Estimation Of Dynamic Reserves Of Fractured-Cavity Carbonate Reservoirs In Tahe Oilfield By Well Test Method

The proven reserves of fractured–cavity carbonate reservoirs in Tahe oilfield was abundant.However,with the exploration and development of the past 20 years,it is shown that there are great differences of the fractures and caves reservoirs underground in Tahe.And the combinatorial structures of fractures and caves were various.Besides,the serious heterogeneity of the reservoir,leading to the contradictions between previous development methods and the actual production has become increasingly prominent.Such problems as the dropping of formation energy,the rising of water cut,and the seriously declining of production.So it was hard to estimate the dynamic reserves of single well,well unit or all reservoirs so far,which has brought great difficulties for the late development of the adjustment measures and making development programs.Therefore,this paper proposed three new well test interpretation models for different combination of fractures and caves in Tahe.Which was based on a large number of literature research at home and abroad relevant and comprehensive geological,logging,drilling,completion,dynamic data and test data,etc.They were well-fracture-cave single permeability model,well-fracture-double caves parallel model,and well-cave-fracture-cave series model respectively.Furthermore,the mathematical differential equations of each model are given which based on the parameters such as the volume of underground cave,the length of fractures and the pipe flow pattern for cave.Then these three models are solved in Laplace space,and used Stehfest numerical inversion method to obtain the numerical solution of each model in real space.And then use the Matlab software programming the cave volume,fracture length and other parameters of the double logarithmic typical curve drawing and sensitivity analysis.In the type curve,only one concave can be found in the well-fracture-cave single permeability model and two concaves appeared in the well-fracture-double caves parallel model,which indicates that each cave begins to respond to the fracture supply.In the well-cave-fracture-cave series model,the pressure curve and the pressure derivative curve form a closed loop.The length of the fracture mainly affects the time of the concave appeared in the pressure derivative curve.The longer the fracture,the later the concave is,and the longer the time the pressure wave is transmitted to the wellbore.The slower the response of the cave to the fracture.And the cave volume mainly affects the depth and width of the concave in the pressure derivative curve.The larger the volume of the cave,the greater the depth of the concave,the greater the elastic energy of the internal fluid,the stronger the liquid supply capacity.In addition,the dynamic reserve calculation formula of three new models is given by using the well test method.And the well test method is applied to the AD26,AD11CH and TH12409 wells.According to the dynamic type curve fitting,we can obtain the cave volume,fracture length or other parameters.The dynamic reserves of the three wells are about 5.02×10~4 tons.2.67×10~4 tons and 7.38×10~4 tons respectively.