Untethered Pressure Sensor Conveyance for Bottomhole Pressure Measurement

Abstract

Abstract Bottomhole pressures of wells are commonly used to evaluate reservoir characteristics such as permittivity and permeability and connectivity between wells. To measure bottomhole pressure, a sensor needs to be conveyed either through an invasive method such as wireline, or it can be permanently installed downhole. These methods can be costly. In this paper, we are introducing a new conveyance method using an untethered well logging tool. We used an untethered well logging tool that can autonomously move in the vertical parts of liquid wells by changing its buoyancy. It takes a small dissolvable weight to descend in a well, and at a programmed depth the weight is released to make the tool buoyant. The recorded data can be retrieved after the tool returns to the surface. We expanded this tool’s capability so that it can land at the bottom of the well and stay for a programmed time frame. To do this, the dissolvable weight was coated to delay the dissolving time during the logging which also eliminated exothermic heating due to the dissolution process. For the demonstration a 900-ft deep test well with 4-in casing was used that has no connectivity with the formation. The tool was programmed to release its weight 6 hours after the start of the logging. Since the tool moves around 0.35 ft/s speed, this provided more than 5 hours of time frame for continuous recording of the pressure and temperature at the well bottom. The tool was collected from the well 6.5 hours after the deployment and the data was downloaded. As expected, the pressure stayed constant during the test. A very low-cost conveyance method was demonstrated for pressure sensor placement at the well bottom.