A New CFD Numerical Simulation Method for Mud-Positive Pulse Signal Generation and Propagation

Abstract

ABSTRACT Based on the theory of computational fluid dynamics (CFD), an integrated numerical model of the positive pulse generator with the upstream and downstream pipeline was established. Compared with the previous numerical simulation, this model can simulate the generation and transmission process of positive pulse signals efficiently and accurately for the first time. Based on the mechanical structure of the common positive pulse generator, the simplified two-dimensional axisymmetric geometric model of the flow region was established considering its flow symmetry characteristics. Combined with dynamic mesh and sliding mesh technology, the reciprocating motion of the valve is simulated, and a custom function controls the motion to generate low-frequency pulse signals. Comparing the new CFD model with the previous numerical model, it is found that with the periodic change of flow area, compression wave, and expansion wave are generated simultaneously in the upstream and downstream of the positive pulse, with the same frequency and opposite phase, which satisfies the transient hydrodynamics theory. Meanwhile, as the pressure wave propagates, the irregular pulse waveform becomes sinusoidal, and its amplitude decreases gradually. This paper presents a new CFD numerical model and simulation scheme, which can provide an efficient and accurate method for designing and simulating a mud pulse telemetry system. INTRODUCTION With the development of the global oil and gas exploration and development objects in the direction of "ultra-deep formation, unconventional formation, old development formation," the scale of horizontal wells has increased significantly, and there are many complex underground conditions (Antunes et al., 2015; Mwachaka et al., 2018). We need to integrate logging and measuring while drilling (LWD and MWD), downhole control, and big data analysis in real-time to solve the problems encountered during drilling and completion. As a wireless data transmission mode, mud pulse telemetry (MPT) has a long transmission distance, good economy, and wide application range (Jia et al., 2018; Chin et al., 2014). Among them, a positive pulse is developed earliest, with stable transmission and strong anti-interference ability.