Detection of Drilling Loss Zones in Deep Gas Well Using Acoustic and High Precision Temperature Logging Technology, a Case Study from North of Oman

Abstract

Abstract The X-field is located in the North West of Oman. Drilling of more than 30 appraisal and development vertical wells is planned in the coming few years. Whilst drilling through the carbonate formations of Habshan, Jubaila and Tuwaiq Mountain in the existing 11 wells, total to partial mud losses were encountered in several wells due to the severe karstification. This led to significant cost increases and delays to the well delivery time. Utilizing the new wide azimuth seismic data and well maps, gives an indication of a loss zone intervals using the seismic attributes to assess the possibility of encountering the loss zone. The detection of the source of losses presents a big challenge; knowing the precise zones helps in optimizing the number of cement curing plugs thus a reduction in drilling days and cost. When losses occur; the drilling fluid moves from high pressure side (mud weight) to low pressure side (formation) causing a complete loss, where it expands rapidly and produces a turbulent flow that creates an acoustic signal and temperature anomaly. Modern acoustic logging tools, Chorus acoustic platform (Spectral Noise Log – SNL), coupled with fast and high precision temperature logging tools, Cascade thermal platform (High Precision Temperature – HPT), are capable to detect the subsequent acoustic and temperature anomalies in the drilling losses and indicate the loss zones. The chorus acoustic platform contains a new generation, high-sensitivity hydrophone – a piezo crystal element that records noise in a wide frequency range (0.1-60kHz). The Cascade thermal platform utilizes a super-sensitive platinum sensor with a response time of less than one second. The technology is already being used in critical oil and gas wells to identify tubing and casing leaks and address well integrity issues but, this is the first time it has been used in the open hole to identify the drilling mud losses in Oman. This paper presents the successful use of Chorus and Cascade platforms (SNL-HPT) in a Deep Gas well in X-Field, North of Oman, PDO Company, for identifying the total and partial loss zone across 12.25" hole. The well-A was drilled as an appraisal vertical gas deep well in one of X fields, North of Oman, and experienced fluid losses across 12.25" hole in carbonates formations. The top section was cased with 18 5/8" and 13 3/8" casings. Across the interval of interest, drill pipe was inside the borehole filled with water-based mud and the Chorus and Cascade logging tools (SNL-HPT) were conveyed by a slickline located inside the drill pipe.