Chemical Enhanced Oil Recovery (EOR) has seen numerous applications worldwide onshore but very few offshore. The reasons for that are mostly related to the technical and logistical challenges that need to be overcome for the successful implementation of chemical EOR: transporting various chemicals to the platforms, the need for space for the mixing skids and storing chemicals on the platforms, the need to use sea water as the injection fluid among others. As primary and secondary recovery reach their technical and economical limits in offshore fields, the operators are faced with the dilemma of abandoning the field and the platforms or resorting to EOR to increase recovery and extend the life of the field. Non chemical EOR techniques face their own challenges such as the need for large gas supply for gas injection so chemical methods cannot be ruled out so easily. However new approaches need to be defined to make chemical EOR a realistic method for offshore reservoirs. A large part of these issues arise from the mindset which associates chemical EOR with Alkali-Surfactant-Polymer injection. The approach proposed is to use only surfactant in cases where polymer is not absolutely required and to eliminate alkali altogether. This will eliminate various obstacles such as deck space limitations and the need to soften the injection water. This approach opens new doors for chemical Enhanced Recovery offshore. Such an approach is possible thanks to the progress in surfactant formulation and the development of adsorption inhibitors which allow dealing with seawater as an injection fluid. The novelty is not the technology but the way the standard approach is discarded to the benefit of a simpler solution.
Oil production in presence of a bottom aquifer is one of the most challenging issues in reservoir engineering. In most cases water coning happens very quickly and the influx of water restricts oil production and limits recovery. The problem is even more difficult when the oil is heavy because the viscosity contrast is large. In some cases horizontal wells may be used to improve the situation but when reservoirs are thin and the oil is viscous even horizontal wells are of limited use. This paper presents the challenges and potential solutions for Enhanced Oil Recovery in heavy oil reservoirs with bottom aquifer.
Existing literature is reviewed for field cases of EOR experience with bottom aquifer for chemical as well as thermal processes (SAGD, steam injection as well as In Situ Combustion).
In the case of chemical EOR the chemicals may be lost to the aquifer; for thermal recovery the bottom water can act as a heat sink and affect and steam oil ratio. Some in-situ combustion projects have been successful in such settings but in every case the outcome is the same: the economics of the project can be affected.
The paper contains some previously unpublished data of polymer injection in a heavy oil pool with some limited bottom aquifer; for the most part it is a review of the existing literature which may prove useful to practicing engineers who are faced with the issue of developing heavy oil resources in the presence of bottom aquifer.
Taken from: Journal of Petroleum Technology – January 2015
Authors: Eric Delamaide (IFP Technologies (Canada) Inc.) \ Alain Zaitoun (Poweltec) \Gerard Renard (IFP Energies nouvelles) \ Rene Tabary (IFP Energies nouvelles)
The Pelican Lake heavy oil field located in northern Alberta (Canada) has had a remarkable history since its discovery in the early 1970s. Initial production using vertical wells was poor because of the thin (less than 5m) reservoir formation and high oil viscosity (600 to over 40,000cp). The field began to reach its full potential with the introduction of horizontal drilling and was one of the first fields worldwide to be developed with horizontal wells. Still, with primary recovery less than 10% and several billion barrels of oil in place, the prize for EOR is large.
Initially, polymer flooding had not been considered as a viable EOR technology for Pelican Lake due to the high viscosity of the oil, until the idea came of combining it with horizontal wells. A first – unsuccessful – pilot was implemented in 1997 but the lessons drawn from that failure were learnt and a second pilot met with success in 2006. The response to polymer injection in this pilot was excellent, oil rate climbing from 43bopd to over 700bopd and remaining high for over 6 years now; the water-cut has generally remained below 60%.
This paper presents the history of the field then focuses on the polymer flooding aspects. It describes the preparation and results of the two polymer flood pilots as well as the extension of the flood to the rest of the field (currently in progress).
Polymer flooding has generally been applied in light or medium gravity oil and even today, standard industry screening criteria limit its use to viscosities up to 150cp only. Pelican Lake is the first successful application of polymer flooding in much higher viscosity oil (1,000-2,500cp) and as such, it opens a new avenue for the development of heavy oil resources that are not accessible to thermal methods.