Development of Heavy Oil Fractured Carbonate Bati Raman Field: Evaluation of Steam Injection Potential and Improving Ongoing CO2 Injection

Abstract

With 1.85 MMM bbl OOIP, the Bati Raman field is the largest oil field in Turkey. After its discovery in 1961, the field was put on stream for primary production until 1986. The recovery factor was only 2% after twenty five year production mainly due to low oil gravity. The well-known immiscible CO2 flooding project commenced in 1986, and the recovery factor reached 5% at the end of 2007. The recent steady decline in production entails the implementation of new development plans and this paper summarizes these efforts. After reviewing the performance of the current CO2 injection, short and long term development strategies were discussed. Short term plans include the continuation of the CO2 project in the areas where it is still viable. Some parts of the field are under WAG process. To improve the recovery in the short run by a better sweep (or displacement), a chemically augmented water injection process was proposed in those areas. Potential chemicals (surfactants and alkalis) were tested for wettability alteration and IFT reduction applying static (spontaneous) imbibition experiments. The best performing chemicals were determined for the field pilot after an economic analysis. In addition, the possibility of steam injection into the field was evaluated for the long run. Due to extreme heterogeneity and fractured structure, crestal steam injection that uses steam as heating rather than a displacement agent was proposed. An analytical study for the optimization of steam injection was provided. To determine the locations for the above listed processes, an extensive reservoir characterization study was performed using dynamic and very limited static -well- data. Using well recorded primary (1961–1986) and CO2 production data (1986–2007), fracture swarms were mapped. In this process, the changes in the initial production rate and GOR over different time periods were considered. The quickest decline in the initial rate and the lowest GOR areas correspond to highly fractured regions. Highly -vertically- fractured areas (typically the crest) were determined for potential steam injection. This analysis also helped detect high quality matrix areas as candidates for chemically augmented WAG.

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

“…In fact, as seen in Fig. 6, all surfactant cases followed a similar trend of recovery, but NaOH revealed less preliminary recovery and then a razor-sharp increase, which could be an evidence of wettability change eventually yielding a higher capillary imbibitions recovery than any other surfactants (Babadagli et al 2008(Babadagli et al , 2009.…”

“…But concentration of additive was slightly increased taking into account the effect of chemical retention and the field pilot was started in 2010. Recognizing through the lab tests that the wettability alteration by NaOH is not an immediate process, the field response is projected to be relatively slow (Babadagli et al 2008(Babadagli et al , 2009). The pH, liquid level and production data were recorded frequently at the neighboring wells.…”

“…At this stage, steam injection is an inevitable alternative for field wide development of the Bati Raman field since thermal diffusion is nearly five times faster than mass diffusion and this makes thermal applications much more favorable in terms of matrix oil recovery from heavy-oil fractured carbonates (Babadagli et al 2008(Babadagli et al , 2009. Although, the heterogeneous structure that causes early breakthrough of injected steam and uneven distribution of the heat is the main challenge in steam injection in carbonates, it is still measured as the only viable course of action for heavy-oil recovery even in challenging circumstances.…”

“…5-spot pilot performed in the field in 1969 showed that the displacement type injection in this kind of fractured reservoirs is not feasible. Therefore, it was recommended to use steam as a heating agent rather than a displacement fluid (Babadagli, et al 2008(Babadagli, et al , 2009. Injection of steam into formation from top to heat the reservoir (crestal injection) using vertical communication towards the bottom is an alternative to enhance gravity drainage as suggested earlier (Shahin et al2006;Snell and Close 1999).…”

“…Through an analytical modeling exercise, with 4200 ft. depth 1,000 cold water equivalent (CWE) B/D steam injection was found to be an optimal value yielding a steam quality of 0.4 at the crest of the reservoir. Since the rate is the most critical factor on the heat loss and steam quality, half of the suggested optimal rate (500 CWE B/D) gave only 0.05% steam quality (Babadagli et al 2008(Babadagli et al , 2009. With the improving technology of the vacuum insulated double walled tubular products that reduces heat transfer loss, it is considered that the drawback of depth for steam quality in the Bati Raman field can be minimized (Lombard 2008).…”