An Effective Way to Develop a Thin-layered Heavy Oil Reservoir within Economic Margin
Authors: Ren Fangxiang , Sun Yan , Yu Tianzhong , Fan Hongzhao , Lv Jianyun , Nie Xiangbin , Song Ju , Wang Ruo , Zou Mi , Niu Yuqaing , Bin Yang 
Published: June 2012

More than 50% of the heavy oil resources for PetroChina Liaohe exist in thin (approximately 3- to 8-m thick) reservoirs. For this type of reservoir, steamflooding with conventional vertical wells is not economically profitable, and in-situ combustion methods are not applied because of operational difficulties. Horizontal well technology brought a new direction to attempts to improve technical and economic performance of steamflood operations. Many experiments had been conducted to use the technology in the Liaohe oil field to achieve economic production, but the expected results were still not achieved. Lessons learnt indicate that the root cause is the poor oil contact of the horizontal wells’ trajectories in the thin, heavy oil reservoir. A pilot project was conducted to explore whether horizontal well technology in combination with optimized cyclic steam stimulation could deliver economic production from these thin heavy oil reservoirs. Horizontal well placement was accomplished by using near-bit azimuthal measurements and images.

Both the feasibility and economic performance of the technology have been studied in this five-well pilot project. Comparing the performance of these five wells to the previous ones, the results indicate that 1)The well-placement drilling solution can maximize the oil contact up to an average 91% of net-to-gross coverage.2)The well-placement drilling solution improved drilling efficiency by 40%.3)The drilling operation was conducted with no nonproductive time (NPT), compared to the previous NPT maximum of 6 days.4)The well-placement drilling solution did keep the cost flat, and the cost even slightly declined.5)The optimized cyclic steam stimulation in well-placement-drilled wells can decrease the cyclic steam stimulation cost over production to 1000 RMB/ton, which is recognized as an economic ideal in the industry.6)The daily block production has increased from 20 tons/day to 72 tons/day after using the combined well-placement-drilling and cyclic steam stimulation technology, which is an increase of 210%.7)The income/input ratios at the end of the fourth year for the two better wells are both 1.48 (reaching a balance at the second and third years, respectively), and ratios for all five wells ratios averaged 0.93, which means the wells will earn net money at the beginning of the fifth year. Compared to the ratio of 0.03 for a previously drilled well, this is not only a big financial improvement, but is also an incentive to revitalize many similar thin heavy oil reservoirs because it proves the possibility of developing them within the economic margin.

The success of the pilot project proved to us that horizontal well-placement drilling in combination with optimized cyclic steam stimulation is an effective way to develop thin-layered heavy oil reservoirs within the economic margin in Liaohe oil field. We extended this horizontal well technology to other blocks and have achieved repeated success.