| Introduction of the author:Tian Xiaolan, female, was born in Oct.,1985 whose tutor was professor Li Huabin. She graduated from Chengdu University of Technology in Oil & gas field development engineering major and was granted the Master Degree in June,2011.Porosity and permeability of Baolang reservoir are low,5.8%～13.2 and 4.6×10-3μm2～90.6×10-3μm2 respectively. The averaged water cut was increased to about 90%. Water flood technology is unfavorable used to recover oil, because of brine injection difficulties resulted from lower permeability and the so called five-damages, such as water damage, salinity damage, velocity damage, pressure damage, alkali damage and acid damage. So the acidizing and acidized fracturing could not be performed. The reservoir core flooding test results indicated that as follows.(1)The displacement pressure and its gradient increase with the decrease of permeability while the pressure and its gradient decrease with the increase of permeability. The displacement pressure and its gradient decrease slightly as the permeability is great than 4.904×10-3μm2,the gradients are the constants of about 0.32MPa/m,0.5MPa/m and 0.6MPa/m at the condition of without oil, oil displacing water and water displacing oil respectively.Furtherly, the displacement pressure and its gradient are from higher to lower order of the condition of without oil, oil displacing water and water displacing oil. The gradients are 5.5MPa/m～0.3MPa/m,8.41MPa/m～0.45MPa/m and 10.77MPa/m～0.6MPa/m in the permeability range from 0.176×10-3μm2 to 4.904×10-3μm2 at the situations mentioned above. The gradients of the three conditions vibrate swing un-obviously as the permeability is great than 4.904×10-3μm2.(2)The displacement pressure and its gradient are 10.77MPa/m and about 0.60MPa/m at 0.176×10-3μm2 and 22.65×10-3μm of permeability respectively. Therefore, the water flooding is difficultly used due to the higher gradient.(3)The water cut of single producer or the averaged water cut was in the range from 90%～95% if 0.2PV～0.3PV brine water was injected. The displacement pressure and its gradient increase very sharply in the injection. These still continue to increase for a long time though the water cut is in the range mentioned above.(4)The contact angle measured that brine is on reservoir rock. The wettability of rock is not hydrophilic when the contact angle is higher than 90°. The contact angle decreased with the increase of permeability.The injected pressure could be decreased through the lowering of interfacial tension between oil and brine and altering wettability in order to reduce the capillary pressure based on core flooding tests. The results of experiment which imitated actual oilfield situation were listed as follows(1)The chemical system of S-36/S-912 (the ratio is 1:1.5, total concentration is 0.05%) could be used to reduce injected pressure or improve the injectivity for Baolang oilfield. The capillary force could be reduced by 5.825×103 fold due to the interfacial tension between the chemical and crude oil being lowered to 1.244×10-3mN/m.(2)The contact angle decreased as the concentration of surfactant increased. The reduction is most obvious as the activity is from 0 to 0.1%.(3)The chemical system could be used to enhance the oil recovery for it could change the wettability of rock and reduce the capillary pressure.In this investigation, the chemical system used to reduce injection pressure was determined through the injection pressure and its gradient based on the core flooding testes. The study not only provides the theory of water flooding technology for baolang oilfield, but also supplies water flooding development guide for the low permeability reservoirs. |
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