Sensor Ball: Autonomous, Intelligent Logging Platform

Recent developments in automation and electronics have enabled modernization and miniaturization of oilfield instruments. One product of these trends is our autonomous logging platform called "Sensor Ball". The Sensor Ball is a handheld, untethered logging tool that one person can deploy and recover from a pressurized well with no special equipment and crews (Deffenbaugh, 2016). The only tool needed is a wrench to open the cap of the wellhead. The operator puts the sensor ball in through the cap, then sequentially opens and closes the crown and master valves. This process takes only a few minutes. Once clear of the well head, the Sensor Ball falls down the well, logging data as it travels downhole. During this time, all the wellhead valves are closed and there is no need for the field crew to stay at the well site. We present data from recent Sensor Ball deployments to log pressure and temperature profiles and bottom-hole pressures. Depth information is provided by a novel onboard sensor that detects the connections between casing or tubing joints like a casing collar locator. A small dissolvable metal weight is magnetically attached to the housing and is sized to make the Sensor Ball descend at about 1 foot per second. At the desired depth, Sensor Ball drops the weight to become buoyant in the wellbore fluids and return to the surface. As it returns, it repeats the logging measurements, storing temperature and pressure data in its internal memory. After a typical four-to-eight hour mission, the operator returns to the well, opens and closes the well head valves in reverse order, removes the cap and takes out the Sensor Ball. The logged data are downloaded wirelessly to a laptop or cell phone. A lightweight, syntactic foam housing provides buoyancy and protects the electronics from the well fluids. The small thermal mass of the housing minimizes the temperature distortion in the downhole environment. This miniaturized technology simplified logging to a one-person job and shortened the time at the well from multiple hours to a few minutes. This work describes a novel method of retrieving downhole data, which is a practical and inexpensive alternative to wireline or slickline logging and permanently-installed sensors (Deffenbaugh, 2017). In this paper we present the system design and our recent field results from vertical and deviated wells. We also describe a new application of the Sensor Ball where we perform extended bottom-hole pressure measurements in addition to logging temperature and pressure along the wellbore.