Water-Alternating-Weak Gel Technology and its Application in High Water Cut Oil Reservoir in Bohai Oilfield

Abstract

NB oilfield, as the one of typical blocks of the Bohai Oilfield, is a heavy oilfield with an oil viscosity of 413~741mPa·s. Therefore, when injecting water, water channeling of production wells is very serious. As a regular and useful technology to control mobility, weak gel flooding has been used in NB oilfield since 2005, which increased by oil production up to 110,000 cubic meters. However, this technology usually results in inefficient displacement of weak gel in the late injection stage because of growing of high permeability layer. The field test documents show that the suction profile has reversed in 2015 since water entry ratio in low permeability layers decreases from 26.2% to 12.4%. Correspondingly, oil wells have tiny water cut decrease range and product polymer as high as 400 mg/L.To improve the above disadvantage of weak gel flooding in the late development stage, laboratory experiments are carried out firstly to verify water-alternating-weak gel to adjust profile inversion. The experimental results show that the reversal time of profile is delayed from 0.8 PV to 1.35 PV and water entry ratio in low permeability layer increases by 13% ~ 27%, obtaining oil recovery rise by 1.7%~4.6%. It indicates that water-alternating-weak gel technology can adjust and balance resistance in high and low permeability layer by designing different size of weak gel slug. Based on the laboratory experiment, during the period from 2016 to 2017, we conducted field applications in three well groups in NB oilfield. The weak gel was first injected for one month, followed by water injection for one month, which was repeated for a total of 8 times. Compared with the continuous flooding of weak gel, the total agent dosage decreases by 51%, the oil production efficiency ratio increases from 40% to 100%, and the oil production increases from 18,226 square meters to 40,745 square meters. Moreover, the profile test of NB17 well showed that water entry ratio in low permeability layer increases from 12.4% to 27.26%, resulting in water cut of corresponding production well declined from 54% to 32%. Our research validates that water-alternating-weak gel technology can improve water entry profile in the late stage of gel flooding and provide a new reference for the development of heavy oil resources in Bohai Oilfield of China.

Experimental Performance Evaluation and Optimization of a Weak Gel Deep-Profile Control System for Sandstone Reservoirs

“…Polymers with low concentration and slow-release cross-linkers could be mixed and injected into deep formation wells to develop the sweep efficiency, displace oil, and enhance deep-profile control. Since weak gels enhance molecular polymer migration and bulk gel profile control, these gels have become a focus of research. − Weak gel viscosity can range from 100 to 10,000 cP . Sheng stated that weak gels have significant flow resistance but can flow, enabling their injection deep into reservoirs .…”

“…Since weak gels enhance molecular polymer migration and bulk gel profile control, these gels have become a focus of research. 10 − 15 Weak gel viscosity can range from 100 to 10,000 cP. 14 Sheng stated that weak gels have significant flow resistance but can flow, enabling their injection deep into reservoirs.…”