Improved Sweep in Bati Raman Heavy-Oil CO2 Flood: Bullhead Flowing Gel Treatments Plug Natural Fractures

Abstract

Summary This paper covers the successful pilot field application of polymer gels for reservoir conformance improvement in the ongoing CO2 injection project at Bati Raman heavy-oil field in southeastern Turkey. Bati Raman is a naturally fractured carbonate reservoir in which the heterogeneities and the unfavorable mobility ratios between CO2 and the heavy oil cause inefficient sweep of the reservoir. These conditions prompted the pilot application of a conformance-improvement fracture-plugging (flowing) gel system in three wells in July 2002. Based on injection tests performed in the field, approximate treatment volumes were estimated to be on the order of 10,000 bbl for each well. Volumes actually pumped ranged from approximately 6,500 to 11,000 bbl. All three of the wells showed a gradual increase in injection pressure during treatment, indicating a decrease in injectivity index as treatment progressed. During one treatment, an offset producer experienced changes in fluid level consistent with rapid pressure transmission via the connecting fracture early in the treatment, with later loss of such communication. This behavior provides direct evidence of fracture plugging during treatment (Lane 2002). A mechanistic semianalytical model based on previously published laboratory work (Lane and Seright 2000) obtained a good match with the field data. The rate/pressure data were fed into the model, and effective fracture widths were backcalculated. Comparisons of results with the Formation MicroImager (FMI) log findings are explained. Gel-monitor well responses were scaled based on field data using a Fetkovich type decline-curve analysis. These studies enabled the incorporation of the effect of reservoir heterogeneities on the gel propagation radius so that future gel-treatment design parameters could be optimized. Pre and post-treatment CO2 injection pressures and the rates are as shown in Table 1. Sweep efficiency was increased as defined by produced oil/injected gas ratio. The 1-year average post-gel oil rate from 19 offset producers is 720 STB/D, as compared with apre-gel oil rate of 645 STB/D. The rate of increase from the treatments is thus 75 B/D, or 12%, which indicates a payout time of 12 months. Keeping this enlightened approach and seizing on the key concepts, four more CO2 injector wells were treated in 2004 to follow up on the encouraging results.

A Quarter Century of Progress in the Application of CO2 Immiscible EOR Project in Bati Raman Heavy Oil Field in Turkey

“…This provided a favorable but short term response, further confirming that the predominant limitation with the current CO 2 flood is bypassing of the reservoir matrix through the fractures, greatly reducing the sweep efficiency (Senol Topguder 1999; Karaoguz et al 2004).…”

Enhanced Oil Recovery: An Update Review

“…In simple terms, if CO 2 is available it will remain the most sound recovery choice for carbonate reservoirs unless more viable EOR strategies are developed. Canada (e.g., Enchant Midale, Judy Creek, Swan Hills and Weyburn) and Turkey (e.g., Bati Raman) also report well documented CO 2 -EOR projects in carbonate formations [18,[227][228][229][230]. It is important to remark that Weyburn represents a large CO 2 -EOR project based on anthropogenic sources (Coal gasification) of CO 2 .…”

Applied Technologies and Prospects of Conformance Control Treatments in China

“…Typical chemicals are weak gel, Preformed Particle Gel (PPG), Colloid Dispersion Gel (CDG), clay gels, and industry wastes. Polymer concentrations usually range from 800 to 2000 mg/L for weak gel and from 400 to 1000 mg/L for CDG, both of which are also studied and used in the other part of the world [47][48][49][50][51][52]. Specifically, China accumulated quite a lot experiences in the use of PPG, clay gels and industry wastes, such as sludge from produced water treatments, oily sludge from oil production and processing.…”