Casing While Drilling

Two salt dome wells successfully drilled using casing while drilling

The CWD wells used rotary steerable directional technology for deviation control and delivered significant savings over conventional offset wells.

Tommy Warren and Robert Tessari, Tesco Corp.; David Veltri, Yuma Exploration

Recent conventional wells drilled around the Chacahoula Salt Dome field in South Louisiana have been drilled directionally from central pads to preserve wetlands. These wells often encounter borehole instability and lost circulation. Some take multiple sidetracks to reach the target, and others are abandoned before reaching target depth.

Two wells were drilled with Casing While Drilling (CWD) technology in mid-2005 to depths similar to those of conventionally drilled offset wells. Both wells successfully reached the target formations. The second well delivered a 25% savings based on the average offset cost.

The CWD wells used rotary steerable directional technology for deviation control through the steeply dipping beds. Operations conducted through the casing drillstring included a plugback and sidetrack and two fishing operations for failed downhole tools. These operations were performed without tripping the casing out, showing the versatility of CWD.

BACKGROUND

Structural traps around salt domes provided some of the earliest production along the GOM coast. Reserves in smaller reservoirs are still being identified around these domes using 3D seismic and advanced logging and visualization techniques. The steeply dipping and faulted formations around the domes provide good hydrocarbon traps, but the altered tectonic stresses and complex geology make drilling the wells challenging.¹

One such salt structure is the Chacahoula Dome in Lafourche Parish, La. This dome underlies a surface area of about 8 mi², with the top of the salt slightly less than 1,000 ft below the surface at its crest. The discovery well for this structure was drilled in 1930. The area has been a continuous source of oil and gas production since then. Wells as deep as 16,000 ft have been drilled adjacent to the dome, but most wells are less than 9,000 ft deep. There are currently about 40 producing wells around the dome.