First CO2-Enhanced-Oil-Recovery Demonstration Project in Saudi Arabia

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 181729, “Design and Implementation of the First CO2-Enhanced-Oil-Recovery Demonstration Project in Saudi Arabia,” by Sunil Kokal, SPE, Modiu Sanni, SPE, and Almohannad Alhashboul, SPE, Saudi Aramco, prepared for the 2016 SPE Annual Technical Conference and Exhibition, Dubai, 26–28 September. The paper has not been peer reviewed. An operator has designed a demonstration project for carbon dioxide (CO2) enhanced oil recovery (EOR) and has implemented it in one of its fields. The main objectives of the demonstration project are estimation of sequestered CO2, determination of incremental oil recovery, and evaluating the risks and uncertainties involved, including migration of CO2 within the reservoir and operational concerns. It is estimated that approximately 40% of the injected CO2 will be sequestered permanently in the reservoir. Project Design Conceptual Road Map and Screening Studies. Given the relatively light nature of crude oils and generally high reservoir pressures in Saudi Arabia, CO2 injection is a viable recovery method, especially in flooded reservoirs. An initial screening highlighted several good candidates for CO2 injection. A mature, waterflooded part of a large oil field with a carbonate reservoir was selected as a candidate for CO2 injection. Further studies were conducted for the candidate reservoir that included laboratory, feasibility, and detailed reservoir-simulation studies. This reservoir has been flooded for decades in a peripheral water-injection mode, and considerable reservoir and production data were available. Laboratory Studies. Two sets of experimental studies must be conducted for any given CO2-EOR prospect: fluid/fluid and fluid/rock interactions. The important laboratory experiments include the minimum miscibility pressure of the crude with CO2, swelling and fluid properties of CO2/oil mixtures, asphaltene precipitation onset and bulk asphaltene deposition, and oil-recovery potential by use of coreflooding studies. It must be emphasized that these experiments need to be conducted at reservoir conditions with live reservoir fluids and supercritical CO2; otherwise, the data have limited value at best. Simulation Studies. The reservoir selected for CO2 injection is a Jurassic carbonate reservoir, and the area selected is in a downflank, flooded part of the field. The selected area has been on peripheral water injection for more than 50 years and has been well-waterflooded because of its proximity to the peripheral injectors. Approximately 40 MMscf/D of relatively pure CO2 was available from a gas plant approximately 85 km from the pilot site. The slimtube data show that the minimum miscibility pressure is lower than the reservoir pressure, indicating that the CO2 will develop a miscible displacement in the reservoir at current reservoir pressures. The main objectives of the simulation study were as follows: Carry out screening and mechanistic studies and find areas suitable for a CO2-injection pilot. Assess the amount of CO2 sequestered over the period of the pilot testing. Assess incremental oil recoveries associated with different modes of CO2 injection. Optimize the pilot design within the reservoir and operational constraints.