TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAcoustic compressional slowness measurements are critical for geomechanics, petrophysical and seismic applications. Conventional acoustic wireline data is often unavailable due to cost constraints or well problems, thus increasing the need for acoustic Logging While Drilling (LWD). The LWD environment creates additional demands on borehole acoustic measurements as compared to wireline, due to tool strength requirements and drilling noise. These issues have consistently limited the LWD acoustic tool's ability to provide wireline equivalent data quality. The conventional LWD methods have incorporated single direction or single axis acoustic systems with short transmitter-receiver (TR) spacing (typically 4 ft). Technical features of a new acoustic LWD tool incorporating long TR spacing (+10 ft) with an array containing six fourelement receiver stations to obtain omni-directional measurements will be discussed. Field test data examples will show the improved quality of this real-time measurement.The tool configuration was optimized as a result of comprehensive modeling and lab testing of key system components. Greater source power combined with multifrequency adjustable signature capability allowed the TR spacing increase. The system quality was enhanced due to improved software and hardware functionality. An improved receiver array configuration allows for better noise isolation and response to formation arrivals. In addition, real-time downhole monitoring of the drilling noise coupled directly into the collar allows for further data quality enhancement. Redundancy and a modular design approach were key for providing a robust and reliable system with fast tool setup and data downloading.The field test examples will present data acquired in different drilling modes to demonstrate the improved signalto-noise ratio for raw and stacked data in both fast and slow formations. As compared to industry standards, faster Rate of Penetration (ROP) is achievable due to enhanced downhole processing capabilities. The real time slowness results compared to conventional wireline shows the systems' ability to make comparable measurements. These field test results demonstrate an improved data quality with this new LWD acoustic system.

Identification of drilling problems is most commonly achieved by simple comparisons of surface and downhole time-averaged measurements of weight and torque, or by shock and vibration sensors located either downhole or at the surface. Various drilling phenomena are more complex than can be described by these simple shock and vibration measurements. The interpretation of drilling vibration data collected at the surface requires specialized expertise, and can be difficult. Sometimes downhole phenomena are not interpretable at the surface. The diagnosis of bottom hole assembly (BHA) vibrations measured directly by a downhole tool is much easier. A prototype downhole assistant driller measurement-while-drilling (MWD) device has been constructed that unambiguously diagnoses drilling phenomena from sensors that are located in the BHA, and that are sampled at a high frequency. Processing algorithms programmed into the prototype identify bit bounce, stick-slip, backward rotation, torque shocks, BHA whirl, pressure anomalies and excessive stress. Drilling efficiency and specific energy at the bit are also calculated. Average weight and torque values as well as drilling diagnostics are transmitted to the surface and enable the driller to make real-time improvements to the drilling process in a timely manner. A key requirement for enhancing drilling performance is the ability to simply and clearly display information about the drilling process on the rig floor. The prototype display not only informs the driller about the severity of drilling phenomena, but also provides advice about how to eliminate particular drilling inefficiencies before they become problematic. The real-time drill floor display effectively completes the loop between the MWD prototype in the bottom hole assembly and the driller's controls. Additional displays and logs permit the post-drilling assessment of data from previously drilled intervals. The downhole assistant driller helps optimize the rate of penetration, and reduce bit, motor, MWD and other BHA component failures. Downhole drilling parameters, together with quality conventional surface measurements, identify drilling problems and help drillers better decide when to make short wiper runs, or when to trip for a bit. A method for closed-loop drilling operations is presented. This paper reviews the test program and draws conclusions from long term research with both downhole and surface drilling measurements. Actual field results demonstrate how downhole measurements provide a clearer feel for BHA behavior, and allow the driller to optimize the drilling process, reduce BHA component damage, and improve the efficiency of the drilling operation. Background Measurement-while-drilling technology has been used historically to help position a wellbore correctly, and to evaluate the geological formations around the wellbore In addition to having information in real time about where you are drilling, and what you are drilling. it can also be advantageous to have information about how the drilling process is proceeding. When using a hand drill one adjusts the applied force based upon vibrations, sound and reactive torque. Similarly, it is extremely useful to have real-time information from near the drill bit about the wellbore drilling process. The dynamics of bit, BHA and drillstring behavior have been studied both theoretically and experimentally for many years, and there are many publications in the literature. P. 743

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper presents the principle and engineering aspects of an LWD quadrupole shear wave tool. Extensive theoretical study and a series of laboratory and field experiments have been conducted to verify that the quadrupole measurements can determine the true shear velocity of the formation. Experimental results based on the actual laboratory and downhole while drilling measurements are presented in this paper. A multipole (i.e., monopole, dipole, and quadrupole) LWD acoustic tool has been constructed. This tool allows downhole recording of raw and stacked signals acquired by individual receiver elements of the tool. This tool consists of a universal source, which can operate at different frequencies in all three modes, i.e., monopole, dipole, and quadrupole. The six-station receiver array, with four individual receiver elements per station, permits signal acquisition in all these modes. In addition, a triaxial accelerometer system is used to monitor drilling dynamics while drilling.By making multiple snapshots of the signals in different modes downhole for various drilling conditions, we demonstrate that, when operating in the quadrupole mode, the acoustic signals acquired by the LWD tool possess the true quadrupole characteristics. Comparison of the dipole, monopole, and quadrupole signatures clearly demonstrates how common mode noise is efficiently suppressed in the quadrupole mode. The result shows that even in the case of severe lateral vibrations the combined quadrupole signal provides satisfactory shear wave measurements. The data processing/analysis results are presented. Field-measured quadrupole LWD shear data are evaluated for different drilling scenarios.

Real-time monitoring of BHA and drill bit dynamic behavior is a critical factor in improving drilling efficiency. It allows the driller to avoid detrimental drillstring vibrations and maintain optimum drilling conditions through periodic adjustments to various surface control parameters (such as hook load, RPM, flow rate and mud properties). However, selection of the correct control parameters is not a trivial task. A few iterations in parameter modification may be required before the desired effect is achieved and, even then, the result may not be optimal. For this reason, the development of efficient methods to predict the dynamic behavior of the BHA, and methods to select the appropriate control parameters, is important for drilling optimization. The approach presented in this paper uses the power of Neural Networks (NN) to model the dynamic behavior of the non-linear, multi- input/output drilling system. Such a model, along with an optimizing controller, provides the driller with a quantified recommendation on the appropriate corrective action(s) required to bring the system to an optimal drilling condition. Development of the NN model used drilling dynamics data from a field test. This field test involved various drilling scenarios in different lithologic units. The training and fine-tuning of the basic model utilized both surface and downhole dynamics data recorded in real-time while drilling. Measurement of the dynamic state of the BHA was achieved using data from downhole vibration sensors. This information, which represents the effects of modifying the surface control parameters, was recorded in the memory of the downhole tool. Representative portions of this test data set, along with the corresponding set of input-output control parameters, were used in developing and training the model. Test results are promising: There is good agreement between the dynamic behavior of the BHA predicted by the NN model and the actual measured BHA response. In addition, the test established criteria for selecting the most important input-output parameters and for selecting representative data sets for building and training the model. This analysis has demonstrated a promising approach to simulation and prediction of the dynamic behavior of the complex multi-parameter drilling system. This method could become a powerful alternative to traditional analytic or direct numerical modeling and its utilization could be extended beyond drilling dynamics to the field of drilling control and optimization.

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