Research On Strength Timeliness Of Anhydrite Rocks Immersed In Distilled Water And Crude Oil

With the rapid development of national economy,there is a growing demand for oil in China,the petroleum reserve in our country is only about 40 days,but the international standard is up to 90 days.Using large oil storage tank to reserve oil on the earth's surface is the most common way in our country,compared with the this way,using underground oil depot is more environmental,safety and can save more land resource,reduce more cost.To cope with the serious situation of insufficient oil reserves,our government has planed three phase of the construction of national strategic oil reserve base.Except for the granite,gypsum as a storage medium,the deep gypsum mine also formed a space of underground mining goaf which has considerable size,large buried depth,good stable performance,high seal degree.It will provide another way for underground oil and gas reserves if optimized the utilization of resources.This paper focus on the stability of surrounding rock influenced by the physical and mechanical properties of and a series of laboratory tests were carried out.The differences of anhydrite's physical and mechanical properties between before and after water/oil immersed were analyzed and weakening mechanism of surrounding rock under oil storage environment was revealed.The work and achievements in this paper are as follows:(1)The mechanics parameters of natural anhydrite rock like shear wave velocity,compressional wave velocity,dynamic poisson's ratio,dynamic elastic modulus,expansibility,expansion pressure were obtained through wave velocity test and expansion test.Anisotropic property and expansibility of natural anhydrite rock were obtained.(2)The mechanics parameters of natural anhydrite rock like compressive elastic modulus,tensile elastic modulus,compressive poisson's ratio,tensile poisson's ratio,cohesive force and friction angle were obtained through Triaxial test,Uniaxial test and Brazilian split test which is also a contrast study compared to that in water or oil immersed conditions.(3)Anhydrite specimens were put into high-pressure environment in water or in oil around respectively during about 69 d,136 d,271 d for each time period.On the on hand,the uniaxial compression test,triaxial compression test and the Brazilian splitting test were carried out on every immerse conditions and corresponding mechanical parameters were obtained.One the other hand,the test showed that either water or oil has no much influence on the mechanical properties of anhydrite,and there is a sound feasibility to take anhydrite mining area as the storage for crude oil.Meanwhile,Water-Rock interaction and Oil-Rock interaction has the fairly weakening effect on the integral anhydrite rock,which indicated that by applying water cushion to reduce product loss and to ensure the quality of product can be promoted.