Acquiring Real-Time Data in Under Balanced Coiled Tubing Drilling for Geosteering: The Current Success and Factors Limiting Physics Boundaries

Abstract

Abstract The objective of this article is to share the current success of real-time logging while drilling (LWD) data acquisition in under balanced coiled tubing drilling (UBCTD) that enables petrophysical evaluation and precise depth control in identifying layers targeted for geosteering a well. In addition, the paper will generally discuss the trial results of technologies tested in UBCTD operations, the success and limiting factors. A future outlook to acquire more advanced logging technology to assist a precise geosteering are discussed later as challenges for further development in UBCTD The method of tool testing procedure and analysis of the acquired data addressed the then current tools potential and, in some cases, directed the research towards the improvements required before the tool is operationally viable for further testing. The tools trials were conducted in multiple environments from controlled to simulation of the actual UBCTD conditions. In most of the cases, an ideal environment was created to acquire the desired data in order to prove the viability of the concept. The data acquired from the trial runs are treated carefully to avoid missing information and overlooking of the hidden potentials. UBCTD conditions challenged the current LWD tool physics especially for porosity measurements due to a couple of factors, such as the borehole size and the multiphase condition of fluids used in the process. With the aim of assisting geosteering in complex environments, multiple conceptual tools were tested in UBCTD in attempt to acquire LWD data. The tested LWD tools are GR, Acoustic and Resistivity where the trial was simulated in a real coiled tubing drilling environment. Such tools consist of a set of devices dedicated to obtain certain measurements, these are developed for Gas/Water velocity measurement; electrical/resistant probes for water holdup and optical probes for gas holdup; and pulsed neutron. The aforementioned tools were tested in controlled environments to prove the concepts. There were mixed results indicating that there are real challenges associated with developing LWD for UBCTD The value of sharing these trial tests is to ensure the concepts and practicality for developing a logging tool are captured before proceeding to tools manufacturing. Some concepts are mere theories therefore require further enhancements to be viable before the actual LWD tools were built. Sharing such information could help the industry to focus on certain critical aspects in developing super slim LWD tool in the ever-growing UBCTD operation in future.