Determination Of Irreducible Water Saturation Of Tight Sandy Gravel In Xujiaweizi Fault Depression

Xujiaweizi fault depression is located in the middle part of Songliao Basin Xujiaweizi-Beian fault depression belt,west of the central paleo uplift,eastern connection Chaoyang ditch salient,in the north of the saddle and Lindian Heiyupao fault depression connected,the south is connected with wangfu fault depression.With the gradual depletion of conventional oil and gas resources,the difficulty o f exploration and development,the importance of unconventional oil and gas is becoming more and more important,and tight oil and gas is the most realistic exploration target in unconventional oil and gas resources.Many wells have encountered tight sandy gravel gas in Shahe Formation in Xujiaweizi fault depression,the irreducible water saturation is one of the most important parameters in the calculation of reserves,which is also the key parameter to distinguish the water and hydrocarbon zone,and to ca lculate the relative permeability and water production rate.Therefore,it is very important to determine the irreducible water saturation of tight sandstone in Xujiaweizi fault depression.In this paper,the tight sandy gravel of Shahe formation in Xujiaw eizi fault depression is studied by the basic theory of the theory of nuclear magnetic resonance,the theory of capillary and the theory of fluid mechanics.The author makes use of all kinds of experimental methods to determine the irreducible water saturation of tight sandy gravel in Shahe formation,and study on the variation of irreducible water saturation under normal temperature pressure and formation temperature pressure,finally,the lower limit of tight reservoir is determined by irreducible water saturation.Experimental results show: under normal temperature and pressure,the saturation of irreducible water measured by gas-water relative permeability is generally high,up to 90%,with an average of 79.8%,and the lower the permeability,the greater the irreducible water saturation;under normal temperature and pressure,the irreducible water saturation measured by nuclear magnetic resonance method is basically the same as that of the gas-water relative permeability method,followed by the constant speed mercury injection method,the worst of the high pressure mercury injection method;the irreducible water saturation at normal temperature and pressure is significantly higher than that under the condition of high temperature and high pressure,the difference between the two is about 32%,in the practical application,we should adjust the water saturation of nuclear magnetic resonance,the correction amount is about 30%,the average value of corrected bound water saturation is 55%;the pore volume of rock movable fluid is lower than that of bound water volume,irreducible water may exist in the reservoir space with large radius;the particle size of gritstone is crude,the sorting features is better,the compressive strength of the rock is stronger,and the throat radius is higher than that of conglomerate and fine sandstone,so gritstone has lower irreducible water saturation;the shale content of pore type rock is less,the throat radius is larger,the pore is more developed,and the connectivity between pore and throat is the best,so pore type rock has lower irreducible water saturation;the lower limit of tight reservoir throat radius in Xujiaweizi is about 27 nm.Based on the analysis of the irreducible water saturation of the Shahe formation,which to lay a solid foundation for further evaluation the potential of Xujiaweizi reservoir,determination oil and gas enrichment area and optimization well loction.It also provides an important theoretical basis for realizing the breakt hrough of oil and gas exploration and improving the oil recovery in the study area.