Study on Surfactants for Replenish Energy Before Fracturing in Tight Reservoir

Tight reservoir in Daqing periphery oilfield is abundant. However, due to low-permeability, poor physical properties, and insufficient formation energy, water injection is not effective, development effect is not ideal, and producing 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 are selected as injection medium to replenish energy and improve displacement efficiency. 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 in natural cores is 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 20 wells that have been pumped is 7.5 t per day, with a daily oil production of 1.3 t, and a cumulative oil increase of 223.8 t per well. The average daily oil increase of a single well in three months after fracturing is 5.2 t, 1.6 times and 2.2 times that of dessert fracturing and overall fracturing in same period. The average daily liquid production of 3 horizontal wells is 24.2 t, and the daily oil production is 9.6 t. The results show that overall design of the fracturing energy supplement scheme is reasonable, and the selected surfactant can supplement formation energy while improving displacement efficiency. This will provide technical support for developing tight reservoirs.