Geohazards have a direct impact on the drilling and completion of wells; they present safety risks and are costly. They can be caused by formation properties such as overpressure and can be associated with geological structures such as faults and salt bodies. Critical to drilling success, seismic data provide information used to construct an Earth model consisting of 3D structural depth images showing geological targets or hazards and formation properties relevant to drilling such as pore pressure. However, predrill estimates of structural depth images and formation pressures typically have large uncertainties, which elevate safety concerns and drilling risks and could increase the cost of wells. This risk is especially problematic in challenging environments such as deep water, where rig rates are high and continue to increase.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA new technique provides conventional borehole seismic measurements in real time while a well is being drilled. The system consists of a logging-while-drilling (LWD) tool with seismic sensors positioned near the drill bit, a seismic source at the surface, and a measurement-while-drilling (MWD) system for real-time telemetry. The seismic source is fired during pipe connections, seismic data are processed downhole and check-shot information is sent to the surface.Borehole seismic tools conveyed by wireline cable have been used for a variety of applications including seismic timedepth mapping, and reflection and transmission imaging of subsurface structures. Although wireline borehole seismic services are mature, they are unable to provide all the benefits that are sought in real time while drilling. This is particularly the case when borehole seismic surveys are conducted to help make drilling and well construction decisions, such as steering and deciding on casing and coring points. The new service provides standard borehole seismic information in real time that can be exploited for drilling optimization, cost savings, and safety improvements. Check-shot (time/depth) data are used to place the bit on the seismic map to help well navigation and casing point selection and to avoid drilling hazards, such as pore pressure, seen on the seismic. Real-time seismic velocities can be used to update pore-pressure predictions from surface seismic. Ultimately, the real-time velocities will be combined with look-ahead images, formed from the seismic reflections from horizons ahead of the bit, to provide a direct measurement of the distance to a marker of interest.In 2000, a field-test campaign conducted with experimental tools in the Gulf of Mexico demonstrated the first known real-time check-shot technique with an LWD tool. We will show the results and further describe the status of the service.
The scope of the paper is to introduce the application of a new wireless downhole real time telemetry tool and its applications in three different deepwater completions operations. The main method to explain the technology application is through three case histories. In two of these case histories, the availability of downhole real time data led to actions on the surface that ensure the positive outcome of the operation. In the third one, the continuous monitoring of well conditions increase the safety and efficiency aspect of the operation. Another approach used in the paper to validate the technology is the comparison of the field real time data with the expected behavior predicted by the modeling done before the operation. In the fracpack case, pipe contraction due to cooling led to the application of unexpected additional weight on surface. The quantification of different contraction ratios versus temperature drop can help understand the relative movement during operations of downhole tools. In the second case, in the multi-zone single trip system (MZST), the downhole weight transmission monitoring was able to quantify weight transmission at different times of the operation, as expected when the inner string of the tool was inside the outer and permanent string of the system, according to the tubing movement analysis buckling was minimum. In the fluid loss control case, fluid level drop in real time, allowed the determination of fluid loss rate in-situ and secure the well control aspect of the operation immediately after perforating gun (TCP) firing and after an acid frac job. The control of the losses by an optimum overbalance, minimize fluid control losses and reservoir damage. The case histories will show the direct benefits of the technology in well control and productivity, in the completions operations like TCP, fracpack and MZST.
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