Dreaming Big “Surfactant Injection in a Giant Offshore Carbonate Field”, From Successful Injection Trials to Pilot Design and Implementation

Abstract

Summary Al-Shaheen Field, offshore Qatar, is responsible for 45% of Qatar s crude oil production. Kharaib,the most prolific reservoir of Al-Shaheen Field, is an oil wet tight carbonate. Even after an extensive water-flooding for several years, there is substantial amounts of oil left behind owing to the highly oil-wet nature of the reservoir. Wettability altering surfactant offers a very promising EOR technique with ability of releasing the residual oil from tight oil wet pores. Three successful short surfactant injection trials have led to comprehensive planning for conducting a long term surfactant injection pilot to evaluate incremental oil gain. The pilot planning consists of three-tier approach; additional laboratory experiments, reservoir modelling and field implementation. Laboratory experiments were performed to establish surfactant formulation s stability and adsorption in presence of reservoir fluids and rock. Core floods were performed to estimate incremental recovery with different surfactant slug sizes and concentration. Core flooding results were history matched to obtain necessary parameters for field scale modelling. The candidate location was selected considering reservoir properties, operational constraints and implementation feasibility. The unique ability of this surfactant is to alter reservoir surface wettability with low adsorption on the rock surface and negligible change in interfacial tension. Core flood experiments showed significant oil recovery and field trials showed injectivity improvements which were indication of the wettability alteration to more water wet state. A long term pilot is planned to establish the surfactant EOR potential in Al-Shaheen reservoirs. Several evaluation options for the success of this pilot such as single well tracer test, inter-well tracer test, micro-pilot tests, time lapse saturation logging, and observation wells have been assessed. Reservoir modelling, logistical considerations, field applicability, drilling schedule and cost implications have been considered for determining the most optimum solution to help de-risk field scale implementation. This paper presents a phased approach to scale up an EOR project in a highly complex offshore carbonate field. A novel EOR implementation approach called S3IP (Surfactant Induced Improvement in Injectivity and Productivity) is applied which results in incremental recovery and injectivity improvement with single EOR agent. The phased approach taken, from screening the surfactants to short term injectivity trials and then continuing to a long term pilot, is unique for the offshore field and the current oil price condition. This pilot will demonstrate the ability to deliver and inject large quantity of surfactant in challenging offshore environment and to exhibit incremental recovery potential of field scale implementation.