Hammering Operations

Operation of the Weatherford impact hammer is based on flow rate combined with either set-down weight or pull tension to induce impact strength and frequency. A critical advantage of the impact hammer bottomhole assembly (BHA) over a conventional jarring BHA is that that no manipulation of the work string is required to actuate the impact hammer, limiting the cyclic fatigue of coiled tubing (CT). The number of trips and the trip time to cut and re-head on a new non-affected area of the CT work string are also reduced.

Jarring
Most retrieval or fishing operations using CT involve a tool or tool assembly (such as a flow-control device, packer, plug, or prong-and-lock assembly) that requires a shear force \delivered to a brass or steel shear pin or shear ring assembly. With correct weight or tension and recommended flow rates, impact forces ranging from of 20,000 lb (9,071 kg) to 32,000 lb (14,515 kg) can be achieved. Force and frequency can be manipulated by adjusting the pump rate and the set-down weight or pull tension delivered to the tools downhole, effecting a successful shear and retrieval.

Shifting
The impact hammer can be used to shift downhole sleeves for selective production well designs. Sleeves can become scale-locked, requiring an impact or vibration to break the scale from out of and around the sleeve so that it can shift as designed. Whether a sleeve is shifted open or closed, impact action can be engaged or initiated by the impact hammer with flow-activated shifting tools. Once the sleeve is shifted, the tool releases. Running back down into and through the sleeve area confirms whether the shift was successful. Most applications require a higher-frequency vibratory impact action rather than a high-load, lower-frequency impact.

Broaching and Rupturing
Scale, asphaltine, and paraffin can precipitate and accumulate on the wall of the tubing or casing. Special cutting and impact mill designs used with the impact hammer allow for mechanical breakup and simultaneous application of chemical treatments to accelerate the breakdown of the residual deposits. For completions that require ceramic disk assemblies, a hardened-steel, cone-shaped impact head effectively impacts and shatters the disk to open the flow path.