Schlumberger

CHDT Cased Hole Dynamics Tester

Single-trip formation pressure testing and fluid sampling in cased wells—with pressure integrity restored

The CHDT cased hole dynamics tester conducts multiple pressure measurements and collects fluid samples behind the casing in a well. In a single trip, the CHDT tool can

  • drill through a casing and into the formation
  • perform multiple pressure measurements
  • recover fluid samples
  • effectively plug the hole made in the casing to restore pressure integrity.

Streamlined formation access in cased holes

The drilling efficiency of CHDT operations is a significant improvement over traditional cased hole formation testers, which rely on explosve charges to penetrate the casing and cement in order to establish communication with the formation. The explosive shock often compromises the seal between the tester and the casing to prevent obtaining valid pressure measurements, conducting pretests, or sampling fluids. Any pretests are difficult to analyze because the penetration depth of the explosive charges is uncontrolled.

CHDT drilling eliminates the use of explosives to minimize damage to the casing, cement, and formation and to accurately control penetration depth. Drilling also reduces formation skin damage and can reach beyond the invaded zone into the formation.

The innovative CHDT tool seals against the casing and uses a flexible drill shaft to penetration through the casing and cement and into the formation. As the drill progresses, a built-in instrument package simultaneously monitors pressure, fluid resistivity, and drilling parameters for real-time quality control of the operation. Following testing and sampling, a corrosion-resistant plug is used to seal the hole in the casing. The mechanical metal-to-metal seal is rated to a differential pressure of 10,000 psi to eliminate the need for remedial casing repair or a cement squeeze.

Critical data for unstable wells or locating bypassed hydrocarbons

Where wells experiencing difficult openhole conditions must be cased before testing and sampling can be conducted, the CHDT tool provides otherwise unavailable pressure and fluid data from behind the casing. In older cased wells, old or incomplete logging data can be enhanced to optimize recompletion plans, assess unknown pay zones, and evaluate wells for economic potential.

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Limiting Pressure Drawdown Controls Shock Effects

The CHDT station log shows the pressure response (blue) during a low-shock sampling job. The log also details the pumpout volume response (gray).
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