INTRODUCTION OF A NEW OMNI-DIRECTIONAL ACOUSTIC SYSTEM FOR IMPROVED REAL-TIME LWD SONIC LOGGING - TOOL DESIGN AND FIELD TEST RESULTS

摘要

Demand for real-time acoustic measurements has been increasing with recent deliveries from Logging While Drilling (LWD) formation evaluation sensors on drill collars. The ability to provide quality real-time acoustic slowness allows the operating company to address a number of key cost-saving drilling issues. Real-time depth/time tie of the bit to surface seismic, acoustic porosity and inputs for geological and rock mechanics analyses are the most notable. The solutions, using these inputs, provide quicker decisions for efficient wellbore placement and time savings during the drilling process. The challenge facing acoustic development teams today is in providing continuous compressional and refracted shear slownesses in varying geological environments under the constraints presented by the drilling process. Systems need to be developed that reduce the effects of drilling noise, tool modes, and borehole-guided waves that are far worse than their wireline counterparts. This is accomplished by incorporating optimum source and receiver architecture for improved detection of formation signals. A compliment to the hardware is proper implementation of surface and down-hole software algorithms to enhance the detection of formation arrivals over borehole and tool mode contamination. A new LWD acquisition system will be introduced. Unique design features, such as omni-directional source and receiver arrays, illustrate how signal to noise can be enhanced. Comparisons of data from stacked single-array versus stacked summed-array measurements will be presented. Adaptive filtering techniques are also applied for reduction of drilling-related interference, such as bit bounce, mud flow, BHA whirl and stick slip. In addition, the performance of the transmitter to receiver isolation system will be presented. An investigation of the impact of the above mentioned design enhancements for quality LWD acoustic logging will be made through analysis of field test results. Data has been acquired in wells with varying slowness values in both hard and soft rock environments.