A Novel Solid Inhibitor for Anhydrite Scale Control Under Extreme Well Conditions

Abstract

AbstractThe formation and deposition of mineral scale can detrimentally impact production rates and affect the overall well performance during oil and gas production. This is especially challenging in HTHP stimulation treatments where compatibility of the scale control chemical with fracturing fluids is critical, and longer-term inhibition performance is desired. A new solid inhibitor was developed for this purpose and applied in multiple wells in the Eastern offshore basin of India to combat mineral scale within the proppant pack and production tubing over the long term, under extreme downhole conditions (T= 400°F, P=13,500 psi). Neither downhole chemical injection mandrels nor surface treatments can adequately control scale deposition under these conditions, spurring the need for a longer-term inhibition program for these wells.A liquid scale inhibitor with excellent inhibition performance and good compatibility with various fracturing fluid systems at high temperature was first identified. The new solid inhibitor product was made by adsorbing the scale inhibitor onto a high-strength, proppant-sized substrate with a large surface area. The substrate is synthesized using nanotechnology, to prevent any possible conductivity loss under high formation closure pressure. Various chemical modifications were made to this adsorbed solid inhibitor to prevent excessive inhibitor release during early stages of production, resulting in a longer-term scale protection. This modification allows the solid inhibitor product to be completely compatible with the fracturing fluid.Scale modelling indicates that the wells treated have a severe anhydrite scale problem under downhole conditions. The results of comprehensive laboratory testing show the new solid inhibitor can prevent anhydrite scale up to 400°F, and is completely compatible with zirconium- crosslinked fracturing fluid at 350°F and above. To date, six fracture treatments have been performed by using a total 23,800 lbs of this new solid inhibitor. The wellhead water samples are being collected for scale inhibitor residuals analysis, as the wells start to produce water. The residuals data review and comparison with laboratory-derived data are discussed in this paper.Adding scale inhibitors to a fracturing fluid has been a well-established practice to provide long-term inhibitor protection during hydrocarbon production. However, to ensure compatibility of the inhibitors with high-temperature fracturing fluids, especially metal based cross-linked fracturing fluids, without compromising the inhibition longevity at high pressure and temperature remains a stiff challenge. The new approach described here meets this objective, extending the long-term well performance under HTHP conditions.