The Further Improving Of The Water-flooding Oil Recoverery Using Weak Gel Control In Mongolian Oilfield

The weak gel control was usually used to improve water-flooding oil recovery in oilfield in recent years. Mongolian sandstone reservoir was initialed in October 1989. The cumulative oil production and composite water cut was 258.14×104t and 92.90% until the end of December 2002. Weak gel control was used to improve the oil recovery in Mongolian Oilfield from May 2005 to October 2008. The Oil recovery over water-flooding was 3.26% and the remaining recoverable reserves were 189.52×104t. A lot of remaining oil still exist in the block with the potential for improving water-flooding oil recovery. The vertical and plane remaining oil distribution features are studied by numerical simulation based on the theory of laboratory experiment. The optimization scheme of improving the water-flooding effect is used to enhance oil recovery based on geological characteristics and development practice.The results of laboratory experiment show that, the plugging capacity of weak gel on single reservoir decreases with the increase of reservoir permeability. The plugging capacity on reservoir will reach 98% when permeability is less than 20×10-3μm2. The plugging capacity of weak gel on high permeability reservoir increase and the plugging capacity on low permeability reservoir decrease with the increase of permeability ratio, and the shunt liquid volume of low permeability reservoir is strong compared to that of high permeability reservoir when permeability ratio is more than 4.3. There is a certain degree of plugging capacity on oil phase, but the plugging capacity of oil phase is strong compared to that of water phase, and the plugging capacity on water phase decrease when water drive is up to 30 PV. The plugging capacity of weak gel decrease with the aging of weak gel. The plugging capacity of weak gel decrease significantly when the aging time is longer than 80 d.The vertical and plane remaining oil distribution features show that, water injection profile is improved, which is consistent with the conclusion of laboratory experiment, but the improving effect is limited. There exists remaining oil of uneven distribution which makes Mongolian Oilfield have condition and potential to improve the water-flooding oil recovery. The remaining geological reserves of T1ys1-1 are 82.89×104t and the water cut of T1ys1-1 is 90.22%. So T1ys1-1 is unable to be the the main vertical productive reservoir. The remaining geological reserves of T1ys1-2-1 are 95.15×104t, which are slightly higher than that of T1ys1-1. The water cut of T1ys1-2-1 is 81.64%, so T1ys1-2-1 should be the main vertical productive reservoir for further exploiting. The remaining geological reserves of T1ys1-2-2 and T1ys2-1 are respectively 176.70×104t and 251.21×104t. The water cut of them are not high and they are respectively 91.18% and 91.97%, so they are the main vertical productive reservoir for further exploiting. T1ys2-2 and T1ys2-3 have the largest remaining geological reserves and they are respectively 251.21×104t and 278.81×104t. But the water cut of them are very high and they are respectively 94.82% and 95.46%, so they should be exploited on the condition of controlling the rising of water cut. Plane remaining oil mainly distribute in the small fault block, high position of local structure, the southern edge and uncontrolled area.The prediction results show that, cyclic water injection and perfect well network are better, so they are combined into comprehensive development scheme to study the effect on ultimate recovery and water-flooding effect. The cumulative water injection and the cumulative oil production will be 5599.45×104m3 and 489.22×104t, the ultimate recovery efficiency will be 33.65% until September 21, 2054 when the composite water cut is up to 98%. During the period from May 27, 2014 to September 21, 2054, the stage water injection and the stage oil production will be 2574.31×104m3 and 108.44×104t, the stage recovery percent and the stage water cut increasing rate will be 7.46% and 1.00%, the average composite decline rate and the average natural decline rate will be 6.40% and 6.40%. The average composite decline rate decrease 3.63 percentage points and the average natural decline rate decrease 8.14 percentage points comparing with that of 2013. Comparing to not use comprehensive development scheme, cumulative water injection increase 979.81×104m3, cumulative oil production increase 71.82×104t, ultimate recovery increase 4.94%.