Study on Surfactants for Replenish Energy before Fracturing in Tight Reservoir

Abstract

Tight reservoir in the periphery of Daqing oilfield is abundant. However, due to tight lithology, poor physical properties, and insufficient formation energy, water injection is not effective, development effect is not ideal, and utilization degree is low. Therefore, it is proposed to implement energy replenishment before fracturing, integral fracturing, and energy storage after fracturing. In the energy replenishment stage, surfactants with good compatibility with the formation and strong oil washing ability are selected as injection medium to play the dual role of energy replenishment and oil washing, and improve the recovery rate of tight sandstone reservoirs. Surfactants are evaluated by established method; LH anionic surfactant and KR anionic non-ionic surfactant are preferred. Under alkali free condition, interfacial tension of two surfactants maintain at order of 10-3. Recovery degree of surfactants in natural cores reach more than 15%. Field application conducted in 30 wells in Block P, including 27 vertical wells and 3 horizontal wells. Oil is seen in vertical wells at 7.8% flow back rate. The average daily liquid production of the 20 wells that have been pumped is 7.5 tons per day, with a daily oil production of 1.3 tons, and a cumulative oil increase of 223.8 tons per well. The average daily oil increase of a single well in the three months after fracturing a qualified oil well is 5.2 tons, 1.6 times and 2.2 times that of dessert fracturing and overall fracturing in the same period. The average daily liquid production of 3 horizontal wells is 24.2 tons, and the daily oil production is 9.6 tons. The test results show that the overall design of the fracturing energy supplement scheme is reasonable, and the selected surfactant can supplement the formation energy while improving the oil washing efficiency, which will provide technical support for exploring new ways to improve oil recovery in tight reservoirs.