Apparatus and method for fastening and positioning of LWD sensors for azimuthal measurements.
Publication Date: 2005-Jan-17
The IP.com Prior Art Database
1) During the LWD process, different operational conditions are leading to several dynamic reactions of the bottom hole assembly (BHA)and its subassemblies, such as azimuthal formation evaluation sensors. One of the most common reaction is a change in rpm caused by tick slip. An onther reason for changes in rpm during the drilling or logging process could be the deliberate reduction or increasement of rpm by the operator to react on undesireable dynamic behaviours of the BHA such as vibration, bit bouncing, etc., or to influence the rate of penetration (ROP), even by adding mud motors to increase RPM . In case of conventional drilling in slide mode or during the Logging while tripping processes (LWT), the drill string rotation migth be even stopped completele. Thus, the scope of possible RPM is from sero to several hundred revolutions per minute. Many azimuthal formation evaluation principles are requirering a permanent revolution of its sensor or sensors. To optimize the measurement, it might be even beneficial to have a constant rpm with small or no changes. This invention is about the use of a sensor carrier device, which is uncoupled from the drillstring and independently driven from the drill string rpm. It would fullfil and improve the above requirements. 2) An additional application to be considered is wire-line operation. Normally, wire-line is purely performed in slide mode, which means no rotation of the sensors. A draw back of this way of operation is a not full-circumferencial scanning of the borehole wall or near bore hole formation. Comon praktise to cover as much of the circumference of the borehole is to use several sensors on the circumference of the tool. Even such an arrangement will leave a portion of the borehole wall area unsampled. This portion is increasing with bigger hole sizes. An uncoupled, self driven sensor-carrier as described above would solve and improve such wire line services as well.