Investigation on Fouling During Application of EOR Polymer in Aishwarya Field

Abstract Deposition of elastic fouling material on equipment for processing and transportation of crude was observed after EOR polymer breaking through to producing wells of the Aishwarya field. The objective of the study included analyzing polymer containing deposits, concluding on mechanism of precipitation and developing the solution for fouling control based on the novel laboratory test procedure. Aishwarya field is in north-west part of India. Fatehgarh group is the main reservoir unit. Artificial lift in Aishwarya is mainly by ESP. An opportunity to improve the recovery of Aishwarya field via better displacement of oil was envisaged through implementation of EOR polymer flood. HPAM (partially hydrolyzed polyacrylamide) polymer injection was initiated in September 2017. Failures of ESP pumps, significant fouling of strainers of liquid transfer and PWRI pumps, pressure increase in Aishwarya production line which necessitate increased pigging frequency was observed soon after polymer breaking through to producing wells. Detailed analysis of produced water containing back produced polymer and elastic deposits collected from different equipment were performed. Specific test methods have been selected for such analysis including SEC, XRF, XRD, SEM/EDS, FTIR, NMR etc. It was found that Aishwarya deposits contain high concentration of precipitated polymer (to 36%) and polymer was completely hydrolyzed, degree of hydrolysis or DOH at 100%. Chemical nature of polymer was evaluated as Calcium Carboxylates. DOH of returned polymer in Aishwarya produced water was measured upto 79%, significant increase from the initial 25%. Such high DOH significantly dropped tolerance of HPAM to divalent cations and increases potential for precipitation with Calcium in Aishwarya brine having relatively high concentration of Calcium and high value of the relative hardness, the ratio of divalent cations to total cations. Fast increase of DOH was attributed to the relatively high temperature of the Aishwarya reservoir (up to 77 deg C at the OWC zone). Novel test method, accelerated aging test, has been used to investigate the long-term stability of the applied HPAM and more thermally stable polymers containing monomers of acrylamide tertiary butyl sulphonic acid (ATBS) for Aishwarya conditions. Laboratory tests represented 200 – 400 days travelling time at the Aishwarya reservoir temperature. The test results indicated on significantly better viscosity retention and higher polymer thermal stability, represented by the polymer cloud point, of ATBS co-polymers than HPAM for Aishwariya field conditions as more suitable polymer type for polymer flooding than HPAM.