A sizable number of heavy oil reservoirs that are developed by SAGD in Xinjiang Oilfield in China are heterogeneous and shaly. Particularly the distribution of shale barriers between the horizontal segments of injector and producer has significant impact on the steam chamber development. Conventional steam circulation approach does not consider the location of shale barriers, where poor or no steam chamber develops after converting to SAGD production mode consequently. In order to achieve uniform heat communication, the practical methods of operation during SAGD circulation phase are presented, and the application performances in Fengcheng SAGD project are also discussed.
In this work, the steam circulation is divided into 3 phases: (1)Low pressure circulation phase(Pinj=Pr+0.2MPa); (2)High pressure circulation phase(Pinj=Pfrac-0.5MPa); (3)Partial-SAGD phase, which include 3 cases: case1 where the shale barriers or low permeability sections are located around heel, only the short tubing of injector injects, while the producer continues circulation by long tubing injection and short tubing production; case2 where the shale barriers are located around toe, only the long tubing of injector injects, while the producer continue circulation by long tubing injection and short tubing production; case 3 where the shale barriers are located around the middle of the horizontal segment, the long tubing and short tubing of injector inject simultaneously, while the producer continue circulation by long tubing injection and short tubing production. Other parameters of injection and production are also optimized.
The phase-by-phase steam circulation strategy is particularly effective for SAGD projects with low permeability sections and shale barriers distribution between the horizontal segments. During 2013-2014, 18 wellpairs in Fengcheng SAGD project have been carried out the strategies from this paper and converted into SAGD production phase. Uniform conformance along horizontal sections of the wellpair was achieved, and the oil production rate is 1.5-2 times higher than wellpairs using conventional circulation approaches.