Research On Cementing Quality Evaluation Method Based On Acoustic Logging While Drilling

Cementing is an indispensable part of the petroleum industry,and it is related to the integrity and sustainability of oil and gas exploration,so cementing quality evaluation is very required.With the complicated exploration environment gradually increasing,such as deep water and deep formation drilling wells,the conventional wireline cementing quality inspection technology is costly and difficult and it takes up a lot of derrick time.For high-angle(large displacement)and horizontal borehole,wireline logging is difficult or impossible to measure because the well inclination is too large.The logging while drilling(LWD)technology can carry out multiple measurements when lowering or lifting the logging tool,which not only ensures the quality of the logging data but also saves the logging time and the economic cost.It is suitable for deep water and deep formation environment.The characteristics of the LWD tool can also make up the weakness that wireline logging crawler cannot go deep into measuring in high-angle and horizontal wells.At present,Schlumberger has mainly carried out research work on the LWD cement logging.However,its research mainly refers to the conventional wireline cementing quality evaluation method.They have not theoretically analyzed the LWD acoustic response characteristics of the cased well.Based on the propagation theory of elastic wave,we analyzed the LWD acoustic response characteristics of the cased well,and applied the simulation results to the processing and interpretation of actual data,which provides theoretical guidance for the LWD cementing quality evaluation.This thesis is mainly divided into the following three parts:In the first part,based on the propagation theory of elastic wave,a cased-borehole LWD acoustic wave model with columnar-layered elastic media is established.The LWD sound field expression of the cased well are derived.The dispersion characteristics of the casing wave and the collar wave are studied.The LWD full-waveforms under different cementation conditions are simulated using the real-axis integration method.Combining the slowness-time correlation method,the arrival time and amplitude characteristics of the casing wave,the collar wave and the formation wave are analyzed.The second part analyzes the influencing factors of LWD-casing acoustic wave array,including the variation of micro-ring thickness and acoustic parameters of cement-ring.It is found that the change of waveform with the degree of cementing quality can be better simulated by changing the shear modulus of cement-ring.Referring to the conventional cementing quality evaluation method,the casing wave amplitude(energy)and attenuation are calculated in a specific time window,and the law of amplitude and attenuation as a function of cementing quality is counted.The third part numerically simulates and compares the relationship between the amplitude and attenuation of the casing wave and the cement bond index of the LWD and wireline under different cementation degrees.It comes to forms a LWD acoustic cementing quality evaluation method that simultaneously utilizes the amplitude and attenuation of the casing wave,which realizes the division of various cement bond indexes under the LWD condition.The correctness of the theoretical calculation are verified by the example of the evaluation of cementing quality in the LWD field,and good application results are obtained.