Abstract
Accurate knowledge of circulating pressure and temperature is essential for making critical decisions while drilling operation. Through implementation of miniaturized semiconductor technology, we obtained near real-time dynamic pressure and temperature profile of the wellbore, making previously simulated critical operational data such as equivalent circulation density (ECD) and wellbore thermal distribution now measurable using drilling microchip. The application of drilling microchips to collect distributed pressure and temperature data while drilling is investigated, where each microchip measures both pressure and temperature simultaneously. This study also presents a revised method to calibrate measurements of drilling microchip with depth.
Four field trials were attempted in a slightly inclined well using water-based or oil-based muds, where 10 drilling microchips were deployed in each trial. The recovered data from the drilling microchips are first downloaded and compiled. An in-house software is developed to process and convert time-scale of each drilling microchip to depth considering slippage of drilling microchips in drill string and annulus. An iterative algorithm is designed to calibrate the predicted arrival time with the actual arrival time of each tracer, which ultimately yields the true velocity of tracers in flow conduits. The maximum measured pressure is used as an indicator to locate each tracer at the bottom hole. It is realized that a plateau of pressure versus time can signify a trapped tracer in the flow path if the pump rate was maintained constant.
The results of field trials show that some of the tracers were trapped for few minutes in the lower section of annular space or before the bit nozzle. The results of temperature profiles conclude a unique pattern for almost all of the deployed drilling microchips. However, the results of pressure profiles can be classified in two different groups as drilling microchips could have moved in different batches while pumping. The calculated temperature gradients show a heating zone near the bottom hole and continuous cooling of drilling fluid as tracers move toward the surface. The average pressure gradient is in the range of 0.52 – 0.61 psi/ft among different trials. It is shown that the velocity of tracers in each interval strongly depends on the flow regime.
To our best knowledge, a combined measurement of circulating temperature and pressure using drilling microchips for the first-time is successfully conducted in these field trials. The results can be used for calculation of ECD and temperature profiles, which provide near real-time downhole data for monitoring and diagnostic applications. The measured pressure data also provide new insights about tracking of drilling microchips in the wellbore.
