Systematic Modelling and Laboratory Testing to Allow the Potential for Economic Inorganic Scale Control in the Brazilian Pre-Salt Fields

Abstract

Abstract Pre-salt oil fields such as those produced in the Offshore market in Brazil, offer a unique set of challenges related to the control of inorganic scale deposits. Scale deposition has the potential to negatively impact production rates and profitability of the operations. Often laboratory testing studies examine the performance of scale inhibitors using so called industry standard techniques like the Dynamic Scale Loop (DSL) but can sometimes be conducted under unrealistic scaling conditions considered by the operators or laboratory scientist to be "worst case". This however can severely limit the number of products that can be successfully qualified for application in the field and lead to recommendations of very high dose rates, which may not be achievable as water cuts increase. To successfully test chemicals in the laboratory prior to field application, the conditions of the tests must closely represent the field. This includes the brine chemistry of the well, the CO2 concentration and pH of the fluids. This paper will detail the results of a new modelling and laboratory study which shows an extremely severe scaling regime that could be expected under the pre-assigned worst case field conditions leading to the failure of chemicals to economically prevent scale. However, when all parameters are considered, laboratory conditions were optimized to represent field conditions more closely, resulting in a more representative (milder) in-situ scaling regime such that chemical performance was significantly improved. Ultimately when the laboratory conditions were tuned to the newly modelled in-situ field conditions, there was a significant reduction in the minimum effective dose (MED) determined in the lab for all conditions, offering the potential for effective treatments to be achieved even at increased water cuts. This work shows that only focusing on one system parameter like maximum field pH results in an overly severe testing regime, limiting the number of products available to the Operating Company. The "worst case" approach also results in the dose rates of those chemicals which are selected being unrealistically high for field application at high water cuts. When more representative in-situ conditions are modelled and then utilised in the laboratory, a wide range of scale inhibitor chemistries would potentially be available for field applications allowing the operator to realize significant OPEX savings. The paper also highlights how careful modelling and optimisation of test conditions is a critical aspect associated with scale inhibitor qualification and highlights the best practice approach to selecting and optimising test conditions in the laboratory to ensure they remain representative of the field conditions.