Effective High-Density Wellbore Cleaning Fluids: Brine-Based and Solids-Free
- Paul H. Javora (BJ Services Company) | Glenn David Baccigalopi (BJ Services Company) | John R. Sanford (ENI International Resources Ltd) | Cristina Cordeddu (Eni Petroleum Co. Inc.) | Qi Qu (BJ Services Company) | Gary Lane Poole (BJ Services Co. USA) | Bernard M. Franklin (BJ Services Company)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 2008
- Document Type
- Journal Paper
- 48 - 54
- 2008. Society of Petroleum Engineers
- 4.2.4 Risers, 2.7.1 Completion Fluids, 2.4.3 Sand/Solids Control, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.14 Casing and Cementing, 1.2 Wellbore Design, 2 Well Completion, 3 Production and Well Operations, 4.2.3 Materials and Corrosion, 1.11 Drilling Fluids and Materials, 1.6 Drilling Operations, 1.8 Formation Damage, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation
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Displacing drilling mud with clear solids-free completion brine is a critical step during well completion. As we move into deeper waters and drill to deeper depths (greater than 25,000-feet MD), conventional methods and cleaning fluids become a limiting factor in this phase of the operation. Conventional cleaning fluids use fresh water or seawater treated with surfactants to remove wellbore solids and water-wet tubulars. Using low-density cleaning fluids creates a negative differential pressure between the working kill weight fluid and the formation, casing, and cement liners. In many situations, the negative differential pressure cannot be tolerated, and the risk of failure at the liner top, etc., is increased—especially, if the wellbore has not been pressure-integrity tested. Additionally, with increasing rig/spread costs, high pump rates are necessary to decrease the time it takes to perform these operations. The pump rate is indirectly proportional to the pump pressures required. Weighted spacers decrease the overall pressure differential, which allows for higher pumping rates.
To overcome the density limitation of these cleaning fluids, conventional techniques, such as additional hydraulic horsepower, backpressure schedules, the addition of solids to lighter cleaning fluids (e.g., water, seawater), or balancing the weight of the low-density cleaning fluid with a matching higher-density fluid is used. However, each of these "fixes?? has inherent limitations and is accompanied with reduced cleanup efficiency. Furthermore, conventional surfactants are not active or effective in high-density brines. New brine-compatible surfactant chemistry and the corresponding balanced-displacement engineering design were developed to overcome limitation of conventional displacement technology.
This paper describes the field applications of new brine-based, high-density, solids-free cleaning fluids in balanced-displacements in deepwater and offshore shelf wells. The new high-density fluids were based on new surfactant technology developed to ensure effective wellbore cleaning, wellbore design parameters, and displacement modeling. In addition, weighted spacers aid in reducing high pump pressures and wellbore pressure differentials. In one case history, a maximum pumping pressure of more than 9,000 psi was expected for conventional water-based displacement but was reduced to a little more than 3,000 psi with the new design. High-density cleaning fluids, with densities up to and greater than 17.5 ppg, have been formulated and used successfully without compromising cleanup efficiency and significantly reducing differential pressures. Results from laboratory development and field applications are presented.
Completing today's challenging wells demands the utmost care and attention to the process of displacing drilling mud or drill-in fluid with clear completion brine. Failure to properly complete the displacement process can lead to significant complications in subsequent completion and tool operations, contribute to increased formation damage, and increase the cost of the completion.
Krause (1986) presented an overview of important requirements for successful displacements that included the predisplacement mechanical and chemical conditioning of the mud; mechanical scraping of the casing, spacers, chemical washes, pipe rotation, and reciprocation during displacement; and various displacement scenarios. In addition to mechanical scrapers, other tools (Saasen et al. 2004) currently in use include brushes, magnetic subs, circulation subs, and junk baskets, in one form or another. All of these tools are a necessary part of a current displacement toolkit.
Displacement success is complicated by the fact that pipe in the wellbore is not concentric (Dutra et al. 2005; Frigaard and Pelipenko 2003), but exhibits a wide range of eccentricities. Pipe movement, reciprocation, and rotation are key remedies that are always desired during mud conditioning—especially in highly deviated wells—but may not be possible for certain displacements, such as deepwater displacements involving a large riser section or for highly deviated wellbores. Without being able to move pipe under these circumstances, an extra strain is placed on the capability and efficiency of chemical wash spacers, which are then required to have enhanced cleaning activity toward the target mud. Pumping the displacement spacer system in turbulent flow (Dutra et al. 2005; Brand et al. 2001) throughout the displacement process contributes to improved spacer system performance.
Another more recent factor in determining displacement success involves the base oil and chemical makeup of current-day synthetic oil-based muds (SOBM) (Berry 2005). To comply with environmental constraints and the demands of deepwater and high-temperature high-pressure (HT-HP) wells, new emulsifier and viscosifier packages were developed to stabilize these SOBM. In effect, these enhanced SOBM are significantly more difficult to break and displace from the wellbore than are traditional muds. As a result, new chemistries for chemical wash spacers have been developed and implemented in the field (Berry 2005; Berg et al. 2002).
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Baccigalopi, Glenn, et.al. 2005. Guidelines for Displacement of Synthetic,Oil and Water Based Muds and Drill-In Fluid Systems, Internal Document, BJServices Corporation, 2005.
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Krause, D.C. 1986. Solids-FreeBrines: Efficient Displacement Techniques Can Save You Money. Paper SPE14830 presented at the SPE Formation Damage Control Symposium, Lafayette,Louisiana, 26-27 February. doi: 10.2118/14830-MS
Saasen, A., Svanes, K., Omland, T.H., Mathiassen, E., and Vikane, O. 2004.Well Cleaning Performance.Paper SPE 87204 presented at the IADC/SPE Drilling Conference, Dallas, 2-4March. doi: 10.2118/87204-MS