Calcite Scale Mitigation in a Very Low Watercut, Low Salinity, HPHT Environment: Lessons Learned in Surveillance, Mitigation and Scale Inhibitor Performance Monitoring for an Onshore Field

Abstract

This prolific field has enjoyed mineral scale free production for many years but has lately experienced a series of unexpected (and harsh!) calcium carbonate scaling events. Well watercuts are barely measurable yet mineral scale deposits accumulate rapidly within wellhead chokes and flowlines. This paper describes the scaling experience and the challenges of mitigation in an extraordinarily low water cut environment. A detailed analysis of the scaling experience is presented: plant layout, scaling locations, scale surveillance and monitoring programs, laboratory testing, product selection and implementation, and scale inhibitor efficacy surveillance and monitoring programs (and details will be provided on each of these topics). The surveillance and application techniques for scale inhibitor deserve mention as very important lessons were learned for low water cut scenarios. For instance, a heavily diluted scale inhibitor was necessary to be effective and the detailed laboratory and field implementation process is described that led to this key lesson learned. Laboratory testing for chemical selection was performed using classical techniques and identified a polymeric scale inhibitor suitable for the scaling scenario. This is reported in detail, however what could not be tested easily in the laboratory was the effect of <1% water cut and how the product would perform in that environment. A risk managed field surveillance program was initiated to determine field efficiency of the polymer, and involved trialing the chemical on a single well pad using temporary installation of a restricted orifice plate (ROP) to help modify the scale inhibitor residence time (and impact of product dilution) for dispersibility and optimum inhibitor action. The lessons learned from this trial were subsequently rolled-out field wide with very positive results. This paper demonstrates a unique scale formation and control situation that utilized a previously unreported and analytical surveillance approach. The cumulative performance derived by improving not only chemical selection, but the way the wells were managed via surveillance and chemical management decision making processes is compelling and of value to other production chemists working in the scaling arena.