Reinforced expansion of dual-horizontal-well SAGD steam chamber: An intermittent huff-and-puff approach

In highly heterogeneous ultra-heavy oil reservoirs, the dual-horizontal-well SAGD commonly suffers from interference between injection and production wells, uniform production profile of the horizontal wellbore and a small steam chamber with slow expansion, which leads to long-term low production and low efficiency of SAGD well groups. To improve the recovery performance, this research proposed a reinforced SAGD steam chamber expansion technology for dual horizontal wells, based on the intermittent huff-and-puff operation. A case study of numerical simulation was performed for the M block of the Xinjiang Fengcheng oilfield to systematically investigate key parameters, such as the huff-and-puff operation scheme, injection-production parameters and operation switch timing. The results showed that with proper injection-production parameters, the recovery performance can be effectively improved by the intermittent huff-and-puff, in which the steam is injected into the steam injection well (with the production well being shut in) and the production well starts to produce (with the injection well being shut in) after some time of steam soaking; the resultant recovery factor reaches 53.8%. The mechanisms of this technology are as follows: (1) high-rate injection of steam during the huff operation reduces the heat loss of steam; (2) the effects of steam channeling and formation pressure difference are eliminated for steam injection, which helps steam to sweep the insufficiently-recovered zone; and (3) gravity drainage continuous to work during steam injection and the resultant liquid level in the production well can effectively prevent steam channeling during production and facilitate high-efficiency oil drainage. The field testing of this well has been performed in two well groups of the M block, the Fengcheng oilfield. The resultant production is stable, with an increment of daily oil production of 1.5 t/d. The research results provide references for improving the recovery performance of analogous oil reservoirs.