Preparation of Hydrophobically Associating Polymer/Phenol/Formaldehyde/Sea Water in-Situ Gelling Fluid as Profiling/Water Shutoff Agent

The titled gelling fluid is prepared for use in Guantao formation reservoirs at Chengdao offshore oil field of Shengli,where the production wells become watered out as a result of water flood.For these reservoirs T=70℃,permeability in range 1.488—8.046 μm~2 and TDS in range 5.310—8.346 mg/L of formation water.To prepare the experimental fluid a simulation sea water of TDS=30.7 mg/L and a commercial polymer,NAPs,of M=1.092×10~7,hydrolysis degree 22%,cationic hydrophobe content 0.25%,swelling time 0.5 hour and dissolving time 2 hours are used.The optimal working recept of the fluid is(in g/L): NAPs 7—11+phenol 0.2—5.0+formalin 15—25+salts/heat stabilizer 0.10—0.15+reinforcer 1.0 and the gelation time is controllable.On tubular sand packs of higher permeability 6.895—8.821 μm~2,a water breakthrough pressure in range 26.21—36.74 MPa/m is observed after 8 and 10 g/L NAPs fluid having been injected and gelled at 70℃ over 72 hrs.Two sets of two tubular sand packs in parallel having been waterflooded to residual oil state are treated with 0.5 PV of 10 g/L NAPs fluid;all the fluid is entered into the higher permeable sand pack(of 8.062 μm~2 against 1.896 μm~2) for the set of inverse fluid injection(IFIS) and 98% of the fluid—into the higher permeable sand pack(of 6.70 μm~2 against 1.923 μm~2) for the set of equidirectional fluid injection(EFIS);a reversal of water uptake of higher and lower permeable sand packs is observed in the course of subsequent water flood for both sets and the ultimate enhancement in oil recovery from higher and lower permeable sand packs is of 3.3% and 28.1% for IFIS and of 5.6% and 23.7% for EFIS.Therefore the titled gelling fluid can be used for profile modification and water shutoff in the above mentioned reservoirs.