After two decades of relative calm, chemical EOR technologies are currently revitalized globally. Techniques such as alkaline surfactant-polymer flooding, originally developed by Shell, have the potential to recover significant fractions of remaining oil at a CO2 footprint that is low compared to, for example, thermal enhanced oil recovery, and they do not depend on a valuable miscible agent such as hydrocarbon gas. On the other hand, chemical EOR technologies typically require large quantities of chemical products such as surfactants and polymers, which must be transported to, and handled safely in, the field. Despite rising industry interest in chemical EOR, until today only polymer flooding has been applied on a significant scale whereas applications of surfactant-polymer (SP) or alkaline surfactant-polymer (ASP) flooding were limited to multi-well pilots or to small field scale. Next to the oil price fluctuations of the past two decades, technical reasons that discouraged the application of chemical EOR are excessive formation of carbonate or silica scale and of strong emulsions in the production facilities. Having identified significant target oil volumes for ASP flooding, Petroleum Development Oman (PDO), supported by Shell Technology Oman, carried out a sequence of single-well pilots in three fields, sandstone and carbonate, to assess the flooding potential of tailor-made chemical formulations under real subsurface conditions, and to quantify the benefits of full- field ASP developments. The paper discusses the extensive design process that was followed. Starting from a description of the optimisation of chemical phase behaviour in test tubes as well as core-flood experiments, we elaborate how the key chemical and flow properties of an ASP flood are captured to calibrate a comprehensive reservoir simulation model. Using this model we evaluate PDO's single-well pilots and demonstrate how these results are used to design a pattern-flood pilot.

No abstract

In a number of fields in Oman thermal developments are being implemented. One of these fields is located in South Oman and contains an exceptional 200 m thick oil thick column of medium to heavy oil (200 to 800 cp). This sandstone reservoir is at a depth of 1050 m below surface and is underlain by a modestly strong aquifer. The field has been in production for 20 years, the main production mechanisms are pressure depletion and natural ingress of aquifer water. For the next phase of development a vertical pattern steam flood re-development is planned which will increase the ultimate recovery significantly. The extreme thickness of the heavy oil reservoir is unique for steam floods and poses both opportunities as challenges. There are no direct analogues and the normal practices of managing a steam flood need to be verified and adjusted. For that reason a range of numerical tools has been developed.The tool box consists of: 1) An explicit well bore model to understand e.g. the internal well fluid dynamics and heat exchange between tubing, annulus liquids and reservoir fluids at the reservoir level as well as the overburden. Particular interesting is the impact of cool aquifer water inflow on condensation of steam in the annulus and near well bore area. 2) Radial models for detailed analysis of recently performed steam soaks. 3) Sector models (1/12 pattern) for capturing overall steam flood performance and to understand the impact of fine scale reservoir heterogeneity, 4) A single pattern model for analysis of the ongoing steam flood trial in the field and 5) A 10pattern model cut-out of the geological model for understanding of pattern interference and impact of major reservoir features like faulting and structure. The models have been constrained by the long production history of the field. The performance of the tools is illustrated by the work-out of some specific well and reservoir management examples.

In a number of fields in Oman thermal developments are being implemented. One of these fields is located in South Oman and contains an exceptional 200 m thick oil thick column of medium to heavy oil (200 to 800 cp). This sandstone reservoir is at a depth of 1050 m below surface and is underlain by a modestly strong aquifer. The field has been in production for 20 years, the main production mechanisms are pressure depletion and natural ingress of aquifer water. For the next phase of development a vertical pattern steam flood re-development is planned which will increase the ultimate recovery significantly. The extreme thickness of the heavy oil reservoir is unique for steam floods and poses both opportunities as challenges. There are no direct analogues and the normal practices of managing a steam flood need to be verified and adjusted. For that reason a range of numerical tools has been developed.The tool box consists of: 1) An explicit well bore model to understand e.g. the internal well fluid dynamics and heat exchange between tubing, annulus liquids and reservoir fluids at the reservoir level as well as the overburden. Particular interesting is the impact of cool aquifer water inflow on condensation of steam in the annulus and near well bore area. 2) Radial models for detailed analysis of recently performed steam soaks. 3) Sector models (1/12 pattern) for capturing overall steam flood performance and to understand the impact of fine scale reservoir heterogeneity, 4) A single pattern model for analysis of the ongoing steam flood trial in the field and 5) A 10pattern model cut-out of the geological model for understanding of pattern interference and impact of major reservoir features like faulting and structure. The models have been constrained by the long production history of the field. The performance of the tools is illustrated by the work-out of some specific well and reservoir management examples.