A comprehensive review on Enhanced Oil Recovery by Water Alternating Gas (WAG) injection

Recent Developments and Updated Screening Criteria of Enhanced Oil Recovery Techniques

Interactions between organic acids anions in formation waters and reservoir mineral phases

The rate of replacement of produced oil and gas reserves by new discoveries is in a state of steady decline. Instead of searching for rare new oil fields, it is more economically justified to improve production from the existing and known fields. This is often achieved using enhanced oil recovery (EOR) technologies. The application of EOR in the North Sea dates to the mid-1970’s with most of the fields being flooded with gas due to their light oils. Following a critical review of relevant published literature, the EOR methods in the past five decades are: water alternating gas (WAG), miscible gas injection (MGI), foam assisted water alternating gas (FAWAG), simultaneous water and gas (SWAG), and microbial enhanced oil recovery. The first part of this paper explores the advantages and limitations of the field implementation of gas EOR methods in North Sea oil fields. In the second part, new screening criteria of WAG, SWAG, MGI and FAWAG were developed by performing statistical analysis of the data from the past field experiences, especially in the North Sea. The screening criteria of the future methods are clearly documented in the literature and therefore not covered in this study. From the screening criteria, it has been identified that most North Sea fields qualify for WAG. This explains why WAG has been the most common scheme in the North Sea. FAWAG should also be implemented either after WAG or SWAG when the residual oil saturation is < 20%.

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A review of gas enhanced oil recovery schemes used in the North Sea

Multiphase flow characteristics and EOR mechanism of immiscible CO2 water-alternating-gas injection after continuous CO2 injection: A micro-scale visual investigation

Screening of WAG Injection Strategies for Heterogeneous Reservoirs

This paper reviews reservoir performance and management of the Statfjord field after 8 years of production. The reasons behind the reservoir development strategies and field experiences are presented. The field comprises three reservoirs produced simultaneously with designated wells for each reservoir: the Upper and Lower Brent and the Statfjord. The two Brent reservoirs are produced with a waterflood, while the Statfjord reservoir is produced with a high-pressure miscible gasflood. The original development plans have been refined on the basis of field performance through an extensive monitoring program and use of reservoir simulation. The induced gamma ray spectra (IGRS) log is used to monitor water movement in the Brent reservoirs, while the compensated neutron tool (CNT) is the main tool used to monitor the gasflood in the Statfjord reservoir. The acquired data have improved the geologic model and the knowledge of fluid movements in all three reservoirs. This resulted in a large and complex reservoir simulation model with more than 20,000 gridblocks.

Sigurd A. Haugen

Papers

Screening of WAG Injection Strategies for Heterogeneous Reservoirs

Statfjord field: development strategy and reservoir management