Factors affecting the attenuation of mud positive pulse signals in measurement while drilling and optimization strategies

Abstract

During measurement while drilling (MWD), mud pulse signals experience significant attenuation as they propagate upward due to the properties of drilling fluid and frictional losses. This makes decoding surface signals challenging, while the downward propagation of signals to the wellbore can lead to formation blowout. Therefore, it is essential to analyze the factors influencing mud positive pulse attenuation and develop an optimization method to enhance surface signal reception while mitigating bottom-hole pressure fluctuations This paper establishes a mud positive pulse transmission attenuation model based on one-dimensional water hammer theory, solved using the method of characteristic lines. Wavelet decomposition and reconstruction are applied to extract positive pulse amplitudes from the simulation results. The study employs control variates to investigate the effects of drilling fluid density, consistency coefficient, liquidity index, mud pump rate, and well depth on mud pulse signal attenuation. These factors are further used as decision variables in the Non-dominated Sorting Genetic Algorithm II (NSGA-II) to propose a dual-objective optimization method tailored for ultra-deep wells with narrow safe density windows. The results demonstrate strong agreement between the model predictions and measured bottom-hole pressure in terms of amplitude and inflection point timing, validating the model’s accuracy. Within certain ranges, increasing drilling fluid density leads to greater attenuation of the positive pulse amplitude transmitted to the surface. The attenuation rate shows a pattern of initial increase, followed by a decrease, and then another increase. Additionally, increases in the consistency coefficient, liquidity index, mud pump rate, or well depth result in higher attenuation of the positive pulse amplitude, with a corresponding rise in attenuation rate. In a 7000-m vertical well, the proposed optimization method reduces the bottom-hole negative pulse amplitude by approximately 90.7% to 92.6% and enhances the positive pulse amplitude at the riser by 33.3% to 50.7%. This study provides significant theoretical and methodological guidance for the application of MWD systems in drilling operations