The acquisition of high-quality logging-while-drilling (LWD) cased-hole borehole sonic data in real-time (RT) and in memory (RM) dramatically improves drilling efficiency. RT sonic waveform amplitudes and slowness-time-coherency (STC) measurements enable qualitative cement evaluation either while running in hole (RIH) or when pulling-out (POOH). Operators can make appropriate decisions on cement quality to either continue drilling or perform remedial work. Data acquisition is transparent to drilling operations, removing wireline logging that can contribute to additional time and cost. Furthermore, with RM data a quantitative cement evaluation can be performed, and when environment conditions are adequate, formation compressional slownesses through casing can be computed. The advent of the latest LWD sonic acquisition technology and related processing techniques has significantly reduced the challenge of cased hole LWD sonic acquisition. More powerful sonic transmitters, improved receivers, altered transmitter-receiver spacings, and fundamental changes in tool design have meaningfully improved the acoustic signal-to-noise ratio. An improved understanding of LWD cased-hole borehole acoustic modes, the ability to transmit acoustic energies at more optimal frequencies, and the capability to simultaneously acquire cement evaluation information have all contributed to improved LWD cased-hole sonic logs. Cementing is essential to well integrity, it supports casing and provides zonal isolation. Historically, quantitative cement evaluation has been acquired via wireline (WL) tools, the most common being the cement bond log (CBL), a principle based on the amplitude of casing arrivals. LWD sonics have historically been used for top of cement (TOC) logging, which shows cement presence or absence behind casing and is a quantitative cement evaluation. Contrary to WL CBL tools, LWD tools have a steel collar that permits acoustic propagation. As such with LWD tools it has been difficult to separate casing signals from those in the tool collar (Kinoshita, 2013). In poorly bonded conditions, the casing amplitude is much larger than the collar arrival. In well-bonded conditions, the casing signal is weak and can be less than the collar arrival. From multiple cased wells in Deep Water Offshore West Africa, this paper demonstrates the application and results for the latest LWD sonic tool and processing techniques for the following; RT TOC evaluation while RIH before drilling out the casing shoeQuantitative cement evaluation from tool memory waveform dataFormation compressional slowness through casingApproximately US$450,000 saving compared to wireline runs

Congo has been an oil producing country since the 70's, it is in this context of aging oilfield and low oil price environment that a redevelopment project was launched to give a second life to a shallow, depleted, mature, offshore oilfield with viscous oil (22° API) in a cost-effective manner. The solution selected was to drill "U-shape" side tracks (inclination at TD 115deg) from the original boreholes on an existing platform (60m WD). The objective was to create a second drainage area of up to 500m, ~200m away from the original producing zone. Five re-entries U-shape wells were delivered with measured to vertical depth ratios up to 2.5 in shallow heavily depleted reservoirs (270m TVD). The team selected innovative and low cost techniques to overcome many challenges, from high DLS in unconsolidated formations using simple mud motor BHA, to running 4-1/2" liner up to 115deg inclination and implementing a thixotropic mixed metal oxide mud system to mitigate losses. The project has been successful both from a budget and production standpoint.