Completion Fluids Challenges in Maximum Reservoir Contact Wells

Abstract

Abstract Most drill-in fluids contain weighting solids. The overbalance required between the drill-in fluid and reservoir to keep the well under control will force the weighting solids to enter the formation and cause damage, Bailey et al. (1999). Horizontal wells are intended to maximize reservoir drainage and minimize water production due to water conning, Beal et al (1996). However, unlike vertical wells, poor acid distribution occurs during matrix acidizing. Coiled tubing cannot reach the total depth of the well because of some limitations such as large washouts, length of the reel and diameter of the coil, which makes acidizing horizontal wells non-effective, (Nasr-El-Din et al., 2004b). In addition, conventional weighting solids used in drill-in fluids when entered the reservoir formation will not easily flow back into the wellbore when production resumes, Bailey et al. (1999). Format drill-in fluids with low solids content can then be used in horizontal wells, Simpson et al. (2005). However, they are expensive and require close monitoring of the pH, Nasr-El-Din et al. (2004a). Formation damage from all drilling fluids are still a concern and they are more problematic in horizontal and maximum reservoir contact wells and their damage require chemical and mechanical removal methods. Cleanup of drilling-fluid filter cake in long horizontal and multilateral wells is a difficult task. Both mechanical water jetting and/or circulating new volumes of low solids drilling fluids have certain limitations. Other methods of removing filter cake such as using chemical means for example mineral acids, esters, oxidizers, chelating agents, viscoelastic surfactants and enzymes are also limited at certain conditions. Intensive lab work has been done to evaluate mechanical and chemical methods in removing formation damage induced from drilling fluids. However, no work was done before to the best of author's knowledge in comparing these removal methods (mechanical and chemical) for different drill-in fluids supported with field cases to provide guidelines on when to use or avoid. The paper will review chemical means used to remove filter cake. Limitations of each method are highlighted. Implications to the field are discussed. Introduction Ezzat (1993) showed the requirements for water-based drill-in fluids for horizontal wells such as physical stability, cutting transport, lubricity and formation damage control. The hydrostatic pressure of the drill-in fluids must be high enough to control the formation pressure but not too high to avoid fracturing the formation and losing circulation. Using bridging materials are important to minimize filtrate invasion, minimize fine migration and improve hole stability. In deviated wells, cutting accumulation and settling while drill-in fluids in static motion is a big concern. The drill-in fluids should have good rheological properties to prevent solids and cuttings settling. He also mentioned that core flood testing is important to evaluate drill-in fluids formation damage as well as lab evaluation at reservoir temperature and pressure.