Study On Single Well Controlled Reserves Of Multistage Fracturing Horizontal Wells In Carbonate Reservoirs

Carbonate reservoirs account for more than 50%oil and gas reserves in the world.However,most carbonate reservoirs are low-permeability reservoirs.At present,the horizontal wells or fracturing horizontal wells are mainly used for the production of these carbonate reservoirs with low permeability.The purpose is to increase the drainage area and the reserves of single wells,thereby promoting the efficient and rational development of low permeability carbonate reservoirs..The calculation methods of reserves mainly include static method and dynamic method.The static method generally uses volumetric method to calculate geological reserves.In dynamic methods,material balance method,water-flooding characteristic curve method,transient well testing method are used to calculate geological reserves or recoverable reserves,while Arps decline curve method can only be used to calculate recoverable reserves.In the view of the basic characteristics of carbonate reservoirs,the following research work have been carried out and the corresponding achievements have been achieved:First,the oil flow regularity from homogeneous reservoir to conventional multi-fractured horizontal well was studied.Based on this,the mathematical model of unstable seepage in the dual media fracturing horizontal wells was established.The analytical pressure and yield solutions of horizon well with artificial fractures were obtained by Laplace transform and Duhamel principle.The flow pattern of fluid and the corresponding sensitive parameter were analyzed and the dual media multi-fractured horizontal well unsteady seepage theory was obtained.Finally,the new theory was combined with material balance equation to form two methods to calculate single well controlled reserve,as listed.?The method of combining pressure buildup test and material balance equation?The method of combining material balance method and unsteady seepage modelFor carbonate reservoirs with high water cut,the multiphase flow around well hole will appear.However,the previous two approaches were not adaptable,the single well controlled reserve was acquired by fitting water cut using the relative permeability data.In summary,when using above methods to calculate single well controlled reserve of the target block,,there are great differences between calculation results because the principle of these methods are different.They have their own advantages and disadvantages on adaptability,simplicity and accuracy.Different methods apply to different stages,the choice of method depends on the stage of the reservoir.