Abstract
A pilot test of alkali/polymer (AP) combination flooding was conducted in the west area of the fault block of XingLongTai oil field, which was a fringe water reservoir with a gas-cap. There are 11 wells in the oil-bearing area which is 2.05 km2. The central well group contains 3 injection wells and 1 production well and has an oil-bearing area of 0.037 km2. The injection of a slug of 0.35PV of AP combination solution (2% NaCO3 + 1000 mg/L Polymer (1175A)) was initiated in January 1995 when the oil recovery was 46.75% (OOIP) and the water cut was 96.1% and finished in February 1997 when subsequent water injection was started. Up to August 1998, the average water cut was decreased from 98.0% (prior to AP injection) to 93.5% and the oil recovery was increased by 1.98% (OOIP) for the whole pilot area. The water cut was decreased from 98.0% (prior to AP injection) to 85.6% and the oil recovery was increased by 18.5% for the central well group. Numerical simulation was performed and forecasted using the modified UTCHEM (University of Texas Chemical Flood Simulator). The calculation has shown that AP combination flooding can give a much higher oil recovery than water flooding. The ultimate oil recovery by AP combination flooding for the whole pilot area is 50.1% and 147 tons oil can be produced with one ton polymer. Because the pilot area is of a small scale and the initial invest is larger, the economic benefit is not good enough, but the AP combination flooding does be an effective way to enhance oil recovery after water flooding. It is especially true if the target field is of a larger scale. The influence of alkaline loss on EOR, the effect of AP combination system on sweep efficiency and the causes of formation damage are also studied in this paper.
