The main objective of this paper is show the design, implementation and results of a nitrogen + steam pilot implemented in a Colombian heavy oil reservoir. Given that the answer to the cyclic steam injection has declined significantly in some wells of the interest field due to the high number of cycles, a pilot project to assess the feasibility of injecting nitrogen accompanied cyclic steam was raised. The determination of optimum volumes and injection scheme by numerical simulation was performed in a sector model. Eleven schemes of steam plus nitrogen injection were evaluated. In all schemes, it was tested remained constant volume of injected steam, while the volume of nitrogen varied according to the scheme (pre-injection, post-injection, co-injection or a combination of the above). In all cases, it assumed the injection of nitrogen according to real drive capacity 1200 m3/hour (1017072 ft3/day). The best case corresponds to start injecting only one day with nitrogen, followed by five days of co-injection and ending with a single nitrogen day. Under this scheme an incremental production of 5642 barrels of oil a trial period of six months, with average oil production of 53 BOPD in the same period and maximum rate of 142 BOPD. According to the simulation results, it was decided to implement the pilot steam + nitrogen injection, following the best injection scheme given above; that is, a day of pre-injection (nitrogen only), five days of co-injection (steam + nitrogen) and one day post-injection (nitrogen only). The results of the pilot show that oil production has increased compared to previous cycles, reaching similar results to the numerical simulation forecast. A methodology to implement steam injection enhanced with nitrogen is proposal in this paper, which can be applied in any field of heavy crude scheme developed under cyclic steam stimulation.

This paper shows the evolution of the cyclic steam stimulation (CSS) process in a Colombian heavy oil field. Some challenges have been faced like: low injectivity in the first stimulation cycles, presence of swelling clays, low lateral and vertical continuity of the producing sands, steam channeling, among others. According to the oilfield complexity some strategies are currently being implemented after previous studies of numerical simulation and lab test evaluation: diesel slug to improve injectivity, reduced steam quality in the first cycles to increase steam injectivity, using clay inhibitor during steam injection, reduced spacing in the better zones according to opportunity index map, nitrogen injection in wells with more than six stimulation cycles, high frequency cycles and changes in completion design and drilling scheme among others. The set of lab test, numerical simulation and pilot test have resulted in the following: 1) Use of diesel slug before steam soaking clean the hole improving injectivity, allowing more steam volume injection. 2) Reduce steam quality in first stimulation cycles is useful to increase injectivity without significantly affecting steam oil ratio SOR. 3) Using an index map opportunity help to easily identify areas with the greatest potential for infill wells. 4) Injecting nitrogen with steam in wells with more than six stimulation cycles improve production results due to the pressurization of producing sands. Key recommendations for implementing a CSS process in heavy oil reservoirs with low lateral and vertical continuity of the producing sands, swelling clays and low net to gross are presented in this article. The recommendations range from the first injection cycles to maturity of the process and the search for new production alternatives.

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