Study On Numerical Simulation And Cementing Evaluation Method In Fluid Filled Double Casing Well

Cementing plays a pivotal role in the development of oil and gas wells,and evaluating cementing quality is significant to oil and gas field exploration and development With the continuous development of oil exploration technology,the completion measures of double casing or multi-layer casing are adopted in deep and ultra-deep wells.In addition,with the passage of some old oilfield injection-production development time and the implementation of a series of stimulation measures which increase oil production,the whole original well section will be added one more casing or above the damaged well section a smaller casing is put down hole by hanger to cement wells again.Therefore,double casing wells are more and more common,and the cementing quality evaluation of double casing wells is becoming increasingly important.Compared with single-layer casing wells,the number of radial layers and interface in double-layer casing wells are apparently more.Currently,the widely used well cementing quality logging evaluation technology,due to the limited detection depth,is difficult to detect the cementing condition between the outer casing and the formation.This study is based on COMSOL finite element software and simulates the response characteristics of monopole array acoustic logging in different cementing conditions of double casing wells,which lays a theoretical foundation for the application of array acoustic logging in the evaluation of cementing quality of double casing wells.By comparing the amplitude and velocity characteristics of casing wave under different cementing conditions in each interface.the results show that the amplitude of casing wave is the largest under the condition of free casing.When all interfaces are well bonded,there is basically no casing wave,and formation wave can be observed.With the increasing distance from I,II,III and IV unbonded cementing interface to the well axis in double casing wells,the change of casing wave amplitude is not linear However,the casing wave velocity decreases obviously with increase of the distance between the unbonded cementing interface and the well axis,so the casing wave velocity change can be used to evaluate the cementing condition of each interface in the evaluation of cementing quality of double casing wells.The phenomenon of time delay of casing wave is also observed in CBL / VDL result map of double casing well in oil field.In addition,compared with the single-layer free casing well in inner casing location,due to the existence of outer casing,the amplitude of casing wave will increase in the double-layer free casing well section,so it is necessary to select the amplitude of single-layer free casing section to do calibration when using the relative amplitude of casing wave to evaluate the cementing quality.In the simulation of full wave waveform,the main component contain Stoneley wave besides casing wave.This paper further discusses the feasibility of evaluating cementing condition between the outer casing and the formation by using the external Stoneley wave which is excited when the fluid is completely filled between the two casing layers.The numerical simulation results show that the slowness of the external Stoneley wave in the fluid ring increases significantly when the outer casing and the formation cementing condition changes from bad bonded to well bonded.This phenomena mentioned above can be used to judge the return height of the cement ring between the outer casing and the formation when fluid filling between the two casing layers.Due to the lack of array acoustic data of double casing wells,it is failed to verify the feasibility of using the frequency dispersion of the external Stoneley wave to judge whether the outer casing is cemented.