Surfactant Flood in a Tight Carbonate Reservoir in North Oman

Abstract Daleel has undertaken an extensive endeavor to establish the technical viability of chemical enhanced oil recovery (EOR) method in the Shuaiba carbonate reservoir, which aims to demonstrate the feasibility of surfactant injection through detailed lab work followed by field applications. The Upper Shuaiba carbonate formation presents challenging conditions, characterized by high formation water salinity (~180,000 ppm), tight matrix (permeability of 1-15md) with fractures, and reservoir temperature of ~85°C. In light of the continuous gradual increase of the water production from the field and expected ultimate recovery factor from the ongoing water flood, an extensive work program has been conducted since 2010 to identify the most suitable and effective EOR technique for the Shuaiba carbonate reservoirs. This process began with lab tests to analyze fluid behavior and core flooding experiments for the selected surfactant. Subsequently, field trials were conducted including huff-and-puff test in a vertical well and then continuous injection in two horizontal water injectors for three months. Detailed results from both lab experiments and the first field trials were documented in a prior paper (Al-Sinani et al., 2016). This paper discusses the result of the field trial conducted in March 2018, which yielded 40 kbbl of oil gain and a 5-10% reduction in water cut during two years. The field trial took place in a mature water flood pattern with 100-meter well spacing, involving a horizontal water injector and two adjacent oil producers. Over three months, surfactant was successfully injected at a concentration of 1.3%. A robust monitoring plan, including well-testing, surface wellhead sampling, and time-lapse production logging, was carried out during and after the chemical injection. The field trial result, along with the previous reported initial lab and field data, paved the way for the expansion of surfactant EOR into a full block including 15 water injectors and 35 oil producers. The full-block surfactant flood was planned in two phases from 2023 to 2026. Phase I surfactant injection took place in a small sector with 3 injectors and 5 producers from Jan to Apr in 2023 to validate oil gain based on the dynamic model results, re-evaluate project economics, and assess any surface and subsurface potential risks for Phase II. In this paper, an overview of the Phase I execution including challenges will be highlighted. Obvious water cut reduction was seen within 3 months after the surfactant injection, and then the water cut went back to the historical level. A clear oil gain above water-flood base line has been observed from the pattern of Phase I within 15 months but was assessed as below initial forecast. This paper will discuss the possible reason for the lower than the expected oil gain and the future plan of the surfactant flooding in Daleel fields.