Insights into Permeability Variance in Tight Outcrop Chalk Core Observed During High Temperature Formation Damage Coreflood Testing of a Squeezable Sulfide Scale Inhibitor

Abstract

Matrix permeability impact is a key parameter when assessing the suitability of a squeeze scale inhibitor for field application, and this was particularly true for a new polymeric sulfide scale inhibitor chemistry re-engineered for squeeze treating hot, tight, sour gas condensate chalk producer wells for FeS scale mitigation. The new inhibitor molecule physical size and retention/release behavior, combined with the chalk matrix low permeability and loading capacity, provided some initial question marks with respect to both treatment formation damage potential and also squeeze lifetime longevity. Three years and multiple formation damage corefloods later, and the key questions have now largely been answered. The sulfide scale inhibitor has repeatedly shown minimal formation damage impact when deployed in simulated gas condensate well squeezes in low/very low permeability sandstone and carbonate substrates, and in addition, flowback residual scale inhibitor (RSI) returns data has indicated that significant and indeed extended scale squeeze lifetimes are possible. The following technical account details the final validation coreflood performed in the development series, where successful conclusion would allow the inhibitor to progress to field trial. The ‘proof of concept’ (POC) coreflood required that; (1) the ‘bulk manufactured’ inhibitor (synthesized for field trial) show minimal formation damage impact on field analogous tight chalk core when deployed under target well simulated downhole conditions, and (2) provide the same FeS inhibitory performance and flowback residual scale inhibitor (RSI) profile as generated from the multitude of preceding coreflood series. Besides generating comparative critical gas and condensate core permeability data for fluid transmissibility assessment, the core plug used in the POC flood was subject to tomographic analysis for additional structural/integrity assay. An extensive residual scale inhibitor flowback sampling program was performed to generate inhibitor return data for subsequent use in field-trial squeeze treatment design. The POC coreflood was completed successfully and without incident, and demonstrated minimal formation damage to the chalk core. The flowback RSI profile for the new sulfide scale inhibitor indicated that significant and even extended squeeze lifetime was likely for treatments performed in hot, gas condensate, low permeability chalk well horizons.