Effect Of Sand Volume On Production Pressure And Completion

Our country is rich in heavy oil resources in the tertiary unconsolidated sandstone reservoirs.Using the technology of CHOPS(cold heavy oil production with sand) to lead way of "moderate sand production",will increase oil production,and enhance economic benefits of oil industry. But because of the poor cementation and low intensity of rock mechanics of the layer system.During the process of CHOPS,lots of sand particles will get out of reservoir, so except the risks of pipeline blockage and erosion,people should pay attention to the wellbore stability induced by sanding. Therefore,designing a reasonable wellbore completion method and the drawdown pressure system corresponded with sand production have important realistic significance for the CHOPS.Based on a region of Bohai Sea which is rich in heavy oil in unconsolidated sandstones as the research object,and after research on the physical and mechanical characteristics of this type of sandstone, relationships between sand production rate,porosity and rock mechanics strength have been established.,besides there are the sanding criteria and constitutive equation On the basis,what have been done before achieved the aim of optimization of wellbore completion method.Besides binding with the actual wellbore parameters,a finite element mode has been established too.So on this platform,a series of differential critical drawdown pressure under different sand production rate have been calculated. In addition,combined with the results of finite element calculation,the research still considered the drag force which caused by fluid pressure,because it has certain effect on the critical drawdown pressure.Research shows that:(1) As to the unit volume core,the volumn of sand production rate equal to added value of porosity;in addition,because of the relationship of exponential decline between porosity and uniaxial compressive strength of unconsolidate sandstone,the UCS of the target position shows a same form during the process of sand flow;(2) For weakly cemented loose sandstone formation,even the sand amount is O,the instability of wellbore is inevitable,so peolpe must choose the casing well completion way. In addition,under the precondition of "moderate sand production",according to its own proppant carrying capacity,and actual situation,people can choose grave casing and sieve tubes;(3) Regard for the "reasonable sanding",equivalent plastic strain 6‰is chosed as the critical of wellbore failure and completion method, such as cementing the mainbore and junction or gravel pack and screen pipe completion。(4) Contrast sieve tube support completion and barefoot completion method, and compared with the sand between the regional volume changes from sand, it more easily with the completion of barefoot in the process of the regional stratigraphic wellborne cause more damage;(5) For the reservoir where we put attention,because of its special condition,even if the drawdown value is below 2MPa;sand particles will still move into the wellbore; Therefore,combined with the results of finite element calculation and fluid flow,we can see that the drage force has a certain effect on sand produciton rate and critical drawdown pressure;it makes critical down pressure lower than before.