Foam cementing has been widely used for offshore applications where the formation has low fracture gradients, and shallow water flow may occur. One challenge of foam cementing is to ensure that the foamed slurry is stable at the desired foam qualities with low permeability. Therefore, stabilizers are commonly applied along with the foaming agent. This paper describes the comparison testing and several offshore applications of a new liquid foam stabilizer that improves logistics and flexibility on the rig, and prevents excessive viscosity and foaming during mixing. The new liquid foam stabilizer was tested in the laboratory to compare its performance with that of a dry stabilizer used previously in the field. The stabilizer was then used in several offshore wells to assess its performance in real-world operations. In particular, one problem with dry foam stabilizers is that they can promote excessive foaming during mixing, which leads to pump cavitation if not controlled with a defoaming agent. The field operations were arranged to test a new operational procedure for use with the liquid foam stabilizer to avoid cavitation without a defoamer. The laboratory testing determined that the new solids-free liquid foam stabilizer disperses easily in the cement slurry. The new stabilizer was also found to improve the stability of the foam and the density distribution of the set foam cement compared with no stabilizer. Furthermore, several case histories will demonstrate that the combination of the liquid additive and the new operational procedure improved the slurry mixability without any pump cavitation issues. The new liquid foam stabilizer has more predictable and reliable response than conventional dry stabilizers, and the case histories will demonstrate how its use improves cementing flexibility and logistics.
A new pulsed eddy current (PEC) - electromagnetic (EM) based tool called the enhanced Pipe-thickness Detection Tool (ePDT) has been introduced for multiple pipes’ corrosion inspection. The tool can measure the metal wall thickness of five concentric pipes with the maximum outer diameter (OD) up to 26". This capability and ePDT's unique configuration provide the most advanced downhole solution for tubular evaluations of production, injector and gas/oil storage wells. The ePDT features a 2" (51mm) OD with ratings of 350°F (175°C) and 20,000 psi (138Mpa). The innovative sensor of ePDT incorporates: (1) A fractal transmitter (TX) coil array that improves the tool's performances with enhanced signal-to-noise ratio (SNR) covering a wide signal dynamic range, and adaptability for various logging speeds and spatial resolutions for varying pipes; (2) A synthetic aperture of the receiver (RX) coil array for noise compensation from extraneous tool motion; (3) A wide-spatial aperture RX coil array which when combined with (1) and (2) allows for compressing the inner pipe remnant magnetization interferences without sacrificing spatial resolution; (4) A "shallow" measuring transducer to detect EM properties for logging data corrections. The results from lab tests and field trials combined with simulation indicate that the ePDT can quantitatively measure 5 pipes from 2-7/8" as the smallest tubing to the maximum outer casing with the OD of 26". In addition, the logging speed can be significantly increased compared to previous generation tools.
Deepwater drilling and cementing have been a challenge due to the low temperature at seabed, low fracture gradients, shallow water flow, gas hydrates, etc. Foamed cementing is one of the best practices that have been used for deep water wells. Dry foam stabilizers have been used but are limited to the number of jobs achievable with pre-blended cement on the rig. Introducing a liquid foam stabilizer improves logistics and flexibility, so one type of cement can be used for all cementing jobs, including primary and remedial jobs. In this study, the performance of the novel liquid foam stabilizer was thoroughly evaluated with different types of cement and mixing fluid at various temperatures. API class H or class G cement with a foaming agent and the new foam stabilizer were mixed with fresh or sea water at different densities. The salt tolerance of the liquid foam stabilizer was investigated by adding a variety of salts at different concentrations. This liquid foam stabilizer also was evaluated at different concentrations and different foam qualities. The evaluation includes foam stability and density distribution of set cement. Both the set and unset foam stability were tested. The test results show that the liquid foam stabilizer significantly improves the foamed slurry stability and the density distribution of the set cement. The new liquid foam stabilizer helps foamed slurry and set cement stability with different types of cements, with fresh and sea water at temperatures from 40 to 190°F. In addition, it helps to improve system flexibility and logistics. Land and offshore applications of the new liquid foam stabilizer will also be described in detail.
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