A Soft Rock Project was conducted by Amoco Production Company and Elf Aquitaine on the Texas Gulf Coast in June and July 1990. The purpose of the project was to demonstrate and gain experience in slim hole continuous coring and drilling in soft sediment formations. Four wells were completed, which included two planned sidetracks. A total of 1670 ft was continuously cored and 1018 ft was full hole drilled. Both 4-3/8 in. and 3-1/16 in. hole sizes were cored/ drilled.
Slim hole continuous coring and drilling were suc-cessfully conducted in recent age sediments (Tertiary). It was determined that the most, important factor affecting wellbore stability was keeping the flow regime in laminar flow. Lost circulation in unconsolidated sands was controlled by using calcium carbonate and starch for fluid loss control. Modified face-discharge core bits used with a split tube core barrel assembly were the most effective in recovering core. Setting cement plugs and sidetracking were accomplished and open hole logs were successfully run in the slim holes.