Experimental Investigation On Effective Radius Of Weak Gel Plugging System

Early development of low permeability oilfield, mostly taking various fracturing, exploitation. After long-term water flooding development, the reservoir will form the dominant flow channels. These composed of hydraulic fracture and natural fracture and big pore complex seepage flow system, increasing reservoir heterogeneity contradiction and matrix reservoir water flooding sweep efficiency is low, even water non-absorbent, and poor development effect; Daqing and Shengli oilfields often use polymer gel profile control and plugging to solve this problem, and has significant effects of increasing oil and decreasing water. So the weak gel profile control and water plugging technology is one of the effective ways to improve water flooding development.Changqing Oilfield is a typical fractured low permeability reservoir, layer between non serious heterogeneity, matrix reservoir permeability between 0.1×10-3 ?m2 and 5×10-3 ?m2, reservoir crack opening is generally between 40?m and 6000?m, high permeability zone in 100 ×10-3?m2 ~ 10000×10-3?m2, and low permeability matrix permeability ratio(permeability contrast) up to 103 ~ 104 orders of magnitude, or even higher. Changqing Oilfield BM central block profile control and water plugging in 46 wells which are used to HPAM polymer as the main agent of crosslinking system, there are 14 wells for profile control and water plugging effect is pretty good, which increasing the average amount of oil 300 t above that for low permeability fractured in Changqing Oilfield, and weak gel profile control and plugging technology is to improve the development effect of the important way; But others 32 wells poorly increase oil, that's because of some weak gel profile control and plugging effect is not ideal. The main reason is due to high permeability zone micro cracks and pore throat radius is different, the strength of plugging different lead to breakthroughs in gel to different pressure, surely of course driving ability and the role of crude oil in matrix formation are also different.This paper use Kozeny-Carman formula and ideal medium equivalent pore throat radius theory, and consider the mechanical porthole shearing effect. The effects of different shear strength into sizing effect and porthole shearing different permeability zone on the strength of plugging effect, low speed(less than 3000 r/min) shear plugging agent viscosity influence greatly, the ageing time affected is large, but the gel strength(the strength of plugging) had little effect on nucleation; The different hypertonic with permeability plugging test, that weak gel plugging 1.0m, theory can spread flooding for matrix formation leading edge radius relation chart, and the system for the block theory of optimum plugging radius relation chart; Hyperosmotic studies with impact on system migration plugging and polymer solution along the path of the apparent viscosity decreases, reduce characteristic curve is linear and end of apparent viscosity below 100 MPa, dropped by more than 90%; the multi-point pressure to investigate the effects of hypertonic with effective sealing distance and effective plugging rate, same slug conditions, maximum permeability 2000×10-3?m2 effective radius of plugging, in under the condition of the same permeability, effective plugging radius 1.0PV slug, but effective plugging rate is 0.6 PV. Maximum, achieve 80.53%. By improving the concentration of the crosslinking agent to obtain the new formula, compared with the old formula, the effective blocking rate increased by 12.3 percentage points.