摘要
For several decades, wells drilled in Block 6, Sudan, have experienced serious hole-instability problems related to drilling fluids due to the highly reactive and dispersive shales that exist in the Aradeiba and Abu Gabra formations. These problems included washout hole sections combined with tight holes, as well as serious sloughing. Frequent wiper trips were required and logging of the wells was not usually successful. Previously, several conventional inhibitive water-based drilling fluids such as KCl/polymer, KCl/lime/polymer and KCl/PHPA （partially hydrolyzed polyacrylamide） have been used in this area, but with only marginal improvements in hole stability and drilling performance. Recently, a newly formulated KCl/sodium silicate system, which is characterized by the good rheological properties and filtration control, was developed and used for providing the necessary inhibitive character. The first trial well was drilled with this kind of drilling fluid in Block 6, Sudan, and the following benefits were observed： （1） Excellent integrity exhibited by drilled cuttings for shale formations; （2） Stable borehole kept with lower mud weight; （3） Reduced wiper trips; and （4） In-gauge borehole shown from caliper logs. Later on, five more wells were drilled with the KCl/sodium silicate system in this area. It was found that the KCl/sodium silicate system can fully meet the demands of drilling operations in this area. Case studies are presented in this paper in terms of wiper trips, inhibitive character of cuttings, hole conditions and mud weight.
For several decades, wells drilled in Block 6, Sudan, have experienced serious hole-instability problems related to drilling fluids due to the highly reactive and dispersive shales that exist in the Aradeiba and Abu Gabra formations. These problems included washout hole sections combined with tight holes, as well as serious sloughing. Frequent wiper trips were required and logging of the wells was not usually successful. Previously, several conventional inhibitive water-based drilling fluids such as KCl/polymer, KCl/lime/polymer and KCl/PHPA （partially hydrolyzed polyacrylamide） have been used in this area, but with only marginal improvements in hole stability and drilling performance. Recently, a newly formulated KCl/sodium silicate system, which is characterized by the good rheological properties and filtration control, was developed and used for providing the necessary inhibitive character. The first trial well was drilled with this kind of drilling fluid in Block 6, Sudan, and the following benefits were observed： （1） Excellent integrity exhibited by drilled cuttings for shale formations; （2） Stable borehole kept with lower mud weight; （3） Reduced wiper trips; and （4） In-gauge borehole shown from caliper logs. Later on, five more wells were drilled with the KCl/sodium silicate system in this area. It was found that the KCl/sodium silicate system can fully meet the demands of drilling operations in this area. Case studies are presented in this paper in terms of wiper trips, inhibitive character of cuttings, hole conditions and mud weight.
