RIASSUNTO
Abstract
Recent conventional wells drilled around the Chachaloula Salt Dome field in South Louisiana have been drilled directionally from central pads due to wetland environmental issues. These wells often encounter borehole instability and lost circulation drilling problems. Some take multiple sidetracks to reach the target and others are abandoned before reaching the intended target depth.
Two wells were drilled with Casing while Drilling (CwD) technology in mid-2005 to depths similar to 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 utilized rotary steerable directional technology for deviation control through the steeply dipping beds. Operations conducted through the casing drillstring included a plug-back and sidetrack and two fishing operations for failed downhole tools. These operations were performed without tripping the casing out, thus showing the versatility of the CwD technology.
Introduction
Structural traps around salt domes provided some of the earliest production along the Gulf of Mexico coast.
Reserves in smaller reservoirs are still being identified around these domes using 3-D seismic and advanced logging and visualization techniques. The steeply dipping and faulted formations around the domes provide good hydrocarbon traps, however the altered tectonic stresses and complex geology makes drilling the wells challenging.1
One such salt structure is the Chacahoula Dome located in Lafourche Parish, LA. This dome underlies a surface area of about eight square miles 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 production of both oil and gas since that time, with sporadic drilling activity continuing until today. Wells as deep as 16,000 ft have been drilled adjacent the dome, but most wells are less than 9,000 ft deep. There are currently about 40 producing wells around the dome.
The dome is located in a marsh area (Fig 1) where drilling locations are limited due to environmental considerations. Most of the current drilling is conducted from pads adjacent existing roads to minimize the
environmental impact.