布呈南北分带的反“S”型 ,高压区分布在中带 ,表现为受膏盐岩分布的控制 .膏盐岩不但具有强烈的塑性 ,而且本身具有很高的突破压力和超压 ,对异常高压起到了压力和物性的双重封闭 ,有效地阻止了异常高压的泄露 ,进而使得高压气藏得以完好保存

Controlling effect of gypsum and salt rocks on abnormally high pressure in Kuche Depression

The medium—large gas reservoirs discovered in Kuche Depression in recent years are almost characterized by abnormally high pressure, and the abnormally high pressure is vertically under the gypsum and salt rocks of Paleogene Kumugeliemu Formation and Neogene Jidike Formation. This shows that the formation of the gas reservoirs in Kuche Depression has close something to do with abnormally high pressure, and the abnormally high pressure has something to do with gypsum and salt rocks. So the study on the relationship between gypsum and salt rocks and abnormally high pressure is important to the recognition of the formation of high pressure gas reservoirs. The controlling effect of gypsum and salt rocks on abnormally high pressure is discussed through studying the geological situation, the distribution of the gypsum and salt rocks and the characteristic of the formation pressure in Kuche Depression. It is shown that the gypsum and salt rocks are gradually thickened from the boundary to the center of Kuche Depression, and the thickness of the gypsum and salt rocks is greater in the west than in the east. The distribution of abnormally high pressure is characterized by conversed “S” zonation in N—E direction, which is controlled by the distribution of the gypsum and salt rocks. The highest pressure lies in the middle zone. The gypsum and salt rocks with great plasticity is characterized by high breakthrough pressure and overpressure, so they seal the high pressure by two mechanisms of pressure and physical property. Thus the gypsum and salt rocks effectively prevent the abnormally high pressure from leaking and protect the integrality of the high-pressure gas reservoirs.