New HF Acid System Improves Sandstone Matrix Acidizing Success Ratio By 400% Over Conventional Mud Acid System in Niger Delta Basin

Abstract Matrix Acidizing has been used as the preferred method of stimulating hydrocarbon producing wells in the Niger Delta Basin. The majority of reservoirs in this area are Sandstone reservoirs. Conventional Mud Acid system has been the main HCl:HF acid mixture used in restoring or improving the productivity of these sands. A combination of rapid spending with clays and silicates, matrix unconsolidation in the near wellbore area and subsequent precipitation of various acid reaction by-products has limited the usefulness of Mud Acid for matrix stimulation treatments in this area. Various attempted solutions using existing fluoboric acid systems and in-situ HF generated acid mixtures have been tried with mixed results. Using statistical data gathered from over fifty wells stimulated with Mud Acid, a major operating company in Nigeria rated the results of these treatments as less than 20 percent, successful in 1997. A New HF Acid System has been successfully applied on more than thirty wells over the last two and a half years. Field results using the New HF Acid System demonstrate a remarkable increase in the success ratio (greater than 400%) over conventional Mud Acid formulations. Consistent extension in the time to return to pre-treatment production rates has been observed. An increase of 350% in the incremental hydrocarbon production, using the New HF System, has been recorded over results with Mud Acid on the same drainage points. Notable matrix acidizing cost reduction of 25% and a drastic payback time reduction (500%) based on a $12/bbl crude, has been noticed since the New HF System was introduced in the Niger Delta basin. Actual candidate selection criteria, job design, technical and economic performances evaluation, and the laboratory analysis of core samples from the sands stimulated with this new HF system, have been included in this paper.