Optimization And Formation Protection Of In-flowing Fluid System In The Nanpu Oilfield

Formation damage control is a strategic problem in field exploration and development and it is also an important measure of improving well productivity.The clay mineral of the different layers about the reservoir of Dongying Formation in Nanpu Oilfield have high content and great difference. The reservoir has high water sensitivity. The formation water has high bicarbonate ion and carbonate ion, so calcium ion and magnesium ion introduction is easy to cause deposition and scaling. The reservoir is unconsolidated, there may be high stress sensitivity, so the invasion of foreign fluid are likely to cause great damage to reservoir.According to the reservoir features of Dongying Formation in Nanpu Oilfield, the potential formation damage factors and the physical and chemical properties of some kinds of operating fluids used in Nanpu Oilfield were tested and analyzed. On the basis mentioned above, the effects of formation protection of the some commonly used in-flowing fluids in the test area of Nanpu Oilfield were evaluated, including well control fluid, temporary plugging workover fluid as so on. According to the discussion, put forward corresponding improvements about formation protection, it is expected that the findings are of some help theoretically in stabilized production of Nanpu Oilfield and enhanced oil recovery.Obtained results in the study are as follows:(1)Based on the analysis of the reservoir features of Dongyi zone and evaluation of reservoir sensitivity, the potential formation damage factors mainly include:①The main reservoir of Dongyi zone is strong to extreme strong water sensitive formation, so the reservoir protection measures of oil production are especially important.②The main reservoir of Dongyi zone has certain flow rate sensitivity harm, in the higher than the critical velocity, part of the core appear particles migration damage, so reasonable injection-production rate should be controlled and prevent particles migration damage.③The formation water in Dongyi zone has high bicarbonate ion and carbonate ion, so calcium ion and magnesium ion introduction is easy to cause deposition and scaling, thus blocked formation damage.(2)According to the evaluation and selection of in-flowing fluid system used in Nanpu oilfield, the results show:①Killing fluid of fine quality(1.05g/cm3and1.2g/cm3),normal killing fluid(1.05g/cm3and1.2g/cm3),2%KCl and2%NH4C1basic do not have obvious surface activity and interface activity, Nanpu active water has certain surface activity and interface activity. At the same time, killing fluid of fine quality(1.05g/cm3and1.2g/cm3) and normal killing fluid(1.05g/cm3and1.2g/cm3) have certain solid particulate material damage. Killing fluid of fine quality(1.05g/cm3and1.2g/cm3) and normal killing fluid(1.05g/cm3and1.2g/cm3) which are improved have good basic performance, and have good thermal stability at130℃.②About the reservoir of ED1Ⅰ, normal killing fluid(1.05g/cm3),active water,2%NH4Cl,2%KCl are weaker in protecting reservoirs, the permeability recovery rate of cores respectively is50%,70%,65%,75%after polluted by the above fluids. Killing fluid of fine quality(1.05g/cm3and1.2g/cm3), normal killing fluid(1.2g/cm3) and2%NH4C1+10%water-locking removal agent can protect reservoirs effectively, the permeability recovery rate of cores is more than90%after polluted by the above fluids.③About the reservoir of ED1Ⅲ, the permeability recovery rate of cores is72%after polluted by normal killing fluid(1.05g/cm3), it is weaker in protecting reservoirs. The permeability recovery rate of cores is96%after polluted by normal killing fluid(1.2g/cm3), it can protect reservoirs effectively.④The microbubble workover fluid has excellent blocking effect and less damage to natural core in the layer of Nanpu oilfield. The microbubble workover fluid can protect reservoirs effectively, the permeability recovery rate of cores about the reservoir of ED1Ⅰ and ED1Ⅱ respectively are more than95%and70%after polluted microbubble workover fluid at80℃.⑤The formation damage is more serious by using solidify water, the permeability recovery rate of cores is less than30%,this is due to damage for some polymer particle into the core for high pressure. The permeability recovery rate of cores can be more than95%after further polluted by3%gel breaker JPC.⑥The permeability recovery rate of cores is57%after polluted by brine(1.03g/cm3), it is weaker in protecting reservoirs.⑦The permeability recovery rate of cores is75%after polluted by2%KCl, suggest using3%KCl, in order to fully suppress clay hydration dispersion of the reservoir.According to the research, several suggestions are put forward:(1)The main reservoir of Dongyi zone is extreme strong water sensitive formation, so salinity control of in-flowing fluid is important.(2) Killing fluid of fine quality(1.05g/cm3and1.2g/cm3), normal killing fluid(1.2g/cm3), microbubble workover fluid and2%NH4C1+10%water-locking removal agent can protect reservoirs effectively, the permeability recovery rate of cores is more than90%after polluted by the above fluids, it is proposed to promotion the use in the block.(3) The formation damage is more serious by using solidify water as single fluid. It is proposed to use gel breaker as combined fluid.(4) Normal killing fluid(1.05g/cm3),active water,2%NH4Cl,2%KCl are weaker in protecting reservoirs,there are some measures to solve the problem, include increasing activity, filtering, improving concentration as so on.(5)The water sample A, water sample B and brine have high solid content and high turbidity, so the killing fluid have high solid content, it is weaker in protecting reservoirs. It is proposed to use after filtering.