Clean-up of formate mud damage in gas wells: Lab studies and a case history Conference Paper uri icon

abstract

  • Long horizontal and multi-lateral oil and gas wells provide an attractive option for maximizing reservoir contact. Formate-based brines have been used in drilling and completion operations for more than 10 years. Advantages of these fluids include high density, solids-free brines, better compatibility with XC-polymer, starches, and less potential for formation damage. These advantages were reported in several previous publications. Filter cake of drilling fluid can act as a barrier to the fluid flow in both cased and openhole wells. Calcium carbonate particles are frequently used as weighting material to maintain the pressure that is required for well control and minimizing leak-off rate. These solid particles become consolidated and trapped in a polymeric material and this makes the filter cake a very effective permeability barrier. The conventional method for cleaning filter cake is by using solids free formate brines, either by soaking or circulating for many hours at high flow rates. This mechanical technique removes only external filter cake. Chemical means like acids, oxidizers or enzymes are usually used as an alternative method for dissolving both the external and internal filter cake. Most of these fluids cannot give a full coverage to the wellbore due to the formation heterogeneity. A new precursor (ester of an organic acid) can generate an acid downhole at a low release rate, which results in uniform fluid distribution through the wellbore. Compatibility and thermal stability tests between the precursor solution and formation brine were studied in detail. Return permeability experiments were conducted by using HPHT dynamic fluid loss cells. The ester solution was effective in cleaning the filter cake in comparison to the formate brines. A field application, where formate brine was used to drill and complete a gas producer in a sandstone reservoir is included in this paper. The gas well was drilled in a weakly consolidated reservoir, and was completed with expandable sand screens (Inconel 825). The bottom hole temperature is 300F. The produced gas contains 2-3 vol% carbon dioxide and no hydrogen sulfide. Full analysis of flow back samples indicated that most of the returned solids are calcium carbonate. Lab tests indicated that the ester solution can be used to restore well productivity by removing damage induced by the drilling mud filter cake. Copyright 2007, International Petroleum Technology Conference.

published proceedings

  • International Petroleum Technology Conference 2007, IPTC 2007

author list (cited authors)

  • Alotaibi, M. B., Nasr-El-Din, H. A., & Hill, A. D.

complete list of authors

  • Alotaibi, MB||Nasr-El-Din, HA||Hill, AD

publication date

  • December 2007