Behzad Elahifar

Axial vibration monitoring in laboratory scale using CDC miniRig and vibration sensor sub

Since vibration and shock loads are always known as a destructive loads while drilling a borehole and reason for tool failure, more detailed studies of vibration and dynamic behavior of drill string and bottom hole assembly to prevent any time lost and hole problem is needed to be done. To achieve these objectives, monitoring the vibration in laboratory scale is performed. This paper describes a research in which drilling process and related vibration are monitored. A fully capable small drilling rig (CDC miniRig) and vibration sensor sub are used to measure them in different ranges of weight on bit and rotary speed of drill string. Dynamic stability window based on experimental test results to have minimum vibration is also suggested.

Wellbore Instability Monitoring by Using 4D Imaging of Ultrasonic Caliper Logs in Real Time Drilling

Drilling programs continue to push into new and more complicated environments. As a result, accurate measurement and analysis of drilling data in real time are becoming more critical by means of minimizing failure costs. The measurement of actual wellbore shape in real-time can be considered as one of the key components to detect problems such as borehole instability. Abnormal wellbore shape will allow drawing conclusions on the stress field. Accurate wellbore caliper measurements in real-time will also allow determining cement volume requirements with less measurement time. Measuring flow rate accurately behind the bit with ultrasonic sensor will also help the driller to detect washouts along drill string in real time. This paper describes experiments related to the accuracy of ultrasonic sensor measurements for estimation of wellbore diameter in drilling fluids with different mud weights and additives in real time. A fully automated test robot has been designed and tests have been performed in different drilling conditions. The test robot allows moving vertical as well as lateral movement of a sensor head in an artificial wellbore which can be run with different fluids. In addition, bubbles were added to the mud while measuring borehole diameter by the sensor. Tests have been performed in relation to the radial position of the caliper tool inside the wellbore, including different objects inside the borehole simulating latches or dog legs. The wellbore profiles have been measured with different axial and rotational surveying speeds. Numerical simulation of ultrasonic measurements and comparison of the results to the recorded data gives an estimate on the measurement accuracy at different RPMs of drill string. It is also shown that gas bubbles can be detected and compensated with an appropriate accuracy if circle fitting methods like the Kasa method in combination with robust error models are applied.

Accuracy of ultrasonic sensor in caliper log

An ultrasonic sensor has been developed for MWD (measurement while drilling) and LWD (logging while drilling) applications that perform real time borehole caliper measurements and also wellbore stability monitoring. The caliper determines the oval shape of the borehole with a defined accuracy and resolution. These measurements are transmitted to the surface and used to compensate MWD and LWD measurements. Furthermore, with early and accurate real-time caliper measurements, borehole instability can be detected. For example, an elliptical wellbore can indicate the maximum and minimum stress directions. Borehole enlargement or washout can indicate that the mud is too heavy or too reactive with the formation. An under-gauge borehole might indicate bit wear. Caliper measurements are also required to estimate the amount of cement to be used, which is an important environmental and safety concern. This paper describes experiments and specification of the ultrasonic sensor for measuring wellbore diameter. It explains the setup procedure and a rotating machine which is used to simulate the drill string on which the ultrasonic sensor is mounted. The accuracy and problems related to recording and processing of ultrasonic sensor data was investigated. Finally, measured and recorded data of ultrasonic sensor are compared to the simulated wellbore profile.