Surfactant-Based Fluid-Loss Pills for ZnBr-Based High-Density Completion Fluids and High-Temperature Applications
- Ahmed M. Gomaa (Baker Hughes Ltd) | Jennifer Cutler (Baker Hughes) | Qi Qu (Baker Hughes) | Kay E. Cawiezel (BP America Production Co.)
- Document ID
- Society of Petroleum Engineers
- SPE European Formation Damage Conference & Exhibition, 5-7 June, Noordwijk, The Netherlands
- Publication Date
- Document Type
- Conference Paper
- 2013, Society of Petroleum Engineers
- 1.7.5 Well Control, 5.4.10 Microbial Methods, 2.4.5 Gravel pack design & evaluation, 5.3.4 Integration of geomechanics in models, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.6 Drilling Operations, 1.8 Formation Damage, 2.4.6 Frac and Pack, 2.4.3 Sand/Solids Control, 2.7.1 Completion Fluids, 2.2.3 Fluid Loss Control
- Surfactant-Based Fluid, Fluid Loss Pills, Znbr2-Based
- 1 in the last 30 days
- 243 since 2007
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Excessive loss of high-density brines into the formation has always been a major concern during completion operations, since it is uneconomical and leads to formation damage and well control issues. A viscoelastic surfactant (VES) system was introduced as an alternative for polymers because of high-temperature instability, incompatibility problems, and the necessity of acid cleanup for the polymer-based system. However, past literature documented that VES systems were limited to only CaCl2/CaBr2 brines due to the negative effect of ZnBr2 solutions on the surfactant's ability to form gel which limits the applicable density for past fluid-loss pills. This paper introduces improved fluid technology that uses nanoparticles and new low molecular weight surfactants to effectively control fluid-losses for high-density brine that contains ZnBr2 at high temperature application.
Laboratory studies were conducted to examine the effect of the VES system on controlling leak-off rate using a HP/HT fluid-loss cell. The apparent viscosity of the VES solution was measured as a function of shear rate and temperature (up to 300°F).
Based on experimental results leak-off of surfactant based fluid is controlled by the elastic structure of the surfactant micelles. The strong elastic structure of gel will not deform to pass through the pores, it will plug this pores and eliminate any flow of the solution. Therefore, surfactant-based pill developed long-term stability as it tested for 7 days with a noticeable decrease in the leak-off rate with time. Optimum surfactant concentration does not depend on the brine composition or formation permeability but it was mainly dependent on temperature.
A breaker based on mineral oil caused a smooth viscosity decline while a breaker based on mutual solvent had a rapid viscosity decline. For mutual solvent, viscosity was instantaneously reduced by 50 to 90% depending on brine composition, surfactant concentration and temperature. However, temperature has most significant effect.
Excessive loss of high-density brines into the formation has always been a major concern during completion operations because it is uneconomical and leads to formation damage, hole collapse and well control issues. Typically, the fluid-loss control pills are composed of very high concentrations of crosslinked polymers. The sealing mechanism of these pills is a combination of viscosity, solids bridging, and polymer filter-cake buildup on the porous rock. Due to the instability of polymers at high bottomhole temperatures, incompatibility with some divalent brine, and the necessity to cleanup with acid, a new solids-free lost-circulation pill that is stable in a high-salt environment should be developed.
Polymer systems are very effective in fluid-loss control as long as the temperature limit of the specific polymer is not exceeded. Studies with particulate systems in polymers showed irreversible plugging, which negatively influences the productivity or injectivity of the given zone. It has been reported that xanthan gum pills on Berea sandstone cores yielded less than 10% regained permeability (Himes et al. 1991). Hydroxyethylcellulose (HEC) is well known for its low residual content, but even at 14 to 18 kg/m3, it will not form a compact filter cake if the formation permeability is higher than 20 mD (Parlar et al. 1996; Vitthal and McGowen 1996). Normally, HEC polymer solutions are difficult to crosslink and do not form rigid gels. They control fluid loss through viscous drag force and gradual filtration. Hence, these fluids penetrate deeper into the formation than the crosslinked fluids and can cause severe permeability damage. The retained permeability for non-crosslinked HEC is typically in the 30% to 50% range (Hodge et al. 1995; Parlar et al. 1996).
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