Planning EOR Projects in Offshore Oil Fields

Abstract

Abstract Enhanced Oil Recovery (EOR) technologies can significantly increase recovery from oil reservoirs.Some of these EOR technologies are currently producing substantial incremental oil, primarily in onshore applications; others have not yet made a commercial impact. The application of these methods is more complex in the offshore environment, as space and weight restrictions, as well as the need for high reliability and the challenging economics of such projects, impose constraints not present in onshore applications.All EOR processes are reservoir- and reservoir fluid-specific; thus it is necessary to identify the appropriate EOR technology for use in a reservoir, design the project to achieve the required economic incremental recovery within the constraints imposed by the offshore environment, and manage the project to meet or exceed expectations. This paper will focus on the impact of the offshore environment on the planning, design and management of an EOR project. Introduction Oil fields in the offshore environment, especially in the deepwater, represent a significant resource available to meet the expected increases in oil demand over the next few decades. Given the high cost of development, and the resulting necessity for a large reserve base, the size of developed offshore fields is significantly larger than those onshore.Consequently, the remaining resource after primary depeletion (and pressure maintenance/waterflood) in a given reservoir is also larger than the equivalent targets onshore.However, given the constraints in the offshore, both subsurface (very large well spacing, less detailed information about reservoir geology, especially degree of continuity between wells) and surface (availability and cost of EOR agents, weight and space constraints, and high capital cost requirements), the implementation of enhanced oil recovery to increase the recovery efficiency in offshore fields can be fraught with technical difficulties, as well as with economic and technical risks. An appropriate design process1 which takes into account the integrated surface and subsurface can address and mitigate these risks, and can identify whether EOR is appropriate or possible in a given offshore field. Subsurface Information A good understanding of the reservoir geology is critical to the success of an EOR project. Because it is vital to contact remaining oil-in-place with the injectant, the geological understanding should be in sufficient detail to allow modeling of these complicated processes.In most cases, the reservoir will have sufficient production performance so that a history match can be obtained.This will not necessarily provide a sufficient geological description for EOR purposes.In EOR, movement of injectant through a thief zone, causing premature breakthrough, or loss of injectant out of zone, may result in failure of the project.Mineralogy of the reservoir, by determining the amount of adsorption of injectant (in the case of polymer and chemical methods), will dictate the amount of injectant necessary for success. A detailed geologic study should precede any EOR effort.This study should at a minimum revisit all logs, core and fluid data, as well as result in a detailed geologic model that provides a satisfactory history match to production performance. In addition, reservoir fluid and core samples should be obtained and analyzed, and the data specific to the EOR method to be used for project design identified and gathered.It must be remembered that the injected medium will be interacting with both the reservoir fluids and the reservoir rock.These interactions should be well understood.If a pilot is intended, data should be gathered in the pilot area, and detailed geologic modeling carried out specific to the pilot.